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Old 01-04-2010, 01:36 AM   #1 (permalink)
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Mountain bike guys say they're faster with LOW tire pressure

15 WAYS TO IMPROVE THE TUBELESS EXPERIENCE | News | Mountain Bike Action mountain bike, mtb, mountain bike racing, freeride, Downhill MTB, bike tests, MBA, Mountain Bike Action, Ask RC, XC mountain bike, trek, specialized, giant bikes, mantis, ellswo

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Old 01-04-2010, 02:07 AM   #2 (permalink)
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Reading further into it, there's a good reason... they're saying that the higher pressure makes the tire more susceptible to bouncing up and away from bumps in the road, so useless spinning of the tire occurs.

This isn't such a concern on, say, cars, where there is alot more weight per unit area of contact patch of the tire.
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Old 01-04-2010, 03:03 AM   #3 (permalink)
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Quote:
Originally Posted by Christ View Post
This isn't such a concern on, say, cars, where there is alot more weight per unit area of contact patch of the tire.
I don't have numbers right now but I suspect the loading i.e. psi in the contact patches would be quite similar...
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Old 01-04-2010, 04:35 AM   #4 (permalink)
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Frank Lee -

Quote:
Originally Posted by Frank Lee View Post
I don't have numbers right now but I suspect the loading i.e. psi in the contact patches would be quite similar...
It seems like this would apply to off-road driving conditions. Would the same article be applicable for Tour de France?

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Old 01-04-2010, 05:20 AM   #5 (permalink)
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Further investigation required!
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Old 01-04-2010, 06:03 AM   #6 (permalink)
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I've had a few mountain bikes and i do agree that higher pressures made traction worse. But i also agree that a mountain bike tire and a car tire are two very different animals. Also the conditions are very different......usually!

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Old 01-04-2010, 06:57 AM   #7 (permalink)
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Not again...

I dropped out of the last tire argument because some really ridiculous things were said in a very contentious manner, and my words were twisted into things I clearly didn't say. I didn't check back, but I doubt that anything was resolved.

You can bring random facts to the fore, but you can't make any of these anomalies apply to a real world FE argument.

For instance. when a top-fuel dragster approaches the start line, the tire appears to be very low on air. It's squat to the ground, and you can see the stress in the sidewall. But when the light goes green the centrifugal force of the spinning tire sends the tread to the outside very forcefully, and the car seems to jump in the air as it moves very quickly for a quarter mile. To apply any of this to hypermiling your daily commute just won't work.

The race conditions of the Tour de France and the Leadville 100 are very different from each other, but Lance Armstrong has won both. The latter on a flat tire.

http://www.singletracks.com/blog/mtb...lle-trail-100/

In a bicycle road race you do need traction, but the object is more one of as little RR as possible, and this is achieved by tire pressures well above 100lbs, resulting in a very tiny contact patch.

In a mountain bike race this would never work. The tires are knobby, not smooth, much fatter than road tires, and operating with much lower pressure.

So dragsters win races on tires that appear to be flat at the start line. Lance Armstrong wins the Tour de France on tires pumped up to 120-150lbs per square inch, and also wins the Leadville 100 on a rear tire that had maybe 2-3lbs in it. All interesting facts, but applying these facts to your daily commute to benefit your fuel economy will be even more interesting.
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Old 01-04-2010, 08:18 AM   #8 (permalink)
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I've raced with tubes and with Stans tubless. We ran at 45+ psi just like everybody else. No wonder I sucked.

There was a noticeable increase in rolling resistance with the same tire at 25 PSI then at 50 PSI. The big advantage was in flat protection and weight. You could take lines that were not available with tubed tires and the Stan were a little lighter which makes a big difference. I think this is like EPA testing. It's great in the lab but does not translate to real world mountain bike racing. If you look at most MTB race course there not real technical and mix in a lot of hard pack and jeep trails with a few rocky technical spots to keep it interesting. Depending on design of the tire, fat 2.0 vs skinny 1.85, at the end of the day usually the higher the PSI the faster. YMMV
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Old 01-04-2010, 08:08 PM   #9 (permalink)
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do these bikes have those stupid metal bars down the middle?!?
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Old 01-04-2010, 09:29 PM   #10 (permalink)
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offroad/low traffic concern, if you drive on riprap a lot then worth considering. if mostly relatively smooth pavement then you want inflated tires for efficiencies sake.

washboards are probably a more common case, but even then it is maybe %0.0000001 of the average vehicles miles (total swag).

A psi vs/"planing speed" test for washboards might be interesting to look at too, if anyone has a washboard nearby and is bored.

I've done the pedal low tires on pavement investigation, it arent efficient.

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Last edited by dcb; 01-04-2010 at 09:51 PM..
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