Basics of Tire Pressure By Annie Sam tires, pressure, performance, racing, set tire pressure, grip, road racing, drifting, psi

Basics of Tire Pressure
By Annie Sam

Tires. Such a small portion of the car, yet it is the most important part of your vehicle. Why? Because it is the only part of the car that comes in contact with the road – or at least the only thing that's supposed to come in contact with the road. So critical is having the proper tire pressure for performance and safety at speed, we'll devote this next article on how to correctly set pressure for your car for optimal handling and safety.

Now that you've been on the road course - having dutifully taken my advice, you should be a pretty kick-ass driver, maybe even able to take out the top Performance Touring drivers (hehe). The more experience you have on the road course, the more alert you will become in feeling out the kinks and quirks your car may have. Don't worry –you'll develop these senses gradually with the more track time you have.  Being aware of that fact, let's get down to the basics so you'll at lease know what to look for. - Basics o Tire Pressure

The Set Up

When driving on a racetrack you should run a higher tire pressure than you would normally run on the street. A higher pressure helps keep your tires from rolling over onto the sidewalls and destroying the outside corners of your tread under hard cornering.  A tire inflated to a higher pressure will also run cooler at high speeds, important to avoid chunking and tread separation. The baseline hot tire pressure for most cars is usually from 38 to 45 PSI.  Remember, running this pressure all the way around is a suggestion for FWD or 4WD cars.  A RWD front-engined car usually has a little more pressure in the front wheels. A rear or mid-engine car usually likes more pressure in the rear wheels. When your tires are cold in the first session in the morning, you have to remember that your tires will heat up, increasing the pressure in the tires.  Generally, the tire pressure at racing speed will increase about 1 PSI per 10 degrees of ambient temperature.  So if it's an 80 degree day and you'd like your tires to be at 38 PSI hot, set the tires at 30 PSI cold. Check and adjust your tire pressures immediately after your run group while they are hot.  This is very important for accurate adjustment. Now you will have your correct tire pressure for running.

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Wednesday, August 05, 2009 6:09 PM
i dunno if it is wrong or i dont get it right.
"Generally, the tire pressure at racing speed will increase about 1 PSI per 10 degrees of ambient temperature."

so 10 degrees starting from zero ˚, or 10˚ from the ambient temperature?

if the temp inside my tires is 30˚ and outside the temp is 80˚ the psi will increase for the 30˚ inside and the plus 50˚ outside giving a total of 8 psi?
or is it diference between the inside of the tire and the outside?

for example if my tires are at 50˚ and outside is 50˚ they will get hotter every time they gain 10˚ internally. at the end of a session my tires are at 60˚, then i can asume that the tires now have 1psi more than before?

using the same example from the last paragraph, how about tires going over the temp of the ambient? say there is a 50˚ day but your tires are at 60˚ or 70˚. you would have to take the temp at that time, when the tires are hot, or else you asume you are running a lower pressure than you really are.

i am not getting it. maybe is my english. maybe i am confusing myself.

when i do go to the track i always inflate a couple psi less than the max acknowledging (thanks spellcheck!!!) the expansion but i never took any temps.

good post. good read.
Tuesday, August 11, 2009 5:01 PM
= If you start off at 30psi "cold" (ambient temp), and if it is 80*F outside, then the general rule of thumb from that quote would be your "hot" pressures would be 38psi hot. 80*F = 8psi gain from base pressure, 30 + 8 = 38psi.

Depending on the weight of your car, the power, tire width, compound, etc... You don't want to be higher than 40-45psi hot. Setting your cold pressures just below max is far too high. Try starting at ~30psi cold and go from there.

Using the pyrometer, it is better to air with slightly higher inside temperatures than outside.
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