All Things Motorcycle - Physics and the theoretical

en-us Fri, 20 Nov 2009 16:53:55 -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 - Question about centrifugal forceJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=11082&REPLY_ID=107800Physics and the theoretical Mon, 16 Nov 2009 17:34:58 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=11082 Centrifugal force is as real a force as any other. It IS an inertial force, as you say. Though it feels like it is pushing you 'outward', it is actually, again as you say, simply trying to keep you moving in the same direction you were in before turning.]]>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 15:13:26 -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 - Total Time to Full Load BrakingJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10881&REPLY_ID=105932Physics and the theoretical Mon, 21 Sep 2009 14:26:06 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10881 Whittlebeast,

It's obvious that you really know your stuff. Why not start some active discussion about bike mods in the Add-ons/Customization forum to get your experience and knowledge a wider audience? This particular forum is read by a small subset of our members as it is usually dealing with theoretical as distinct from practical issues.
]]>Physics and the theoretical - Lean angle data recordersportyhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10382&REPLY_ID=105863Physics and the theoretical Sat, 19 Sep 2009 19:30:07 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10382 Now, has anyone come to the realization that
with a 3-axis (orthogonal) accelerometer,
orientation of the sensor becomes meaningless?

Pop quiz question #1: calculate the acceleration.

-W
]]>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 - Brake lever force vs speedDnchttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=10818&REPLY_ID=105406Physics and the theoretical Sun, 06 Sep 2009 10:36:28 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10818 I do much the same thing when driving the car or riding the bike. Mostly, I think, because I'd rather do as much of the braking as possible before I reach the stopping point; somewhat of a habit from driving on icy roads much of the year. Brake early; brake often [8D]

I don't think the front wheel will lock as you near the end of the stop, unless you've been increasing the braking force past the traction limit as you stop. The jerking at the end of the stop isn't the wheel locking, it's the suspension decompressing now that the deceleration is over.]]>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 Wed, 17 Jun 2009 13:28:41 -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: F_t = s A_t [kPa], where s is the "shear stress" in the soil and A_t 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=101183Physics and the theoretical Sun, 07 Jun 2009 00:17:46 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=10336 I'm glad I read this post.

I was interested in traveling along the Equator next year but it's obviously quite windy there.

~b

(spelling)]]>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.]]>Physics and the theoretical - Dry clutches and The Friction ZoneThe Meromorphhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9919&REPLY_ID=97848Physics and the theoretical Tue, 31 Mar 2009 21:02:52 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9919 Well, it would seem we have a consensus of everyone but me. [:I]

I now know the focus of a goodly portion of my PLP for a while. [:)]

Thank you all.]]>Physics and the theoretical - CoG Height and Flickability?Andrew Dresselhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9348&REPLY_ID=97137Physics and the theoretical Wed, 18 Mar 2009 08:58:51 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9348 Here's more information that might be interesting. Cossalter describes a Koch Index; apparently defined by J. Koch in his 1978 disertation in Berlin, but not used much since; that is the ratio of peak steering input torque to the product of forward speed and the peak roll rate. Cossalter says it "is mainly influenced by center of mass height, front wheel intertia, front frame inertia with respect to steering axis, frame inertia with respect to rolling axis and yaw axis." Touring bikes have a Koch Index of about 3, sport bikes between 1.5 and 2, and scooters of about 0.5.]]>Physics and the theoretical - Wheel balancing beads, scam or not....bkikkerthttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=4031&REPLY_ID=96485Physics and the theoretical Sat, 07 Mar 2009 14:40:26 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=4031 A friend of mine uses them in his motorcycle tires and he claims they work just fine and do not make any noise.]]>Physics and the theoretical - 2 wheel drive KTMrkfirehttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9302&REPLY_ID=96060Physics and the theoretical Wed, 25 Feb 2009 12:34:37 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9302 Sure it exists, 2wd that is, Rokon has been making them for over 50 YEARS! lol]]>Physics and the theoretical - Camber thrust and slip anglegreywolfhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9613&REPLY_ID=95591Physics and the theoretical Sun, 15 Feb 2009 18:28:22 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9613 I had Dunlop trigonic tires on my Can-Am 175 TNT repli-racer. They dropped me straight up with a locked front brake and low sided in a turn. Neither case should have been anywhere near breakaway force. They were the worst tires I ever had. Maybe the 175 didn't have enough to warm them up since the cafe racer types raved about them.]]>Physics and the theoretical - Why's my bike front & back wheels aren't the same size?Worahttp://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9653Physics and the theoretical Fri, 13 Feb 2009 10:08:30 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9653 I ride my bike for half a year now and really familiar with it.
It has very good reliability for a C.V.T. bike(automatic), the top speed I ever did was 112kmh(on freeway),I'm a bit of speed freak but I dislike the street racers, they are stupid.

But I still have many things I don't understand, my bike is a 115cc scooter http://en.wikipedia.org/wiki/Yamaha_Mio, it was built with 70/90 and 80/90 tires, the rear is a bit bigger. What is the different between the feeling and control from the same sized tire bike?
And what is the limit of leaning angle? I leaned to about 30 degrees at 60km/h once and feel like I would slip off the curve.
]]>Physics and the theoretical - "Heads Up"gymnasthttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9166&REPLY_ID=95402Physics and the theoretical Thu, 12 Feb 2009 16:53:42 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9166 That is a really original idea and an elegantly simple solution. Thanks for the link.]]>Physics and the theoretical - Interesting paper by Sharpwaxclanhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9365&REPLY_ID=94120Physics and the theoretical Wed, 21 Jan 2009 18:40:15 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9365 I did - is most all the data/work that "old"? Professor Sharp's work is about the only professional work that is fairly recent I could find. As an interesting aside, see below.

Professor Robin Sharp from the University of Surrey has attracted a lot of interest in his work modelling the optimum golf swing. ("On the mechanics of the golf swing", Proceedings A of the Royal Society, published on-line, 5 November 2008). Articles have appeared in the BBC News, in papers such as the Telegraph and the Daily Mail and Robin has been interviewed on radio programmes3 such as Drive Time and Talk Sport. Professor Sharp found that contrary to popular belief the wrists are not critical to the perfect, long-distance golf swing but rather that how and when the power develops is key to achieving distance. Based on a golfer's physical dimensions and strengths, and using their known top-of-the-backswing positions, Robin has calculated how to achieve the maximum club-head speed, for a standard driver, at impact with the ball. Positions of shoulders, arms, grip and club shaft are shown at 10 ms intervals through the swing for Bernard Hunt's best swing in the figure below. The model shows that Bernard's drive distance could have been improved by increasing the shoulder torque quickly to the maximum value, and then maintaining it throughout the rest of the swing, while initially holding back with his arms and wrists. The timing of the switch from holding back to hitting through with the arms is the most critical feature of the swing.

]]>Physics and the theoretical - Traction, lean angle & speedJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9379&REPLY_ID=93929Physics and the theoretical Mon, 19 Jan 2009 09:17:43 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9379

quote:
In this way, you increase the lateral force for the same lean angle.

Please!

Your bike's lean angle has nothing to do with lateral force. That is determined by speed and radius of the turn you are making. When you declare a 'fact', please take care that it really is a fact. When you speak of 'lateral force', think in terms of 'centrifugal force'.]]>Physics and the theoretical - Theoretical Cornering QuestionPike Bishophttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9455&REPLY_ID=93830Physics and the theoretical Sat, 17 Jan 2009 11:38:47 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9455 Well, I have to admit that I'm more mystified now than I was before I asked the question, but I thank you all for taking the time to reply.

I guess I need a lot more "seat time" to understand all this stuff. There are so many forces and phenomena at work on moving motorcycles that I suspect even people with Ph.D.s in physics argue over what exactly is going on! [:o)]

Thanks again.]]>Physics and the theoretical - Aerodynamic drag and liftwaxclanhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=955&REPLY_ID=93768Physics and the theoretical Fri, 16 Jan 2009 13:32:49 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=955 Great topic - I had never considered wind resistance resulting a weight transfer effect in the same sense acceleration does.]]>Physics and the theoretical - Weight and SteeringBearyhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9426&REPLY_ID=93619Physics and the theoretical Tue, 13 Jan 2009 14:31:15 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9426

quote:
Originally posted by Mikeydude

Is is possible that a weight difference on one side of the handle-bars would cause a bike (or any 2 wheeled vehicle) to drift off track?
cause the bike to drift left or right (countersteer)?

Yes, the way your front suspension is designed, the wheel will turn into the lean of the bike. Of course it is also designed to pull itself back on track as well, but a constant pull to the left will turn the front tire ever so slightly to the left.

Harleys have a reputation for this because the heavy primary drive on the left side hangs out just enough to make the bike left side heavy. You wouldn't know it if you don't take your hands off the bars. And for some reason not all Harley drivers feel the problem. I do feel it on my road king.

I used to wonder if the primary really could make that much difference, then a few months ago I sat on a custom harley that was so well balance that you could almost stand it up with just your little finger. They got it that way by moving transmission drive, belt and rear wheel belt pulley to the right side to balance the weight of the primary drive.

Also, there are a few folks who found that their clutch cable pulled on the engine guard thus making the pull to the left.

If you still wonder if weight can do this, get a friend willing to ride as a passenger and have them hold a ten pound dumbbell. Ride about 20 mph and have you buddy slowley hold the dumbbell out arms length. You should feel the change.

Beary]]>Physics and the theoretical - Crowned roadsSkootchNChttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9414&REPLY_ID=93470Physics and the theoretical Sat, 10 Jan 2009 21:05:50 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9414 I imaging it would depend on the crown percentage.... a steep crown, would present itself towards the left side of the tire.. similar to "counter-steering"... but as with ANY man... I'm often wrong..... just ask Mz Beckie]]>Physics and the theoretical - GPS/speedometer riddleGeotiggyhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9378&REPLY_ID=93180Physics and the theoretical Tue, 06 Jan 2009 14:26:43 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9378

quote:
Originally posted by Pike Bishop

IIRC, the GPS on my boat regularly shows elevations ranging from -20' to +40' on the Atlantic Ocean. [:u]

That's entirely posible since the GPS system considers the earth a sphere and the rise and fall of the waves could skew the 'surface' calculations by 10'-20' fairly easily.

The most accurate GPS units I've worked with show changes every 4'-6'. Altitude assessments are calculated based on the number of satelites the unit can 'see'. (This was a major limitation in the early days of GPS, but have gotten MUCH better as more satelites are put in orbit.) Even with a potential variant of only 4' the differential can grow very quickly. As a result, showing your 'altitude' as -20 (even on a calm day at sea) is not out of the question, Assuming your boat is on the surface and not a developing coral reef. [:I]]]>Physics and the theoretical - GasTank Implodedscottrnelsonhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9321&REPLY_ID=92537Physics and the theoretical Sat, 27 Dec 2008 08:00:35 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9321 Didn't you already post this once in the General section?

Let's make sure we don't carry on two separate discussions now. All replies should go with the first post, not here. Maybe a moderator can move the other post to this section for you.]]>Physics and the theoretical - Re: Hanging Offonesportbikeriderhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=1857&REPLY_ID=92414Physics and the theoretical Tue, 23 Dec 2008 07:10:21 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=1857 Can't be an official Yamaha video. That riding posture sucks![88]

While I see his butt shift a few times in the beginning, it doesn't look like he's hanging off to me.

This is what I consider hanging off
http://jp.youtube.com/watch?v=njFgELIEcr4]]>Physics and the theoretical - Do scale model bikes steer in the same way as our full scale bikes?scottrnelsonhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9232&REPLY_ID=91720Physics and the theoretical Thu, 04 Dec 2008 10:23:26 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9232

quote:
Originally posted by dogdoc427

Mine did not have the "outriggers" that some of the ones in the links do so when it fell over I had to "go fetch" and start over. It got tedious quickly.

More than half of the time I was able to get my Jeremy McGrath Stunt Cycle moving around enough to get it back up and running when it fell over. But I couldn't count on doing it when I needed it. That one also had a gyroscope inside the rear wheel to help it balance once it had been moving a bit.]]>Physics and the theoretical - Weight biasscottrnelsonhttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=9125&REPLY_ID=91719Physics and the theoretical Thu, 04 Dec 2008 10:18:00 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=9125 While we're on the subject of weight distribution, this morning I was reading about the new Aprilia RSV4 in the January 2009 issue of Cycle World magazine. The RSV4 was designed specifically to compete in World Superbike racing, with a 1000cc V-4 engine and a frame based on Aprilia's 250cc MotoGP racer that has won a number of world titles.

What I found interesting is that the article noted the 51%/49% front/rear weight distribution and noted that the seat was positioned a bit more forward than is normal allowing this weight distribution to be maintained with a rider aboard.

So there is at least one motorcycle out there that comes pretty close to even weight distribution with the rider on the bike.

And what happened to all of you who were going to weigh your bikes? Am I the only one who actually went to the trouble of doing that?]]>Physics and the theoretical - weighting the pegsJames R. Davishttp://www.msgroup.org/forums/mtt/topic.asp?whichpage=-1&TOPIC_ID=7045&REPLY_ID=91591Physics and the theoretical Mon, 01 Dec 2008 09:36:03 -0500http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=7045

quote:
1. Gyroscopic precession also tends to turn the front wheel in the direction of a lean in response to that lean just as trail does, through probably with different torque and rate of application.

2. As for the gyroscopic effects of the rear wheel and transverse mounted engine, I'm in the Cossalter camp which states "the gyroscopic moment [of the spinning wheels] tends to make the motorcycle yaw to the right, and this is balanced by the lateral resistance exerted on the wheels by the ground." So I don't believe they generate any resistance to leaning.

Let's see if we can add some clarity here.

Precession (gyroscopic force) can cause roll or yaw. Roll concerns the whole motorcycle and is what we usually call lean. Yaw is what we normally call a change of direction.

Spinning wheels and engine parts (if mounted transverse) will tend to right the motorcycle when it leans to one side or the other. That's a roll moment at play.

When a motorcycle is moving in other than a straight line it is causing a yaw moment to exist via those spinning components. The yaw moment is felt at the front wheel and tries to straighten that wheel (the rear wheel is constrained), just as the righting force caused by trail does. The yaw moment and the roll moment are both stabilizing.]]>