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Old 01-19-2013, 11:53 AM   #1
Uruchima
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Member#: 322246
Join Date: Jun 2012
Chapter/Region: South East
Location: Boca Raton, FL
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2013 WRX Sedan
Black

At the Track Tire Setup for Homestead

Whats up Nasiocers... going to Homestead tomorrow for the first AutoX of the year... Done quite a few of these and just wanted some input on Tire Pressure...

I'm running a '09 Subaru Impreza 2.5i. Cosmo CAI and OBX Catback with a Open Source Tune. Eibach Sport Springs, Rear Perrin Sway bar and Hankook V12 EVOs 205/55/16 Car weighs 2900 with me in it... what do you think would be the best tire pressure? and how do I normally figure this out in the future?

76F and 66% humidity in Homestead tomorrow.
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Old 01-19-2013, 04:02 PM   #2
leecea
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Those tires may not be that great for autox but you'll still have fun. Here is what I'd do, but it's not at all scientific, so see if you get any better answers

You'll need a reliable gauge, some chalk, and a source of air.

At the start of the event, pick a relatively high target tire pressure for each end of the car, something like 45 psi F, 43 psi R and set them to that pressure. Now draw chalk lines from the tread to the sidewall of each tire at roughly 12, 3, 6, & 9 o'clock positions.

Take your first run.

Look at the wear of the chalk lines. The idea is to get the chalk worn off the tread, right up to where it joins the sidewall, but for the chalk to remain untouched on the sidewall itself. This means you are using all the tire's tread but not rolling over so much that you're scrubbing the sidewall on the track.

If you have worn chalk off the sidewalls at the front or back, add a couple of psi to the target tire pressure for that end of the car. If the sidewalls still have chalk, subtract a couple of psi for the tires at that end. Now you have a new target for each end, so reset your pressures to that target before the next run.

Before each run, draw the chalk on again. After each run, check the lines, adjust your target pressure for each end, and adjust the pressures before the next run.

After a few runs, you'll probably have zoned in on the minimum pressure that keeps the sidewalls safe. Now all you have to do is check the pressures after each run because heat can cause them to increase.

This should get you started and give you pressures you can run at each event. I'm sure it won't get you the "best" pressures but you may need an onsite expert to drive the car for that anyway.
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Old 01-19-2013, 04:19 PM   #3
Uruchima
Scooby Newbie
 
Member#: 322246
Join Date: Jun 2012
Chapter/Region: South East
Location: Boca Raton, FL
Vehicle:
2013 WRX Sedan
Black

Default

Quote:
Originally Posted by leecea View Post
Those tires may not be that great for autox but you'll still have fun. Here is what I'd do, but it's not at all scientific, so see if you get any better answers

You'll need a reliable gauge, some chalk, and a source of air.

At the start of the event, pick a relatively high target tire pressure for each end of the car, something like 45 psi F, 43 psi R and set them to that pressure. Now draw chalk lines from the tread to the sidewall of each tire at roughly 12, 3, 6, & 9 o'clock positions.

Take your first run.

Look at the wear of the chalk lines. The idea is to get the chalk worn off the tread, right up to where it joins the sidewall, but for the chalk to remain untouched on the sidewall itself. This means you are using all the tire's tread but not rolling over so much that you're scrubbing the sidewall on the track.

If you have worn chalk off the sidewalls at the front or back, add a couple of psi to the target tire pressure for that end of the car. If the sidewalls still have chalk, subtract a couple of psi for the tires at that end. Now you have a new target for each end, so reset your pressures to that target before the next run.

Before each run, draw the chalk on again. After each run, check the lines, adjust your target pressure for each end, and adjust the pressures before the next run.

After a few runs, you'll probably have zoned in on the minimum pressure that keeps the sidewalls safe. Now all you have to do is check the pressures after each run because heat can cause them to increase.

This should get you started and give you pressures you can run at each event. I'm sure it won't get you the "best" pressures but you may need an onsite expert to drive the car for that anyway.
Thanks so much, I've heard a lot of the chalk process but nobody explained it. Thanks brother.
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