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Old 16-Jan-2005, 08:17 PM
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winter riding tyre pressure

does anybody have any veiws about changing pressures for winter riding.
i know when doing track days its advisable to change them as the tyres warm up a lot quicker/higher
so as the tyres dont really get warm this time of year does anybody change there pressures and to what
i run at 30 front 32 rear
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Old 16-Jan-2005, 10:28 PM
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Someone told me that if you run lower pressures in winter then the grooves in the tyre close up and if its wet the tyre cant displace water properly.
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Old 17-Jan-2005, 02:33 AM
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The gods must ride Ducatis because they created the Ideal Gas Law, that automatically lowers the pressure in your tires when the temperatures drop in the winter.
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Old 17-Jan-2005, 03:00 AM
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good thread.... please help me too, i have pirelli diablo's front and rear on a 748E and run at 34F 38R at all times...but some have said to put more in (40 in rear to boost shape) and less too - yes i can feel the difference but can't decide what is right - any help?
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Old 17-Jan-2005, 01:58 PM
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I run 32F and 35R all the time, except on track when it is 30F 30R.

I'd be interested to know what's the best plan.
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Old 17-Jan-2005, 05:47 PM
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You'll get a lot of opinions on what tire pressure to run, but the correct tire pressure for you is not a matter of polling other rider's opinion. Here are the basics you'll need to decide for yourself.

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 tire wear. Further, if you're running alloy wheels on poor pavement, consider adding 2 psi to the recommended tire 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 tire pressure regularly as they say.

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

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

First check the tire pressure when the tire is cold. Then take a ride on your favorite twisty piece of road. Then, measure the tire 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 tire. So for example, starting at a front tire pressure of 32.5 psi should bring you up to 36 psi hot. Once you obtain this pressure increase for a given rider, bike, tire, road and road temperature combination, check the tire pressure again while cold and record it for future reference.

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

When I used the tire pressures recommended by Ducati (32.5F/36R) for my 916 on my favorite road, I got exactly 10/20% on a set of Bridgestone BT-012SS. So I guess I'm an average rider and the BT-012SS runs at an average operating temperature compared to other brands.

For the track you'll have to drop the cold tire pressures an additional 10/20%. Track operation will get tires 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 tire pressures on street tires for track use has its limitations, so street compound tires on the track often get too hot and go beyond sticky to greasy. That's why you have race tires. Race tire compounds are designed for severe operation at these higher temperatures for a limited number of thermal cycles. On the other hand, a race tire 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 tire.
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Old 17-Jan-2005, 06:32 PM
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good reply
is there any thing that shazaam doesn't know?
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Old 17-Jan-2005, 07:45 PM
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Wow, great detail there Shazaam. I checked mine before my little 70 mile bimble yesterday and put them up to 35R and 32F. Felt I was getting reasonably good grip in spite of the slippery roads but didn't feel confident enough to really rely on it. But that's just my more cautious riding in winter.

Next time out, I'll give the 'warm and re-presssure test' theory a go and avoid the guesswork. Thanks for taking the trouble.
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Old 18-Jan-2005, 02:22 AM
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Very interesting, Shazaam. Here's a question: Supposing you have access to a pyrometer or surface thermocouple doodah, what temperature should the tyre surface be at once it's warm?
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Old 18-Jan-2005, 06:57 AM
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The rubber stickiness, and therefore the tire grip, increases with the temperature until some optimum value is reached - different for each tire formulation, but usually around 95C for street tires. Above its optimum temperature, the tire rubber gets too slippery.

Heres some temperature readings taken with an infrared non-contact temperature sensor. Its easy to see it was from a clockwise race course.

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