en-us Thu, 02 Sep 2010 12:18:57 -0500 ATM@msgroup.org 60 *All Things Motorcycle* - Physics and the theoretical http://www.msgroup.org/forums/mtt/ *All Things Motorcycle* for Guest http://www.msgroup.org/forums/mtt/ http://www.msgroup.org/forums/mtt/rss_32.png *All Things Motorcycle* RSS Feed 144 47 Physics and the theoretical - A collision dynamics puzzlegreywolfhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=12195&REPLY_ID=116978Physics and the theoretical Fri, 27 Aug 2010 12:49:47 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=12195 I went by the area today. The boat looks untouched and a garage is up and being worked on. The only street marking on Nagle is the center line. There is no parking allowed during rush hour and the street normally has two rows of traffic in each direction then but no markers between the rows. At 6am, there still could have been some parked cars.]]>Physics and the theoretical - Rear brake lenghtens wheel base?jilphttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=12186&REPLY_ID=116914Physics and the theoretical Wed, 25 Aug 2010 12:33:16 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=12186 May be, I suggest, it is clearer to say that rear braking shortens the wheelbase less than front braking alone because...

The words tends to lenghten the wheelbase though is correct, could tend to be confusing in concepts.

Regards]]>Physics and the theoretical - Minimum speed at maximum leanIgorhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=12174&REPLY_ID=116648Physics and the theoretical Thu, 19 Aug 2010 15:13:45 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=12174 That lean angle calculator is very cool, thanks for creating it and posting it (and to the poster who linked it as well).

A couple questions:

CG % (rear weight bias)
I could determine this with a scale that could read up to 500lb. by weighing in each wheel and finding the ratio of rear/front but I lack one of those, so I'll assume for now that it's 60% as is the 'default' in the spreadsheet.

CG height
Any recommendations on how to approximate this value? Obviously I understand that there will be variance, depending on load and rider position, etc... The bike "feels" like its CG is lower than my seat, perhaps only by 2-3" maximum, however. (the seat height is about 27.6 inches)

I notice that CG height differential has negligible impact on lean angle, so this is not particularly important for my applications, but I remain curious how to get a better idea of the CG of my bike.

Width of front tire
I assume this is the overall width? I see my tire is a "130/90-16", I think meaning that the width is ~5.118 inches (130mm?)....

Oops, gotta run!]]>Physics and the theoretical - Air/fuel mixture and engine size/modificationsstaticattichttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=12003&REPLY_ID=116635Physics and the theoretical Thu, 19 Aug 2010 11:01:20 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=12003 On my Bug, sometimes I run an unbaffled stinger and other times I run a muffled dual quiet pack. When I would run the stinger, sometimes when I let off the gas, it sounded like I was shooting a shotgun. That always has frustrated me. I will ride with the stinger until the backfiring totally gets on my nerves, then I'll put the muffler back on. I am also a member of several VW forums. Here are some explanations they give about carbs, manifolds, exhaust, and backpressure:

Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.

The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

And another:

A common saying among auto enthusiasts is "you can't get it in if you can't get it out". This usually refers to the exhaust side of the equation, meaning all the heads, carbs and cam in the world don't mean a thing if you are still running a restrictive exhaust system. In this case, however, it's the opposite, assuming you've followed the trend of adding exhaust as one of your first upgrades. You now need to find a way to 'get it in' and a larger, less restrictive form of carburetion is the first step.

While there isn't really a large selection of carbs out there, there are quite a few configurations in which you can run them. First there is the center mount configuration. In this category you have the stock carb, the Bugspray carb, the Weber Progressive, and the center mount configuration of Weber IDFs and Dellorto DRLAs. Center mounts tend to be more popular among the off-road crowd for two reasons; float configuration is good for harsh cornering, and the central location protects them from debris. The downside is that the long intake runners needed to get fuel to the heads tends to cause fuel to drop out of the mixture and puddle in the runners. This problem becomes compounded by manifold icing when proper manifold heat is not present. These problems are most frequently recognized by low speed bucking and a stumble off idle. The most common fix is to just run the idle circuit richer, increase fuel delivery from the accelerator pump, and/or run emulsion tubes that bring the mains 'on' sooner. While these fixes work, they all harm fuel economy by causing you to run unnecessarily rich.

The next route is to take one of a few dual carb configurations. The low end of this setup is the dual 1bbl configuration, frequently seen as dual Weber ICTs, or dual Kadrons (actually Solex carbs). While both of these are a huge improvement over a single carb setup, they still have their restrictions. First and foremost, they are small. ICTs have 34mm throats, and Kadrons have 40mm throats. One advantage that Kads have over ICTs however is that there are larger aftermarket venturies available for them (contact www.lowbugget.com) to increase their flow capacity. The second down side is that being single barrel carbs, they are forced to feed two cylinders each. Even though only one cylinder pulls air at a time, you still have to consider that they are feeding two cylinders in progression of the firing order. Add a little reversion to the equation and one barrel will always suffer at lower rpms, commonly seen as an uneven idle when using larger than stock cams.

Finally, the most popular configuration is the dual 2bbls setup. In my opinion, this is what you should be thinking about when it comes time to upgrade. The three options you have here are Weber IDFs, Dellorto DRLAs, and the monstrous Weber IDAs. IDFs are available in 40mm, 44mm, and 48mm throat sizes. DRLAs come in 40mm, 45mm, and 48mm sizes. IDAs in stock form come only in 48mm throat size, though through the aftermarket they can be bored and modified to 51.5mm, or in spin off versions they can be found in 58 and 62mm throat sizes.

There are four things to consider when deciding the size and make: engine size; intended usage; budget; and if you frequent the drag strip, what fuel type, as IDAs are the only real choice for running alcohol. The rule of thumb that I would follow regarding engine size is 40mm for 1600s (1641, 1680), 44/45s for 1776 up to the two-liter range, and 48s for anything larger. As always there are exceptions, but this will provide good performance without the need to go out and buy costly venturi upgrades right away. Following this rule of thumb will also provide satisfactory performance in these displacement ranges for up to about 6500 to 7k rpms provided the rest of your engine combo is up to the task. If you wish to turn more rpms for a given displacement, then the next size larger carb should be considered. Likewise if you want to run a larger engine but plan on limiting your rpm range, smaller carbs will work.

Expect to spend about $800 for a set of either 40 or 44 IDFs, and $1000 for 48 IDFs. This price will get you manifolds and linkage as well. Dellortos are no longer available in new form so the price for these can vary greatly depending upon the condition of a used set. IDAs will run you over $1000 just for the carbs. For the sake of this article, my main focus will be the Weber IDF series as these are still available, and a much better choice for street use.

To get the best performance from your dual carb setup, it really helps to have at least a basic understanding of the working theory behind them. The easiest way to visualize it is to follow the path the fuel takes through the carb starting with the inlet valve and float bowl. The fuel enters the carb by passing through the inlet valve, also known as the needle and seat. The inlet valve is the first of the metering devices used to regulate fuel flow. It is a calibrated size and denoted by its size in thousandths of an inch. Hence an inlet valve with an opening size of .175" is known as a 175, a .200" is called a 200 and so on. There's no easy formula for calculating the necessary inlet valve size. It's not as simple as calculating the sums of the opening areas of the idle and main jets as these act under the influence not only varying, but a greater overall pressure than the inlet valve sees from fuel pressure. The best bet is to stick to what came with your carb setup and change it only if you find a fuel starvation condition exists at wide open throttle (WOT) during high speed.

Ideally you want to use the smallest size inlet valve you can safely get away with because as the size increases it also becomes more difficult for the float to control the fuel flow through the valve. In most naturally aspirated situations you'll find a fuel pressure between 1.5 psi and 3.5 psi to be best; experimentation is the key here. Which brings us to the float. The purpose of the float is to actuate the inlet valve as dictated by fuel level in the float bowl. A higher fuel level in the bowl will tend to make the mains come in sooner as well richening the entire fuel curve. A lower fuel level does the opposite. This is because the level of fuel in the bowl affects pressure on the backside (inlet side) of the main jet stack. It's the balance of positive pressure here and negative pressure in the carb throat that determines fuel flow through the carb.

The main jet is the next destination for the fuel. The fuel enters the bottom of the float bowl and passes through what's known as the jet stack. This consists of the main jet seated in the bottom of the emulsion tube, and the air jet seated on top. The main jet meters the fuel to match the requirements of the engine. The main jet mostly affects the fuel metering from about 3k rpms and up. Its size is also denoted by thousandths of an inch. Mains are available in increments of 5 and each change of 5 is commonly referred to as one size difference.

Next in line is the emulsion tube - a long cylindrical object that has a series of holes in it. The physical size of the tube is what determines the size of your fuel well. This fuel well is what prevents a lean condition under certain acceleration conditions. The larger the well, the more fuel that is delivered at specific points in the rpm range. The size and locations of the holes play a role in determining what rpm range the fuel well will affect enrichment. The word "emulsion" in emulsion tube refers to the fact that this is where air from the air correction is emulsified (mixed) with the fuel from the main jet. The numbering system for emulsion tubes is pretty nonsensical. With Webers the tubes come with F designations, such as F2, F7, and F11. The numbers really only mean when in the production series of the carburetors the tube was developed. So an F2 tube came before an F7 tube and so on. Don't forget these carbs were used in many different production cars over the years and not specifically designed for any one use. For reference though, the F2 tube is generally used when running alcohol, the F7 and F11 tubes are what most end up using in a VW application.

At the top of the emulsion tube you will find the air correction jet. The purpose of this jet is to add air to the mixture, generally from about 3500 rpm and up. Without the air correction jet, the main jet stops metering in a linear fashion in this range and an over-rich condition occurs. Air jets are also measured in thousandths of an inch. However, when speaking of air jets, one size is a change of 15. So if you were running a 175 air jet, going up one size would yield a 190.

Now that the fuel mixture has been metered, it's finally ready to enter the carb throat and be taken to the combustion chamber. The exit point for the mixture from the idle jet is through the progression holes near the throttle plate. These are a series of holes in a vertical fashion in the throat of the carb. The lowest hole should be just covered by the edge of the throttle plate. When you start to just crack the throttle this first hole becomes exposed which starts the fuel flowing. The holes above this first one continue flowing fuel together as the progression circuit. This circuit is active throughout the entire rpm range and overlaps the main circuit. This is also the circuit that is most responsible for the mixture under cruising conditions and thus plays a major role in fuel economy.

It should be noted that the idle mixture screws play no role with the progression/idle circuit per say. The mixture screws are only considered important at a pure idle with the throttle completely closed. The size of the idle jet will play a part in determining how far in or out the screws are adjusted, but they should never be used to correct an improper mixture condition at any point other than zero throttle.

The man circuit plays it's part from about 2500 rpm and up and becomes more and more pronounced as the throttle is opened up. So at WOT the main circuit plays a much larger role than the idle circuit. Fuel from the main circuit exits through the opening in the auxiliary venturi, the funny looking bulls eye part with a stack that is found on top of the main venturi. In Carbs that have been upgraded with a horizontal discharge tube (available from CB Performance) the main and Aux Vents are replaced by one large venturi/sleeve with a brass bar passing across the middle. The brass bar has a series of holes on its underside and this is where the fuel would exit the main circuit. The biggest advantage of a spray bar (horizontal discharge tube) is that it removes restrictions caused by the Aux vent.

Finally, the last part we need to be concerned with is the accelerator pump circuit. This is the part responsible for giving that shot of fuel when you step on the pedal. Without it your engine would bog every time your stomped your gas pedal. Air has mass just like everything else and thus inertia. As you open the throttle, it takes little time for it to start moving and this creates a short lean condition. This lean condition is remedied by the accelerator pump.

]]>Physics and the theoretical - Skid analysis eludes the liberal arts majorsasheppardhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11163&REPLY_ID=116216Physics and the theoretical Fri, 06 Aug 2010 12:58:31 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11163 James,

Sorry for adding more than I know and you implied. It is certainly not my expertise, but it all is very interesting to me.

Thanks again,

Alan]]>Physics and the theoretical - Center of mass effects in a turnmagicsmokehttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=12045&REPLY_ID=115577Physics and the theoretical Sun, 18 Jul 2010 19:03:32 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=12045 Thanks. The mist is clearing slowly.]]>Physics and the theoretical - Offset Leaning into TurnsIronHenryhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11799&REPLY_ID=115290Physics and the theoretical Fri, 09 Jul 2010 19:15:21 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11799 I'm not sure if I'm helping or just talking to hear myself talk, but here's what I've learned from a lot of miles on a sport bike. From my understanding, when you counter steer, you are moving the bottom of the bike sideways while leaving the top in place. Steering the tires out from under the bike to make it lean. It's very effective, and of course the best way to go about getting the bike to lean over at any reasonable speed. Leaning is required to counter the centrifugal force created during a turn. (Sorry if I'm covering complete basics, I'm just trying to put what's become second nature into words.) In any turn the front wheel is in fact turned into the turn. The bike follows a circular path because the front wheel is turned. Seems like a "duh" but some people I've talked to don't realize this.

I think the tires help pull the bike into a turn as well. More so as the lean angle increases. The edges of the tires are a smaller diameter then the center, so they travel less distance per revolution then the center portion. It seems to me that when you are all the way on the shoulder of a racing tire, that the contact patch is wide enough, and the difference in radius great enough, that the inside and outside portions of said patch are actually travelling at slightly different rates. I could be totally wrong, but at extreme angles the bike feels like it's pulling into or even sliding, ever so slightly, out of the turn, depending on what you are doing with the throttle. (Very small throttle adjustments of course.) Ok, ok, getting off topic.

At low speeds, I guess up to 25mph, I steer almost exclusively by pushing down on (putting weight on) one foot peg or the other. Sport bikes are tall and a bit top heavy. The front wheel doesn't turn very far. The pegs are also right under your body, so it's easy to more or less stand on them. Pressing on one peg or the other allows me to lean the bike without moving my body much. Basically I keep my body upright and level, but lean the bike. Or I lean my body to the outside of a tight corner, so I can lean the bike into the turn more. Because of the steering geometry, leaning the bike more "creates" (not sure on wording here) more wheel turn (deflection?) angle, allowing for a sharper turn. Try walking a light bike, or even with a toy motorcycle sometime. Turn the wheel all the way while the bike is straight up and then push it in a circle. Now do it again with some lean. Smaller circle huh?

25mph to about 60 mph I guess, I just counter steer. I might still push down on a peg or lean in a little, but if I do it's without thinking about it. Basic normal riding. Above 60, I start leaning my body into corners noticeably. Sometimes I do lean my body before I lean the bike. It does seem to make counter steering require less force. It also makes it so you don't have to shift your weight mid corner and possibly upset the bike. Depends on the corner I suppose.

I'm not quite sure what gyroscopic precession is (I did look it up, and still don't really get what it means) but at 90mph+ (on the track, where else?) it starts getting tough to turn that wheel in order to counter steer. At these speeds and in any back and forth corners, I shift all my weight to the inside peg, and pretty much throw my body into the corner while counter steering. It's the only way I've found to get the bike to react fast enough.


That's all I've got. If I'm just muddying the waters, being redundant, or just completely full of it, feel free to delete this. Just tossing out what works for me when I ride. I'm not saying it's best or even right, and I'm clearly no expert.]]>Physics and the theoretical - Buridan's Principlebachman1961http://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=12007&REPLY_ID=115264Physics and the theoretical Fri, 09 Jul 2010 01:43:31 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=12007
quote:
Originally posted by haithabu

I should mention one other way in which we can escape Buridans' principle. Unlike the ass, we have opposable thumbs and hence are able to flip a coin to make the decision for us.


The guys I ride with undoubtedly read that paper and took it to heart. The prospect of starving to death is nary a worry and although I don't always know where we'll pull off to eat, it's usually a 90 minute to 120 minute time lapse. I think they have something programmed into their steering damper. [:D]

~brian]]>Physics and the theoretical - Safety Tip 045 - "Dragging a Peg" 101staticattichttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11835&REPLY_ID=113917Physics and the theoretical Fri, 28 May 2010 19:47:47 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11835 D'oh!!! I don't know how I missed the "Search" button. I have been reading posts off and on all day today about this exact topic. Quite interesting. Sorry for the re-ask of a topic that has already been so deeply discussed...]]>Physics and the theoretical - Crash Scenario Questionscottrnelsonhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11642&REPLY_ID=113910Physics and the theoretical Fri, 28 May 2010 15:24:42 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11642
quote:
Originally posted by waxclan

2. Once the bike goes down, keep a hold of the handlebars and stay with the bike if possible. In traffic, drivers will see the bike as the target to miss and may not see the rider.
Back in 1986 or 1987 I crashed a bike by giving it too much front brake and was down on the right side before I knew it. I was only going about 20 mph when the bike went down. That was probably the last time I ever rode on the street without gloves, because my right hand was "protecting" the handlebar as we slid along the road. I had to consciously think to let go of the bar.

There are times when letting go of the bike is the right thing to do.

The other two times I've crashed (1984 and 2003), I didn't have a choice to hang onto the bike or not.]]>Physics and the theoretical - Coasting through turnsricbassmanhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11779&REPLY_ID=113513Physics and the theoretical Sat, 15 May 2010 21:17:59 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11779 That makes a lot of sense. It's not my normal routine to coast through a curve like that, so of course it feels different, and different can translate into unstable.]]>Physics and the theoretical - Weight relative to distance above center of wheelgreywolfhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11772&REPLY_ID=113473Physics and the theoretical Fri, 14 May 2010 01:36:38 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11772 That tip rings all kinds of bells with me. I've had a couple of light front end experiences at high speeds from the wilder moments of my past, including flying a Vetter Windjammer fairing that caused a complete loss of steering input on a Yamaha XS110E at 106mph in 1978. I'd add that fairings and windshields can add lift depending on their shape. Having the air stream above move faster than the one below creates lift like a wing would due to Bernoulli's principle.]]>Physics and the theoretical - Options entering a turn too hotrbperriehttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11704&REPLY_ID=113341Physics and the theoretical Mon, 10 May 2010 19:30:19 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11704
quote:
Originally posted by James R. Davis

When you hit your brakes in a turn (at counter-steering speed), you compress your front shocks which causes two things to immediately happen: the bike lowers and it tries to stand up - decreasing its lean angle.

It is the lowering that should get your attention in this scenario as you are already 'dragging a peg'. It is for that reason that hitting the brakes when you drag a peg is absolutely the worst thing you can do.

If you are already braking hard when your pegs begin to scrape, you are also tightening the turn - not a good thing. But as has been pointed out already, your speed will decrease rapidly and that, in turn, causes your lean angle to reduce - lifting your peg off the ground.

The idea that "you can lower your CG by leaning/sliding your body to the right side of the bike" is exactly the right thing to do! You do not have to adopt a racer posture or 'hang off' your bike to correct the immediate problem - just lean your upper body INTO the turn and that will, by itself, lift the peg off the ground.


James, thanks for your response and it prompted me to do some experimenting of my own. So I did some "seat of pants" testing since posting this topic. I had always assumed that to get any significant increase in lean angle by shifting your weight to the inside of the turn one would have to assume the racer position to get any real benefit.
Well last time out for a day's riding when I would take a turn at a significant lean I would shift my weight to the inside of the turn. What surprised me was how little of a shift was required to get a noticeable improvement in lean angle. Riding a heavy cruiser I'm not interested in hanging off the side yet I found that simply leaning into the turn by just lowering my head down towards the handlebar made a noticeable change and I didn't even have to slide my butt over at all.
So my summer project this year is working on the shifting of the body weight to maximize the improvement of the lean angle should I ever get myself into that ugly scenario I started the thread with. Thanks for all the discussion.]]>Physics and the theoretical - Lean angle data recorderscottrnelsonhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10382&REPLY_ID=113281Physics and the theoretical Sat, 08 May 2010 09:24:04 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10382
quote:
Originally posted by DeaminRacing

Here's a link to the video if anyone is interested:
http://www.youtube.com/watch?v=GX56jMII2FU
Thanks for sharing the video. It looks a little wobbly, but when I occasionally get out my Jeremy McGrath Stunt Cycle, it's wobbly too. And I'm not usually as accurate steering it as you seem to be.

I think you've brought a new meaning to the term Parking Lot Practice. [8D]]]>Physics and the theoretical - Interesting videos about race tiresscottrnelsonhttp://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11683Physics and the theoretical Wed, 21 Apr 2010 13:24:49 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11683
http://www.asphaltandrubber.com/rac.../#more-10181]]>Physics and the theoretical - Enhanced modelsAndrew Dresselhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11591&REPLY_ID=112296Physics and the theoretical Mon, 05 Apr 2010 13:58:23 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11591
quote:
Originally posted by James R. Davis

This has been an absolutely delightful thread ...


Yes it has. Thanks for putting up with my insistence on getting to the bottom of things.]]>Physics and the theoretical - Busted for drag racing at 111 mph over the speed limitJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11461&REPLY_ID=111120Physics and the theoretical Thu, 18 Feb 2010 17:37:38 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11461 According to the sergeant (Mark Kimsey), "The incident happened several years ago in Chattanooga, Tennessee and was part of an aggressive anti-drag racing program (HEAT), in which they develop information sources and use other means, to learn where and when future organ donors are going to be drag racing motorcycles and cars."

He wrote it up as part of a Crash Reconstruction Association document that was sent to me a couple of days ago.]]>Physics and the theoretical - Brake lever force vs speedDataDanhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10818&REPLY_ID=111043Physics and the theoretical Mon, 15 Feb 2010 16:57:16 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10818
quote:
gymnast wrote: "I ease the brakes as I am about to completely halt" is a technique that was taught at the Rolls Royce Chauffeurs and Owners School (I don't believe the school exists any longer) to provide as smooth a stop as possible and involved easing the brakes during the last few feet of travel so as to provide the smoothest and least upsetting stop for the passengers.

I got the lesson gymnast described when I first learned to drive, erm, many years ago. My instructor, our next door neighbor (my dad taught the neighbor's kids), explained that the phenomenon of increasing deceleration with constant pedal force as speed nears zero is because static friction is greater than dynamic friction. As relative speed between the drums and shoes (yes, it was that long ago) approaches zero, the coefficient of friction increases and thus deceleration rate increases if pedal pressure remains constant. He was geeky enough to think in those terms (an engineer on the XB-70 Valkyrie), and I was geeky enough to (barely) understand it.

I have no data confirm this hypothesis, but it seems reasonable to me. FWIW, I take pride in my ability both on a motorcycle and in a car to use the technique of easing off pressure "to provide the smoothest and least upsetting stop for the passengers," as gymnast put it.]]>Physics and the theoretical - Counter-steering in pictures (continued from General Discussion)Ken Chttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11428&REPLY_ID=110954Physics and the theoretical Fri, 12 Feb 2010 12:54:54 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11428 Ahhhh, countersteering. One of my favorite discussions.

http://www.ridinginthezone.com/page...eo_Home.html The video at the top of the page shows countersteering pretty well. The "ants" eye view segment has a good view of outtracking.]]>Physics and the theoretical - Bicycle and Motorcycle Dynamics 2010 SymposiumAndrew Dresselhttp://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11444Physics and the theoretical Thu, 11 Feb 2010 09:36:16 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11444
Bicycle and Motorcycle Dynamics 2010
Symposium on Dynamics and Control of Single Track Vehicles,
Delft University of Technology, Oct 20-22, 2010

Scientific Committee
  • Vittore Cossalter, University of Padua, Italy

  • Ichiro Kageyama, Nihon University, Japan

  • Jaap Meijaard, University of Twente, The Netherlands

  • Hans Pacejka, Delft University of Technology, The Netherlands

  • Andy Ruina, Cornell University, USA

  • Arend Schwab, Delft University of Technology, The Netherlands (Chair)

  • Robin Sharp, University of Surrey, UK

  • Werner Schiehlen, University of Stuttgart, Germany

]]>Physics and the theoretical - Theoretical Physics questionalblancherhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11305&REPLY_ID=109862Physics and the theoretical Sat, 16 Jan 2010 11:33:35 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11305 They use very low frequencies for communication. I believe they normally use elf to alert the submarine of an incoming message. The sub will approach the surface to a depth that the radio/data antenna functions and higher speed communications are available.

I do not know and do not wish to know if the military GPS has a low frequency channel just for this purpose.

Don't need any knocks on the door at 11:00 at night.]]>Physics and the theoretical - Total Time to Full Load Brakinggalileohttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10881&REPLY_ID=109810Physics and the theoretical Fri, 15 Jan 2010 13:50:39 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10881
quote:
Originally posted by Moses

In "Proficient Motorcycling", David Hough suggests counting out an even, steady "one thousand and one" while applying the brake, squeezing progressively harder as you count, trying to reach maximum pressure at the end of the count. I like this technique, and I use it all the time while practicing quick-stops.

The thing I like best about it is that it trains you to apply the brakes progressively, and trains your body to do it that way instinctively, even in an emergency.

IMO, if you don't practice braking (progressively applying pressure), then you may panic in an emergency and "crush" the brake levers and lose traction. Of all the practice exercises that I do, I consider quick-stops to be one of the most important.

ALSO - don't forget that covering the front brake drastically reduces the initial reaction time when applying the front brake!


Although I agree with your conclusion, I found some other things testing braking with a bike with ABS and applying both brakes rapidly instead of progressively.

In a video of the g-meter, I saw that the full g force wasn't attaind for 1 to 1.25 seconds. During this time, the front tire ABS often cycled. Then after, the rear tire would cycle.

My conclusion is that I can immediately apply the amount of rear brake I know won't induce a skid later. And then progressively apply the front brake as the weight transfers while the g's are increasing.

This weight transfer is not instantaneous, but it may be significantly different, probably based on the height of the CG.

The only way to find out is practice while paying attention to what is happening.

(Note: I'm NOT recommending intentionally inducing a skid, nor am I recommending practicing above 20 mph.)]]>Physics and the theoretical - Question about centrifugal forceJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11082&REPLY_ID=108191Physics and the theoretical Sun, 29 Nov 2009 12:06:43 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11082 Just so we are clear on our terminology again ...

I agreed that driving and braking forces cause a YAWING torque moment, not a ROLL torque moment.]]>Physics and the theoretical - Excel CG CalculatorJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10143&REPLY_ID=106806Physics and the theoretical Sat, 17 Oct 2009 14:56:16 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10143 http://www.msgroup.org/forums/mtt/t...OPIC_ID=4675]]>Physics and the theoretical - Learning braking techniquesbachman1961http://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10884&REPLY_ID=106378Physics and the theoretical Sun, 04 Oct 2009 10:55:02 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10884
Panic stop, quick stop , short stop or emergency stop ... yeah, I hear you.

It's tough to know how someone else defines the term and their individual application. IMO, the tips you mention and / or reference from other sources do work and help to the extent they are practiced. If these 'others' are out doing some practice braking at lower speeds to find the feel and near threshold of a skid, that would ideally accomplish the mission of reacting consistently with the use of braking pressure to effect a safe quick stop. I also tend to think this type of PLP drills into my mind the likelihood and potential for evasive action .. making the event more of a planned situation likely to be used, less of a 'panic'.
Panic is a term that can easily be identified with someone 'freezing' and not doing anything due to fear.
I think the essence of PLP coupled with this braking stuff is paying rewards to many who (by their own words) are surprising themselves in the event or incident by their ability to not panic and safely stop with room to spare. They are posting these experiences here on this site, thanking James and others for the tips and these types of threads. No matter what they call it, I hope the PLP keeps paying off for the quick stops.
Maybe the worries of an emergency stop at 75 mph can be mitigated by better threat perception, appropriate speeds for the line of sight and the same PLP braking exercises at low speeds. Some mention the practice of quick slows like from 60 mph down to 30 mph. That makes sense to me when done in a safe setting.
Do people get so preoccupied with PLP braking they reduce the importance of controlling speeds to the conditions and good scanning habits/threat perception? Maybe in some cases braking is a crutch for a shortage of other skills.
What about line of sight versus width of the country two lane with trees as the shoulder...?
I've been down plenty of roads where I can see a mile ahead or more, but the varmint might be 12 feet to my left or right in the weeds.
If I get too much practice with quick stops on the roads, it could be could a symptom rather than a cure.


~brian

]]>Physics and the theoretical - Backpressure46raymohttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=4134&REPLY_ID=106278Physics and the theoretical Thu, 01 Oct 2009 20:46:36 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=4134 Ok I've read all of this post, but dodn't find my answer to my problem. 1984 Honda Magna 700. I installed exhaust from Harley Sportster (less back pressure). Gas mileage went from 50-52, down to 40-42. Pipes are black inside. Everything on this forum says I need larger jets but mys symptoms seem to indicate smaller jets. Bike runs fine with no flat spots.]]>Physics and the theoretical - Counter steering.Andrew Dresselhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10905&REPLY_ID=106133Physics and the theoretical Mon, 28 Sep 2009 15:12:41 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10905
quote:
Originally posted by galileo
Andy, it seems that in the article I posted the author is in favor of riding on the "critical speed" line where forces on the handgrips are neutral. Please correct me if I've defined the critical speed line in your article incorrectly.

The 2007 paper by Cossalter, Lot, and Peretto called "Steady turning of motorcycles" and submitted to Proc. IMechE Part D: J. Automobile Engineering defines transition speed as the speed at which the vehicle transitions from negative to positive steering torque. It continues
quote:

The transition from negative to positive steering torque is important because it corresponds to the transition from stable to unstable capsize conditions.


It also defines critical speed as the speed at which the vehicle is cornering even if the steer angle is null, a function of tire slip angles. It is the boundary between over-steering, when the side-slip of the rear tyre is greater than that of the front tyre, i.e. the actual cornering radius is smaller than the ideal value; and counter-steering, when the side-slip of the rear tyre is much greater than that of the front tyre and, to compensate for this condition, the handlebar must be steered away from the curve (i.e. negative steering angle).

Finally, it concludes:
quote:

... negative steering torque and positive steering ratio [oversteering] ... are correlated to good handling; the capsize mode is in fact stable, the steering torque decreases approaching zero as lateral acceleration increases (thus requiring lighter rider effort as roll angle increases), and favourable over steering behaviour is achieved. It follows that these combinations of speed and lateral acceleration can be considered a preferable driving zone.


quote:
Originally posted by galileo
This can be affected by the amount the rider leans off. At advisory speed, this isn't a dramatic lean. Personally, I'm NOT in favor of this for newer riders as it can disguise the countersteering. It's much simpler to sit erect until it's completely internalized.


For the physical experimentation, they specifically avoided rider motion relative to the bike so that vehicle response ratios and gains can indeed be measured in a repeatable and useful way.

]]>Physics and the theoretical - Motorcycle Braking Dynamicswhittlebeasthttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10763&REPLY_ID=105849Physics and the theoretical Sat, 19 Sep 2009 08:57:05 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10763 A fully warmed up new autocross tire on an a-mod car is in the range of 1.6 CofF

Street derived autocross rubber is in the 1.2 range

Street car rubber is in the 1.0 range

I can fairly routinely hit .85 geez braking in my 2008 FZ1 using only the front brake on normal aged concrete.

This is the traction circle coming of my autocross/street driven STI wile beings raced in a driving rain storm.

see http://www.youtube.com/watch?v=qzb7ERHdIKU for the matching video

Hope this helps

WB]]>Physics and the theoretical - Question about weight transfer, anti-dive and brakingwhittlebeasthttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10834&REPLY_ID=105846Physics and the theoretical Sat, 19 Sep 2009 08:24:37 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10834 This spreadsheet will calc almost everything you would ever need to know about motorcycle braking. It happens to be set up for my wifes single Brembo equipped Harley Sportster.

http://www.ncs-stl.com/motorcycle/brakeCalcs10.xls

Hope this helps

WB

]]>Physics and the theoretical - A question about tank slappersscottrnelsonhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10833&REPLY_ID=105670Physics and the theoretical Mon, 14 Sep 2009 17:41:48 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10833 I experienced a tank slapper in 2003 and have written a few things about it on this site. In my case, it came on so quickly that there wasn't much I could do about it. I certainly couldn't do anything with any of the controls on the handlebars.

There are a few specific motorcycles known for a higher tendency to have tank slappers. The early Ducati Monsters were one such bike, with a 23 degree rake. I think the Suzuki TL1000 also was known for that. A good steering damper helps considerably for those bikes.

I wouldn't bother trying to put a steering damper on a V-Star, though.]]>Physics and the theoretical - The physics of trail bike ridingGarry_Coateshttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=6008&REPLY_ID=105498Physics and the theoretical Tue, 08 Sep 2009 20:51:00 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=6008 Hi All,
it has been two years since I raised this question and I have now been finally able to resolve it.

To get the XR600 to handle with me in deep sand, I have:
1. Changed spring rates
2. Changed suspension settings
3. Raised the handlebars approx 1.5 inches
4. Put on a bigger front tyre (90x100mm)
5. Regular practice

The change that made the biggest difference is going from a 80x100 to a 90x100 front tyre. This tyre is wider with a slightly greater diameter. It is now possible to ride away seated the nstndup and surf the front. Tested it again in the Little Desert in late August.

regards
Garry

]]>Physics and the theoretical - An interesting paper on motorcycle steeringAndrew Dresselhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10812&REPLY_ID=105387Physics and the theoretical Sat, 05 Sep 2009 19:59:26 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10812
quote:
Originally posted by galileo

The information is also on page 111 of Motorcycle Dynamics.


Yes, certainly much of the ground work for the paper is also covered in the book. What is new is the graph of "zones" and the physical experiementation with different types of bikes showing how they move from zone to zone or not as conditions vary.]]>Physics and the theoretical - Motorcycle Aero Dynamicsgalileohttp://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10770Physics and the theoretical Tue, 25 Aug 2009 13:54:24 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10770
Later, I'll devise an experiment to determine the coefficient of Drag. It will take a day with a strong wind out of one of the cardinal directions.

James,

I had a few questions about the DragLift calculator.

In B30 and 31, it shows a positive number for both wheels. I can see how the front tire has less weight, but shouldn't the rear tire then have more?

Does the program assume a constant speed? If so, shouldn't the numbers be increased by the rotation caused by the additional force required on the rear wheel to keep the bike at the same speed?

Are you considering lift as in a wing or are you using the term to describe Ntr (Load transfer)

I'm not going to play with the gravitational constant. Too much work for now, but I agree with the calculation.

Just general answers will be fine. I'm going to try to reproduce the math just for fun.

]]>Physics and the theoretical - Seeking CoF dataMike W.http://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10768&REPLY_ID=104927Physics and the theoretical Mon, 24 Aug 2009 23:33:43 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10768
quote:
Originally posted by galileo

Mike,

Try googling Traffic Engineering Handbook Static Coefficient of Friction. States make different parts of it available. A 1951 edition is available online here. It will give an idea of what would be in the new one. It's not that expensive to buy. I think about $40.

Hope this helps.


Hi Galileo,

thanks for the pointer... looks like a great text and I saved that to my disk for later use. Unfortunately, if you look close, everything in there as well is talking about dynamic/sliding CoF. I just cannot believe how much the dynamic CoF dominates the available data... it's only used in the aberrant case of a loss of traction. You'd think the conventional case would be all over the web, but so far, nothing.

Either way, great book and thank you.

Mike

]]>Physics and the theoretical - LOWERING HD SOFTAIL DELUXESkootchNChttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10689&REPLY_ID=104923Physics and the theoretical Mon, 24 Aug 2009 18:50:55 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10689 Harley makes a "REACH" seat, it lowers the rider, as well as moves the rider forward. It also has a narrower front.
All of this and it's cheaper than chasing the suspension

Good luck
Frank]]>Physics and the theoretical - Video of effects of leaning on turningBearyhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10680&REPLY_ID=104571Physics and the theoretical Fri, 14 Aug 2009 13:14:38 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10680 I was coming home from moving my daughter into her dorm at Oklahoma State and I had a very quiet pleasant ride home on a on a quiet road. So thinking about the roll question, I purposely dodged spots in the road that were right in front of the bike. Logic would suggest that I need to steer the bike left to go left of the spot. But the initial counter steer right moves the wheels right (out tracks). Now we can either assume the whole bike goes right, which we know it doesn't, or the bike is rotating somewhere farther up the vertical plane. I suspect very near the CG.

So the bike is not rolling around the ground/tire contact point like hinge because it can slide sliding over laterally.

I agree there are a lot of forces and reactions interacting, but have you ever really thought about where the wheels are in a quick reaction to dodge that suicidal squirrel? If he is close enough, you might go the wrong way. [88]

Hey thanks for a fun discussion.

Beary]]>Physics and the theoretical - Does the motorcycle lean or roll around the CG?Bearyhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10720&REPLY_ID=104493Physics and the theoretical Wed, 12 Aug 2009 16:31:38 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10720
quote:
Originally posted by The Meromorph

One of the things I was trying to convey is that the motorcycle is not exactly attached to the ground.
Yes it always(?) has a 'point' of contact with the ground that is 'rigidly attached' by friction, but each actual point of contact is neither a point, nor fixed, and is within a contact 'patch' that is itself actively changing, and moving, and the point itself may be 'squirming' within the contact patch.

As I admitted before, my brain hurts.... [:x)]




I was thinking along those lines as well and even though a free body rotates around the CG, we might expect the friction to slow down the roll rate to some small degree that would knock it off axis.

Beary]]>Physics and the theoretical - Large bump and your front tire is now in the air - what happens when you come down?scottrnelsonhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10713&REPLY_ID=104392Physics and the theoretical Mon, 10 Aug 2009 15:24:20 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10713
quote:
Originally posted by Beary

But I watch the motocross guys making these decisions dozens of times on each lap of the course. I imagine it would just require a little practice somehow or another.
You cannot apply all of the dirt riding skills directly to riding in pavement. Specifically, a dirt bike will not suddenly yank the bars out of your hands if you land with the front wheel a bit crooked. Some of the rear tire sliding skills from dirt riding are more applicable to street riding, but you still don't have the same dangers. For example, it's pretty hard to get a dirt bike to high side when the rear is sliding around on the dirt.

I have no concern at all about catching a little bit of air with the front tire on a dirt bike and coming back down with the front wheel turned a bit. I would be seriously concerned about doing the same on a street bike.]]>Physics and the theoretical - Tire Traction. Is contact patch size important?Night Trainhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10628&REPLY_ID=103719Physics and the theoretical Tue, 28 Jul 2009 14:43:07 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10628
quote:
Originally posted by dhalen32

Moses and Night Train:
With all due respect I hope that both of you take it easy when going around corners for the first five to ten minutes of any ride. Regardless of initial starting pressure, tires, like you and I, work a little better when they have had a chance to warm up to their optimum temperature. That applies to a parking lot, a street or a racetrack. The tires cannot tell the difference where they are rolling.

No one has advocated racing techniques on the street here. For the record, I think you will find that tires have maximum pressures at maximum load molded into their sidewalls. Actual operating pressures should be adjusted according to load (# of passengers plus cargo) and intended use. These pressures can be found in your owner's manual and the tire manufacturers' websites.

Lighten up ... this is a physics and theoretical thread.
Dave

Point taken in respect to the thread and the topic. I'm pretty cognizant of tire pressure in relation to the loads I carry and the type of roads I travel but I honestly don't have any appreciation for what someone may do with their tires on a race track.]]>Physics and the theoretical - Front Brake Stands Up BikeJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=8752&REPLY_ID=103069Physics and the theoretical Tue, 14 Jul 2009 16:19:48 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=8752 LOL

Yes, I have written a novel (thriller that was not published nor even entered final edit) and a couple of children's short stories (published four decades ago), but I take it you mean relative to motorcycle safety and/or dynamics. That I have not done though I have prepared perhaps 5 million words toward that end. [8D]]]>Physics and the theoretical - Neutral Steering (fact or fancy?)James R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10482&REPLY_ID=102729Physics and the theoretical Mon, 06 Jul 2009 17:54:20 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10482 I've had it for a few months but it is so terribly dense that it has taken me a very long time to finish it. Indeed, my calculus skills are very weak but my linear algebra skills are almost nonexistant. It was not unusual for me to have spent over a week trying to understand a single page of this fascinating book.]]>Physics and the theoretical - handling tradeoffs with varying wheel sizesAndrew Dresselhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10379&REPLY_ID=101581Physics and the theoretical Thu, 11 Jun 2009 22:54:09 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10379
quote:
Originally posted by James R. Davis

I quoted something by Andrew that is a misrepresentation of reality - and it happens to be a commonly held myth or misunderstanding. That myth is that the size of the contact patch determines how much traction exists.


First, sorry about going missing. I've been travelling today, all day. USAir, oof.

Second, I was paraphrasing the article, which was quoting Jim Papadopoulos, co-author of the 3rd edition of Bicycle Science.

Third, I certainly know the Coulomb friction model, which is independent of surface area, but it is only a model, and I believe it depends on solid surfaces. I suspect it poorly predicts the traction available on loose surfaces. What difference does the coefficient of friction between rubber and sand make when the sand just gives away?

I didn't bring the article with me, and I can't find it online, so I can't look for why the author thought a larger wheel would give better traction until I get back, sorry.

Okay, here, finally, is the full quotation:
quote:
from page 60 of the July issue of Mountain Bike Magazine

It's commonly said that 29-inch wheels have a larger contact patch than [26-inch]. In truth, it's only differently shaped. Papadopoulos estimates that a 29er's contact patch is narrower, but about 5 percent longer, which can have a positive effect on traction, but adds that the difference is so small it's unlikely to be noticeable.

The article does not elaborate on why this might be. I'll email him and see if I can get an answer.


Perhaps it is something along the lines presented in this paper.
http://www.orsis.de/Papers/1996_Bre...%20_Lach.pdf

I'll keep looking.

Ooh! Here's a good one: http://rrosca.tripod.com/agro03.pdf
WHEEL TRACTION PREDICTION ON AGRICULTURAL SOIL
The tractive force is given by the relation: Ft = s At [kPa], where s is the "shear stress" in the soil and At is the area of the contact patch.
]]>Physics and the theoretical - A positive reasonbachman1961http://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10336&REPLY_ID=101281Physics and the theoretical Sat, 06 Jun 2009 22:54:28 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10336 This is not relativistic, but I have heard that happy people live longer than stressed out people. My bike makes me very happy when I ride. It also relieves stress. By that theory, if I keep riding, I may live forever. No time shifting necessary, nor any need to understand physics at the relativity level[:D]]]>Physics and the theoretical - Weight TransferGeotiggyhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=2224&REPLY_ID=101233Physics and the theoretical Fri, 05 Jun 2009 21:04:35 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=2224
quote:
Originally posted by James R. Davis

What pushes the vehicle forward is not important in any way relative to weight transfer. What is important is where that propulsion thrust is coming from relative to the CG - that is, how high it is as compared to the height of the CG.

So, for example, if your front wheel drove your bike instead of your rear wheel, the weight transfer experienced by acceleration would be exactly the same as that thrust is coming at ground level in either case.

If you mounted a propeller or a jet pack instead of using your wheels to provide thrust, and if that thrust was being provided at the same height as the CG, there would be NO sense of weight transfer. If the thrust was coming from a prop or jet pack that was higher than the CG, acceleration would cause weight to transfer to the front instead of to the back.



Indeed that makes the physics involved much easier to envision. Thank you!!
]]>Physics and the theoretical - Why does lean cause turngymnasthttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10261&REPLY_ID=100925Physics and the theoretical Sun, 31 May 2009 10:55:50 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10261 Andrew, your calculations look good to me, and have got me to wondering if those people featured in the "dysfunctional family chopper building shows" use similar math in designing the front ends of their circus bikes.[:D]]]>Physics and the theoretical - Looking for a technical paperCash Anthonyhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10232&REPLY_ID=100558Physics and the theoretical Sat, 23 May 2009 11:09:35 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10232 DataDan wrote
quote:
The real payoff is in the combination of actions: By slowing down, covering the brake, and shifting lane position, a rider can reduce exposure time by at least half and in some cases eliminate it, even when braking at only .5g, For braking at .75g, those same actions eliminated the vulnerable zone completely in every test case.
This is a hugely important finding, I think.

Both individuals who ride solo and all group riders especially should pay attention.

I mention group riders, because it's easy for position-keepers to forget that they own the entire width of their lane, and can move away from danger without fear of being hit by the bike to their rear.

The margin of safety between the bikes is reduced - cut in half - when a rider takes a position in a different slot and directly in front of the trailing rider. At highway speed, the time when the rider is out of position is usually very short, i.e., to swerve around debris in the road, and the extra risk exists for only a few seconds. Yet when this defensive lateral move might most be needed -- that is, when traveling on the surface streets with many intersections and driveways -- is when most group riders get bunched up to move as a block at slow speed, going through a town.

Very, very interesting. Thanks for pointing that out, Dan.


Cash]]>Physics and the theoretical - Rake Angle Determines Steering EfficiencyJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10229Physics and the theoretical Sun, 17 May 2009 00:25:15 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10229
I have maintained that the rake angle of your bike's front-end determines how efficient your steering is. That is just another way of saying that the smaller the rake angle is, the 'quicker' its steering will be.

Below is a chart I constructed to try to demonstrate this concept for you. Along the horizontal axis I chart your steering input in degrees and along the vertical axis I chart your turning angle, again in degrees. The legend shows various rake angles from 0 to 45 degrees.

You will note that if you had no rake at all then no matter what steering angle you input, the resulting turning angle will be identical. But as you increase your rake angle you find that it takes a larger and larger steering input to accomplish the same turning angle. Thus, the greater the rake angle, the less efficient your steering is. A chopper steers like a pig, and now you know why.

For example, if your rake angle is 45 degrees (like some choppers) and you turn your handlebars 36 degrees, you would change your direction of travel slightly more than 25 degrees while if your rake angle is 33 degrees (about normal), then if you turn your handlebars 36 degrees, you would change your direction of travel approximately 30 degrees.



The reason for this change in steering efficiency with different rake angles is pretty obvious. The greater the rake angle, the more of your steering input is translated into a tilt of the front wheel as opposed to an angular change in where the contact patch points.]]>Physics and the theoretical - Stability of Scooters vs Cruisersgymnasthttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9970&REPLY_ID=99505Physics and the theoretical Sun, 03 May 2009 21:21:05 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9970 Camber angle and toe in become particularly relevant when setting up a side car. The Vetter Terraplane side car featured a means by which you could adjust the camber angle while underway so as to trim out the car for more neutral steering.]]>Physics and the theoretical - Oil cooling an air cooled engine?KLShttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9351&REPLY_ID=99434Physics and the theoretical Sat, 02 May 2009 14:47:43 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9351 The oil is always cooled by some means. If no oil cooler is fitted, the oil is cooled by air passing over the sump and by conduction through the engine metal to the water jacket or air cooling fins.]]>Physics and the theoretical - Dynamics of low speed turn/brake crashJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=8262&REPLY_ID=98154Physics and the theoretical Mon, 06 Apr 2009 22:17:05 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=8262 I acknowledge that you have joined us to learn some things and that you had no idea that you were 'providing advice'. So, given that, how about we get real here?

You have heard, and apparently believe, that a bike tends to go where you are looking. That happens to be a true statement. But it is shorthand for reality. It implies that the bike is somehow aware of where you are looking and reacts accordingly. Nonsense. Failing that, it implies that your eyes are somehow connected to your handlebars or your brake lever. Nonsense.

Whether you are driving a motorcycle, a car, a truck, a bicycle, or a Cobra helicopter (that is not on auto-pilot), that vehicle tends to go in the direction you are looking - AND STEERING IT.

Normally, when you drive a vehicle, you look where you want to go - that is, straight ahead for the most part. Once you become an experienced driver you no longer tend to wander in your lane and no longer have to spend ANY conscious thought steering it in that direction. You are, in effect, using YOUR auto-pilot. When you wish to look in any other direction you turn off that auto-pilot and begin consciously checking that you are still on course - you visually confirm your path of travel is proper rather frequently while you 'steal a look' in that other direction. Furthermore, you make often substantial corrections to your steering as a result of making those confirmations because, not being on auto-pilot any longer, your vehicle TENDS to wander in the direction you are looking. In other words, YOU tend to steer where you look and the motorcycle simply does what it must do - it obeys.]]>