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post #1 of 6 Old 06-05-2007, 6:19 AM Thread Starter
 
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Tyre pressures

I need some education here,

We all talk about tyre pressures and letting air out if we ride them heavy/ hot because of various reasons. Tyres expanding etc
Now my question is (and can anyone tell me) what exactly is the standard tyre operating temp

I live in the Middle East and average ambient temp during summer months is around 45 DegC. I ride my 929 every day to and from work and aslo on weekends (when I take it out for a real thrashing).
I have always had the pressures at 42/ 36 rear front respectively. Never had any slips (to date), apart form the usual diesel etc, and as I said I'm on the limits of the tyres on bends.

So why should I lessen the pressure?

It all works for me?
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post #2 of 6 Old 06-05-2007, 9:08 AM
 
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Re: Tyre pressures

Blimey that hard.... I usually keep both around 30ish but thats in shitty cold UK climate.
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post #3 of 6 Old 06-05-2007, 9:51 AM
 
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Re: Tyre pressures

from what i have read and personal experience, tire pressure seems to be a matter of personal preference for the commuter/weekend warrior. i run 35psi front and rear and like that. i also ride everyday to work. the stock isn't far from that, so if you like it, leave it alone.
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post #4 of 6 Old 06-06-2007, 4:19 AM Thread Starter
 
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Re: Tyre pressures

Start with the bike manufacturer's recommendation in the owners manual or under-seat sticker. This is the number they consider to be the best balance between handling, grip and tyre wear. Further, if you're running alloy wheels on poor pavement, consider adding 2 psi to the recommended tyre pressure just to reduce the likelihood of pothole damage. Just as you would for a car, increase the pressure 2 psi or so for sustained high speed operation (or 2-up riding) to reduce rolling friction and casing flexing. Check your tyre pressure regularly as they say.

In order to get optimum handling a tyre has to get to its optimum temperature which is different for each brand of tyre. Most of us don't have the equipment needed to measure tyre temperature directly so we measure it indirectly by checking tyre pressure since tyre pressure increases with tyre temperature. Tyre temperature is important to know because too much flexing of the casing of an under-inflated tyre for a given riding style and road will result in overheating resulting in less than optimum grip. Over-pressurizing a tyre will reduce casing flexing and prevent the tyre from getting up to the optimum operating temperature and performance again suffers. Sliding and spinning the tyres also increase tyre temperatures from friction heating.

A technique for those wanting to get the most out of their tyres on the street is to use the 10/20% rule.

First check the tyre pressure when the tyre is cold. Then take a ride on your favourite twisty piece of road. Then, measure the tyre pressure immediately after stopping. If the pressure has risen less than 10% on the
front or 20% on the rear, the rider should remove air from the tyre. So for example, starting at a front tyre pressure of 32.5 psi should bring you up to 36 psi hot. Once you obtain this pressure increase for a given rider, bike, tyre, road and road temperature combination, check the tyre pressure again while cold and record it for future reference.

Each manufacturer is different. Each tyre model is different. A tyre design that runs cooler needs to run a lower pressure (2-3 psi front) to get up to optimum temperature. The rear tyre runs hotter than the front tyre, road and track. So the rear tyre cold-to-hot increase is greater. Dropping air pressure has the additional side effect of scrubbing more rubber area.

For the track you'll have to drop the cold tyre pressures an additional 10/20%. Track operation will get tyres hotter (increasing the cold-to-hot pressure range) so starting at say 32/30 psi now should bring you up to the same temperature (and pressure) that 35/39 psi gave you for the street.

Don't even think about running these low track cold pressures on the street.

Finally, dropping tyre pressures on street tyres for track use has its limitations, so street compound tyres on the track often get too hot and go beyond sticky to greasy. That's why you have race tyres. Race tyre compounds are designed for severe operation at these higher temperatures for a limited number of thermal cycles. On the other hand, race tyre on the street usually won't get up to the appropriate temperature for good performance. At street speeds, the race compound often won't perform as well as a street tyre.

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post #5 of 6 Old 06-06-2007, 7:23 AM
 
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Re: Tyre pressures

Darkstar - I run the same 42/36 stock pressures in the shitty UK unless on a track, again no slips and to the edge - beleive me it gets a thrashing Anyway, not so shitty today but had a puncture on the way to work £114 later I have new back tyre fitted.
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post #6 of 6 Old 06-06-2007, 7:24 AM
 
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Re: Tyre pressures

Is that what the book says then? I never looked it up lol
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