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Old 03-22-2012, 12:07 PM   #31
randyo
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Quote:
Originally Posted by dillon View Post
Running a tire at max PSI under less than max load will result in faster tire wear through the center and less rubber on the road. .
on a car, not on a bike, a single track vehicle leans in corners, if yer scrapin pegs over inflated or under inflated you'll wear the edgesm, if yer dronin in a highway, over inflated or unde rinflated, you'll still wear the center.

tire pressure in a bike regulates the amount of flex, or how hot the tire will get, not the contact patch
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Old 03-22-2012, 12:10 PM   #32
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Originally Posted by randyo View Post
tire pressure in a bike regulates the amount of flex, or how hot the tire will get, not the contact patch
the amount of flex (i.e., how much the tire deforms) determines the size of the contact patch.
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Old 03-22-2012, 02:54 PM   #33
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Quote:
Originally Posted by randyo View Post
E-mail the tire manufacturer ask THEM what you should be running for your bike and your weight
It amazes me that you can give good advice ...

Quote:
Originally Posted by randyo View Post
airing down for off road is a placebo
... and really off-the-wall advice in the same thread post.

Thanks for the entertainment.










So how does it work if I run a car tire on the back?
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Old 03-22-2012, 03:31 PM   #34
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Originally Posted by James Adams View Post
It amazes me that you can give good advice ...



... and really off-the-wall advice in the same thread post.

Thanks for the entertainment.

I guess he has limited experience off-road. Or maybe he considers off-pavement as off-road. Either way he could stand to learn a thing or two...
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Old 03-22-2012, 03:39 PM   #35
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Originally Posted by Bill Harris View Post
Depends on the tire manufacturer's recommendations and the tire pressure rise with riding.

The 1973 tag on my bike has 25/27 psi for the tire pressures, but that was for tires from that era. My current Avons recommend 32/36 psi and the bike feels better.

One rule of thumb we used to use back when was the "10% rule". Measure the tire pressures COLD. Go out and run them at highway speeds for 10-20 miles and measure the tire pressures HOT. If the pressure increase is less than 10%, your cold pressure is too high and the tire is not heating up enough. If it's more than 10%, your cold pressure is too low and the tire is heating up too much. Adjust the COLD pressures to get a 10% rise. The reason is sidewall flexing. Or so the theory was back then.

Otherwise,
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Old 03-22-2012, 03:42 PM   #36
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Originally Posted by DAKEZ View Post
I guess he has limited experience off-road. Or maybe he considers off-pavement as off-road. Either way he could stand to learn a thing or two...
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Old 03-22-2012, 03:49 PM   #37
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Originally Posted by randyo View Post
I'm very serious, no need to air down (radial tires)it does not make for better traction it makes for dented wheels if anything
Please give a reputable source supporting this claim. I think it has started a large enough controversy for this to be a reasonable request. No handwaving, just post a link.
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Old 03-22-2012, 04:18 PM   #38
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Originally Posted by opmike View Post
Please give a reputable source supporting this claim. I think it has started a large enough controversy for this to be a reasonable request. No handwaving, just post a link.

my source is nothing more than thousands of miles of personal experience (comparable terrain to the photo above)

I'm not one to believe something just cause its "on the internet", yes, I've experimented with "airing down" its like riding on a flat tire, limited control and I will not dispute the effectiveness of placebos
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Old 03-22-2012, 04:31 PM   #39
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Originally Posted by randyo View Post
my source is nothing more than thousands of miles of personal experience (comparable terrain to the photo above)

I'm not one to believe something just cause its "on the internet", yes, I've experimented with "airing down" its like riding on a flat tire, limited control and I will not dispute the effectiveness of placebos

You aired down too much.
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Old 03-22-2012, 04:37 PM   #40
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Originally Posted by antonac View Post
Am I the only one who thinks that this completely idiotic, and arguably dangerous? I run my KLR's front at 25-28psi cold with no load where they're rated for mid-30s, and I know of compatible tires with sidewall ratings well into the 40s.

Quote:
Originally Posted by msgroup aka James Davis
Stamped on the outside of many of your tires is a recommended tire pressure range. (At least an upper limit.) For longest tire life it is my recommendation that you strive to keep them at the higher limit of those recommendations (regardless of what your motorcycle owner's manual might say to the contrary.) Further, this pressure should be determined while the tires are cold - meaning, have not been used for a couple of hours.

http://www.msgroup.org/Tip.aspx?Num=009

They're talking about running this in the winter, no less, and give no other justification than "for longest tire life". On a safety site. I think maybe someone needs to have a word with these guys?
James Davis is a self appointed authority, but is mostly a jerk who has somehow gained acceptance in some circles as an authority. Take anything you learn from him with a grain of salt. You will find other myths in his and his followers' comments.

The maximum pressure is both for maximum load rating and for seating the bead of the tire. You do not want to exceed it obviously. Manufacturers have pressure ratings they prefer for ride and performance. In addition it can be dangerous to run too high a pressure for some riders. I ran some Yokohama sport tires at the 36 psi max on my Nighthawk S. I encountered tire patter on corners that were slightly rough. I dropped pressure to 32 and it went away. Seems that's a good pressure for other tires I've run for the way I ride. Racers in all motorsports vary pressures to suit their needs. There are also some ways to figure what works best.

As for Davis... well suffice it to say I told him to pull my membership from his jerk forum when he gave me crap about my posting of the kind of effort required to do a stoppie when those geeks were claiming sportbikes would flip over if you used the front brake hard and that they didn't stop well. He claimed I was advocating unsafe behaviour. I felt he was advocating ignorance, considering half of the bikes in their list of top ten stoppers were either sportbikes or sportbike based... imagine that. The guy is a pompous anus.
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Old 03-22-2012, 04:41 PM   #41
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Originally Posted by perterra View Post
You aired down too much.
so you really think I only tried it once at one low pressure, experimenting means trying all pressures and for more than a few miles at each setting
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Old 03-22-2012, 04:42 PM   #42
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Quote:
Originally Posted by Bill Harris View Post
Depends on the tire manufacturer's recommendations and the tire pressure rise with riding.

The 1973 tag on my bike has 25/27 psi for the tire pressures, but that was for tires from that era. My current Avons recommend 32/36 psi and the bike feels better.

One rule of thumb we used to use back when was the "10% rule". Measure the tire pressures COLD. Go out and run them at highway speeds for 10-20 miles and measure the tire pressures HOT. If the pressure increase is less than 10%, your cold pressure is too high and the tire is not heating up enough. If it's more than 10%, your cold pressure is too low and the tire is heating up too much. Adjust the COLD pressures to get a 10% rise. The reason is sidewall flexing. Or so the theory was back then.

Otherwise,
No it wasn't the tires in 1973. Those kind of recommendations were still common in to the late 80s. Until radials pretty much took over. The tire manufacturers will almost always recommend pressures closer to the max for their tires and the manufacturers of the bikes lower pressures to suit their testing and ride quality.

That test is a good one. I just read a note about the tires and that the tire pressure shouldn't go up more than a few psi, which would be about 10%.
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Old 03-22-2012, 04:44 PM   #43
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Quote:
Originally Posted by randyo View Post
my source is nothing more than thousands of miles of personal experience (comparable terrain to the photo above)

I'm not one to believe something just cause its "on the internet", yes, I've experimented with "airing down" its like riding on a flat tire, limited control and I will not dispute the effectiveness of placebos
You're arguing against things I never stated nor implied. However, you're more than welcome to attack straw men or chase down red herrings.

I asked for you to provide a source so that we can avoid these little anecdotes and personal appeals. Why? Because if I (or others for that matter) were to invoke my own off roading experience, I'd say that what you currently have posted in this thread with respect to tire pressures is incorrect. Because I've yet to find another individual that espouses the same views as you do on the subject. Tires, traction, tire pressure, etc. aren't in the realm of religion. If there's an increase in traction due to lowering of pressure (within reason), then there's a reason why. If this is not the case, then there is a reason why.
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Old 03-22-2012, 04:45 PM   #44
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Originally Posted by daveinva View Post
Hmmm. Since IME Davis backs up his "opinions" with empirical evidence and physics, I'm wondering if you could do the same?

Don't do it at his site though, He will threaten banning you... especially when he can not refute your data. Like his braking claims I mentioned earlier. I told him it was time to call it a day. I really wanted to tell him to stuff it. He's no special authority. He even disputed some of the late Dr Harry Hurt's data before.
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Old 03-22-2012, 04:53 PM   #45
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Originally Posted by randyo View Post
I'm very serious, no need to air down (radial tires)it does not make for better traction it makes for dented wheels if anything

Well, I'll tell you something - running a radial off road is pretty foolish in the first place. Thinking it is a real dirt tire is BS, with one exception to be mentioned below. Real off road quality tires are NOT radials they are bias belt anything else is only an adventure bike tire and not much of an off road tire.

As for running off road tires at lower pressure, if it's a placebo, why does every authority on racing and off road riding recommend about 18 psi in general and as low as 12 psi for knobbies, which are bias belt.

And why do trials riders run 3 psi in their RADIAL rear tires, the front are bias belt I think. Trials tires are the only radial that is true off road quality.
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