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brooks10
 Junior Member
25 Posts
Toronto, Ontario
Canada
Buell
XB12X
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 Posted - 11/03/2009 : 3:41 PM
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In Safety Tip#009 Mr. Davis recommends keeping tire pressure near the maximum limit of the tire for longer tire life. Are there any other benefits to higher pressures?
Thanks, Steve
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Twtinkertoy
New Member
10 Posts
Crump, Tennessee
USA
Kawasaki
Vn750
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Posted - 11/03/2009 : 8:54 PM
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Well, along with longer tire life, my rationale for near maximum tire pressures has to do with fewer stops at the gas pumps. The way I see it, higher pressure means less tread and sidewall deflection while under way. Less deflection in these areas means less rolling resistance, and less rolling resistance means greater fuel mileage for a given amount of gasoline.
This is a tactic that I've employed for many years on my automobiles, now my motorcycle, and shucks, even my riding mower. I
have always kept track of my fuel mileage, and can attest that firmer tires (higher pressures) do indeed maximize that mileage.
The downside to this is a harsher ride, but I'm so cheap that I just slow down so the bumps aren't as hard! So, bottom line---fewer tires to buy and fewer stops at the pumps. Win, win.
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galileo
Standard Member
128 Posts
Florence, Co
USA
Suzuki
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Posted - 11/04/2009 : 6:53 AM
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quote:
Originally posted by Twtinkertoy
Well, along with longer tire life, my rationale for near maximum tire pressures has to do with fewer stops at the gas pumps. The way I see it, higher pressure means less tread and sidewall deflection while under way. Less deflection in these areas means less rolling resistance, and less rolling resistance means greater fuel mileage for a given amount of gasoline.
This is a tactic that I've employed for many years on my automobiles, now my motorcycle, and shucks, even my riding mower. I
have always kept track of my fuel mileage, and can attest that firmer tires (higher pressures) do indeed maximize that mileage.
The downside to this is a harsher ride, but I'm so cheap that I just slow down so the bumps aren't as hard! So, bottom line---fewer tires to buy and fewer stops at the pumps. Win, win.
I run a high tire pressure in my cars and it does improve gas mileage and tire wear. But on my bikes, I use the recommended tire pressure.
It's debatable if increasing tire pressure on a motorcycle would improve wear. A car tire is basically flat. Increasing tire pressure does prevent the edges from wearing as quickly. However a motorcycle tire is rounded. "U" Increasing pressure may cause less tire to be on the road and the center could wear more quickly. It might also cause cupping on the tire, especially on the front tire.
Tires are a major part of the shock absorbtion on a bike. Aside from feeling it more on your butt, there may be control issues with a tire inflated above that recommended in the owner's manual. For instance, hitting a pothole where the exit is slightly angled would likely move the contact patch forward more on an overinflated tire. This could result in the bike becoming unstable. Or it could perhaps cause the front fork to bottom out causing damage.
Sometimes the recommended pressure is much less than the maximum sidewall pressure. For instance, on one of my bikes, the recommended front tire pressure is 29 psi and the max sidewall pressure is 36 psi. However, the bike only weighs 442 pounds and the CG is pretty far aft. In some situations, increasing the pressure might cause the tire to lose contact with the road if I hit some bumps.
My feeling is the manufacterers spend a lot of time testing bikes and along with that find the proper tire pressure. It's said that the design of a bike begins with the tires. I'd rather not become a test engineer and mess with that for the sake of a little better gas mileage and the possibility of a little better tire wear. The safety considerations might not be apparent until too late.
I've included a lot of language to try to avoid a declarative statement. My opinion is the manufacteror knows best and I don't want to mess with it. Others have different opinions. |
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Night Train
Moderator
942 Posts
[Mentor]
Sydney, Nova Scotia
Canada
Harley-Davidson
Softail and Touring
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Posted - 11/04/2009 : 8:09 AM
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I would think that the maximum recommended air pressure as stated on the sidewall of the tire is rated by the Tire Manufacturer in respect to the capabilities of the tire.
The recommended tire pressure as stated by the Vehicle Manufacturer relates to the capabilities and handling of the vehicle.
I would think the problem would arise if the Vehicle Manufacturers recommended tire pressure exceeded the Tire Manufacturers recommended tire pressure. However, I don't recall ever seeing that situation in a real life scenario. |
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Niebor
Advanced Member
2793 Posts
[Mentor]
Highlands Ranch, Colorado
USA
Harley-Davidson
03' Superglide
Peer Review:
1
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Posted - 11/04/2009 : 12:22 PM
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It is my opinion the range between the vehicle manufacturer and tire manufacturer sidewall rating is fair game to experiment a bit. I advise no more than 1 psi adjustments, and riding at the new pressure for a good long while before making further adjustment.
I'm told I don't weigh enough to be riding a Harley. They say riders over 220 lbs never have problems with front end wobble. I know, sounds way off track, I'll redirect.
Being me, I tend to first experiment at the extremes, then narrow the gap toward a real setting. Having done that, I found running at maximum sidewall rating to be one of few pieces of bad advice I ever received here. The frame rating, not 1 psi more, and the lowest rear shock preload gives me the best ride and control of all the settings I tried. Increasing either, only slightly, produces a marked increase in rear wheel slide. Pretty easy to tell the difference, this time of year. 
As to fuel economy, my right hand habits alter that number far more than tire pressure. I have seen 58 mph on the high end, 29 mpg on the low. These days, I usually range from 46 to 52. Getting old I guess.  |
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Night Train
Moderator
942 Posts
[Mentor]
Sydney, Nova Scotia
Canada
Harley-Davidson
Softail and Touring
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Posted - 11/04/2009 : 1:07 PM
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quote:
Originally posted by Niebor
[br
I'm told I don't weigh enough to be riding a Harley. They say riders over 220 lbs never have problems with front end wobble.
I don't know why one would say that. When you look at the specs on any of the Harleys they are done with the rider profile being 180lbs. I would think if your front end is going to wobble it shouldn't matter if your rear end is hanging over both of your side covers  |
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Niebor
Advanced Member
2793 Posts
[Mentor]
Highlands Ranch, Colorado
USA
Harley-Davidson
03' Superglide
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Posted - 11/04/2009 : 2:03 PM
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quote:
Originally posted by Night Train
quote:
Originally posted by Niebor
[br
I'm told I don't weigh enough to be riding a Harley. They say riders over 220 lbs never have problems with front end wobble.
I don't know why one would say that. When you look at the specs on any of the Harleys they are done with the rider profile being 180lbs. I would think if your front end is going to wobble it shouldn't matter if your rear end is hanging over both of your side covers
LOL, Well, I come in about 15 lbs short of that spec. All I know is the front is far more... twitchy? at maximum pressure and preload. Rear pressure and rear preload both seem rather pronounced in the front end equation.
Don't know, ask the big guys if they've ever been thrown off. I suspect you'll come to the same conclusion I did.
I've have decided the bike is safe to ride. The exception being higher speeds into high headwinds. Facing that, I either slow down or turn around. Being a recreational rider, I usually have the option to simply turn around. |
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Gs82Seca650
Moderator
1849 Posts
[Mentor]
Southern, PA
USA
Yamaha
1982 XJ 650 R Seca
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Posted - 11/04/2009 : 2:11 PM
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quote:
Originally posted by Niebor
I found running at maximum sidewall rating to be one of few pieces of bad advice I ever received here.
Then we'll agree to disagree my Friend. I run my seca front and rear at 40psi, the maxium sidewall pressure stated on my supposed "junk" Chen-Shin Chinese tires (that were on the bike when I bought it 3-4 yrs ago.
I've never had a problem and I actually like how the bike handles with the tires a bit on the firmer side. Never had any wet traction issues either.
To each his or her own....do what you feel is best, but I run ALL of my vehicles tires at the MAXIMUM COLD sidewall pressure for MAXIMUM treadwear life and best possible fuel economy.
Again, this is only MY opinion, if yours differs, that's just fine!  |
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Niebor
Advanced Member
2793 Posts
[Mentor]
Highlands Ranch, Colorado
USA
Harley-Davidson
03' Superglide
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Posted - 11/04/2009 : 2:57 PM
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I should have called out the numbers.
The frame calls out 29F-32R, solo rider no gear. The stock H-D/Dunlops show 41 psi max. Because of advice I'd received here and elsewhere, I started at the top and worked my way down. I made downward adjustments over about a year. I rode it for several months at the bottom of the range. Then, I increased both tires by 2 psi. I wound up bleeding off that 2 psi, and have maintained recommended pressures since. I've been riding this setup for about six months now.
I would add that I have seen no decrease in tire life whatsoever at the reduced pressures. Though, in fairness I have been easier on tires in recent years. It could be they are indeed wearing faster, and a cleaner and slower riding style has offset that loss. |
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toolmaker
New Member
17 Posts
Austin, TX
USA
Kawasaki
ninja 250
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Posted - 11/17/2009 : 10:05 PM
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Um, here goes...
The sidewall rating is the max air pressure that the tire will hold. It's meant to be used when the tire is at max load, usually temporarily.
Sure, your mpg may be better, less rolling resistance, but your traction suffers, possibly a lot.
What to set your pressure to? Oddly it appears to be different for cars and motorcycles. In a car you start with the car maker's recommendation (always used to be too low -- better ride, but worse handling due to tire squirm)and add air until you find the handling you like. And on a car you can look at the wear pattern; wear in the middle, too much air, wear on both edges, to little.
On a bike, according to every source I've read, you start with maker's recommendation and lower the pressure until you get the handling you want. It seems that squirm is not an issue on bike tires and the bigger contact patch give more traction. (Boy, I hope that's right or Davis will flame my ass).
It's probably a good idea to adjust pressure to weight. One up vs two up for example.
I would never compromise handling for economy.
Best,
Jerry |
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James R. Davis
Administrator
14193 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 11/17/2009 : 11:13 PM
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Your comments about tire traction are simply wrong. The amount of traction your tire provides is almost identical whatever size its contact patch is,
I also disagree about starting at bike manufacturer's settings and decreasing from there. In fact, I start at the tire manufacturer's max rating and have stayed just below that for at least 30 years because of best tire life, longer durations between having to add air without having inadvertently ridden on dangerously low pressure, and because I frequently carry passengers. |
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galileo
Standard Member
128 Posts
Florence, Co
USA
Suzuki
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Posted - 11/18/2009 : 4:36 AM
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quote:
Originally posted by James R. Davis
Your comments about tire traction are simply wrong. The amount of traction your tire provides is almost identical whatever size its contact patch is,
I also disagree about starting at bike manufacturer's settings and decreasing from there. In fact, I start at the tire manufacturer's max rating and have stayed just below that for at least 30 years because of best tire life, longer durations between having to add air without having inadvertently ridden on dangerously low pressure, and because I frequently carry passengers.
James, can you state with certainty that riding with max tire pressure is good for all bikes? I have one where the recommended pressure is 29 psi on the front and the sidewall is 36. Increasing the pressure seems to make the ride a lot harsher and could be problematical in curves if one hits a good bump. I agree the traction the tire has doesn't change much with tire pressure, unless it doesn't maintain as good contact with the road.
On a different bike, I find if I go above the manufacturer's recommendation, the front tire starts to cup sooner. I'm on about my 9th set of tires on this bike, so I've had a lot of time to experiment.
Would it be reasonable to suggest that one tries increasing pressure a pound or two at a time and see what happens rather than saying max sidewall is best for all bikes? |
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dhalen32
Moderator
547 Posts
[Mentor]
Omaha, NE
USA
Yamaha
FJR 1300
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Posted - 11/18/2009 : 6:29 AM
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I'm with Niebor on this one. A blanket statement of running at maximum sidewall pressure may work for Jim but is not necessarily best (or correct) for everyone.
If one has the patience, experimenting as Niebor has suggested is probably the best general advice: Start at maximum pressure molded into the sidewall of the tires and then bleed off one psi and ride for a few weeks or months. Repeat until you find the optimum pressure for you and then check frequently to maintain that pressure.
There are a few caveats of which to be aware: 1. Don't bleed air to the point that you are below the bike manufacturer's recommendations for passenger count and load. Underinfalted tires are dangerous. Higher pressures generally result in lower operating temperatures, longer wear and higher fuel economy. That's Jim's advice talking. 2. Take the time to adjust tire pressures according to the situation. If you are riding two up and carrying lots of baggage on a long tour then you should be at or near that maximum molded into the tire's sidewall. If you are riding by yourself on a twisty, bumpy canyon road then maximum tire pressures could be a big mistake. Read your owner's manual, experiment using the Niebor method and then make the right choice for you.
Dave |
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James R. Davis
Administrator
14193 Posts
[Mentor]
Houston, TX
USA
Honda
GoldWing 1500
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Posted - 11/18/2009 : 7:32 AM
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quote:
James, can you state with certainty that riding with max tire pressure is good for all bikes?
The bike's manufacturer makes recommendations about tire pressure that are meaningful for OEM tires only. When you replace the original tires with anything else but the identical OEM tire, those recommendations are no longer valid.
The tire manufacturer, however, embosses a maximum SAFE pressure for that tire. It also tells you what the tire is rated for in terms of max speed and max carrying capacity.
If the tire manufacturer says that you can use up to 36 psi in their tire, you can do so, or you can use LESS air pressure (never higher).
For those who claim to be able to tell the difference in handling with as little as a 1 psi change in pressure, I am doubtful. For those who claim that using at or near max pressure in their tires is not for them, I agree.
For those who think that using near max PSI causes cupping ... I suggest that the odds are far greater that you have the wrong tire for the bike and/or your shocks need work than that it is caused by high pressure in the tires.
I can say with certainty that using at or near max rated air pressure is not dangerous. 'Good for all bikes'? Do you like vanilla or chocolate? |
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galileo
Standard Member
128 Posts
Florence, Co
USA
Suzuki
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Posted - 11/18/2009 : 8:11 AM
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quote:
For those who think that using near max PSI causes cupping ... I suggest that the odds are far greater that you have the wrong tire for the bike and/or your shocks need work than that it is caused by high pressure in the tires.
I use the recommended tire. There are only 2 choices for this bike and the one that comes with it works the best. The other wears out very quickly. The shocks are fine.
It's fair to agree with the concept of experimention with increasing pressure up to the max sidewall as long as it's done in small increments. I've read a lot about this on forums specific to my bikes. Some swear by it. Others swear at it.
I like chocolate.
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Gs82Seca650
Moderator
1849 Posts
[Mentor]
Southern, PA
USA
Yamaha
1982 XJ 650 R Seca
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Posted - 11/18/2009 : 9:00 AM
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quote:
Originally posted by James R. Davis
[quote]
I can say with certainty that using at or near max rated air pressure is not dangerous. 'Good for all bikes'? Do you like vanilla or chocolate?
100% Correct. |
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toolmaker
New Member
17 Posts
Austin, TX
USA
Kawasaki
ninja 250
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Posted - 11/18/2009 : 9:30 AM
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James,
I probably should have mentioned my own qualms regarding lower pressures. Coming from a performance car perspective it just doesn't seem right.
However, here's a sampling of some quotes on the subject:
""""""""""""""""""""""""""""""""""""
http://www.sportrider.com/tech/tire...e/index.html
For optimum performance while heeled over on the track, tire manufacturers usually recommend running pressures lower than those reserved for the street. Why? The lower pressure allows for a larger contact patch and therefore more grip in the corners.
http://en.allexperts.com/q/Motorcyc...ressures.htm
From the manufacturer's pressure recommendation, you can customize your tire pressures to your liking. Lower pressures will put more rubber on the road and warm up faster, but will make the bike harder to steer and turn. Higher pressures will put less rubber on the road, warm up slower, but the bike will turn much more easily.
http://faq.ninja250.org/wiki/What_t...should_I_use
Generally speaking, more pressure gives you less grip, and less pressure gives you better grip. But you can go too low, and then the tires overheat and get greasy and slick. Also, the more weight you have on the bike, the higher your air pressure should be. Underinflated tires with lots of bike weight will become hot and dangerous quickly.
""""""""""""""""""""""""""""""""""""
While I don't race and have never been on a track, I want the best performance (which correlates with safety in my mind) I can squeeze out of my bike.
BTW, even if they have the physics wrong, it appears that they agree that lower pressure (within reason) gives better track times.
One thing I strongly disagree with is pushing tires near or to the max pressure. I've never seen any reliable source advocate that.
Best,
Jerry |
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gymnast
Moderator
2211 Posts
[Mentor]
Meridian, Idaho
USA
Harley-Davidson
Sportster Sport
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Posted - 11/18/2009 : 9:36 AM
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| On my HD Sportsters running 2 up most of the time, I run 40 PSI rear and 35 PSI front and check it often. The tires are Dunlop Elite 3s on my '97 and Metzler ME99s with tubes on my '78. I find these tire pressures to be satisfactory on both bikes and do not change them for solo riding. Rider weights, 2 up 180+125+gear(25?)= 330 or so. |
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scottrnelson
Advanced Member
4748 Posts
[Mentor]
Pleasanton, CA
USA
Ducati
ST2, 888, + XR650L
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Posted - 11/18/2009 : 10:28 AM
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quote:
Originally posted by toolmaker
However, here's a sampling of some quotes on the subject:
[...]
BTW, even if they have the physics wrong, it appears that they agree that lower pressure (within reason) gives better track times.
I'm not disagreeing with you, but pointing out a bunch of internet sources doesn't necessarily make it correct. Some things seem to be "common wisdom" based on no actual facts.
I would like to see someone do a study on motorcycle traction versus air pressure in a street environment (i.e., not while taking a bunch of hot laps at a race track).
I know that Car and Driver magazine did some street tire tests in the 70's and they found that they got the best traction at the highest recommended pressures for all of the tires that they tested. They also found that in slick conditions lower pressures gave more traction. But I don't know if those findings translate in any way to motorcycle tires. |
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The Meromorph
Advanced Member
596 Posts
[Mentor]
White House, TN
USA
BMW
R1100R
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Posted - 11/18/2009 : 9:20 PM
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James has a particular situation of riding a heavy bike that is near the load limits of the available tires. Since those load limits occur at the tire manufacturers Max Pressure, he naturally finds the range of safe pressures to be very limited. Within that limited range, it is no surprise that the 'best' pressure turns out to be at one of the limits, actually the upper limit. It is possible that if the particular tires had a higher max pressure, he would find the 'best' pressure to be higher than his current max pressure. He is accurately reporting his experience given his bike, and the available tires for it.
So, also, are those who report an apparently contradictory result, from bikes with a total load far below the tires' rated capacity.
This is where theoretical design meets the real world of available components. Racing is a somewhat different 'real world' where specialized 'one-off' components can often be used, so generalizing from racing experience to the street is of little use.
The size, and shape, of the contact patch, within normal limits does not affect the available traction, but, at the limits, it can have significant effects on the limits (mainly due to tread shearing and heat effects). Racing is usually pressing the limits (or should be), but you should never be at the limits on the street, so, again, racing experience is not useful on the street in this case. |
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bachman1961
Advanced Member
952 Posts
[Mentor]
colorado springs, co
USA
Honda
CB750 NightHawk
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Posted - * Today * : 3:38 AM
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Where James says the manufacturer of the bike bases meaningful tire psi on the OEM tires, and Niebor illustrates his latest tire choice is a variation of 10-12 psi from the frame sticker, it seems too wide of a range to toy with.
I'd assume the starting point is at or near the tires rated maximum and I wouldn't be comfortable fussing with it beyond 12-15 percent. That puts a tire rated at 41 psi down to 35 psi as a minimal set point and around my threshold of being comfortable with extending the testing range.
This mirrors the situation with my bike where my newer tires are rated 39 and 41 psi and I've varied pressures to 34-35 range. Typically, I run them 2-3 psi shy of the max ratings. I don't have enough road experience to have rated the handling changes but I can attest to the fact that 2 psi makes a difference in the ride and thump factor. Maybe it's a placebo, but I think (in my case) -2 psi is a good balance between semi rigid and plush ride.
The Meromorph comments rings true to my thoughts on some variables;
Bike design, suspension, load rating, geometry, rubber compound in the tires themselves, weight of the rider, tire profile etc.... each bike design has it's own personality and handling characteristics and once the OEM tires are smoke, it's a whole new ball game (beyond the manufacturers intentions).
Ideally, we could read tire reviews categorized by the bike itself, riding style, and showing performance, wear, traction and prices among other criteria.
I like Oreos , are they chocolate or vanilla ?
~brian
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