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Old 06-28-2004, 12:50 PM   #1
TedMeyer
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Join Date: Mar 2004
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Location: Arizona
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Silver. Now w/ 100% 18G!

Question track pressure?

What's the procedure for determining the proper pressure for tires on the track w/o a pyrometer? I ran my first track day at Lime Rock last Thurs and really didn't have a clue. I ended up starting with the "mid-forties" after talking to one of the instructors, and took some air out after the second session to calm my oversteering rear.

I'm looking for any pointers, and/or specific suggestions for a starting point with the 225 17" Bridgestone SO3's. Didn't see anything with a search.



Ted
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Old 06-28-2004, 05:06 PM   #2
mav1c
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I run Toyo RA-1's and start with them around 34lbs cold. When I come in and check they're usually around 40-42lbs, depending on the air temp and how quickly I get stopped and can check. I figure I lose at least a pound of air during the cool down lap, so they're running around 41-43 hot which is about ideal for an RA-1. I'd say starting in the 40's is WAY too high. You build up a lot of heat at the track which is usually good for 7-8lbs of pressure. At least that's been my experience.
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Old 06-28-2004, 06:53 PM   #3
TedMeyer
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Thanks. Mine did jump by about 4-7psi hot which put me at the max psi for the 'stones. That's when I adjusted back down to ~46-43, and then later a couple psi lower at each end when I was still looking for some more grip. I did chalk the edges of the tires, and dropping the pressure didn't make a ton of difference in terms of how much of the shoulders showed wear. I didn't get enough sessions to experiment any more.

Anyone know an good target for hot temp psi for the S03's?

Ted
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Old 06-28-2004, 09:10 PM   #4
AJ711
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I would say to err on the high side.

I did the opposite down at Roebling Road Raceway outside of Savannah, GA and I nuked my tires. By the 6th twenty minute session in the afternoon, I had cord showing in small areas due to blistering.

So, now I need to buy a new set of BFGoodrich g-force KD's before the next track day event, but I learned a good lesson on proper tire inflation (and a refresher on thermodynamics).

Higher tire pressures mean more air is in the tire. And a greater volume of air heats up slower than smaller volumes (example; what boil first? a cup of water, or 5 cups of water?).

I was running with my auto-x pressures (35 psi all around), had great oversteer under full throttle and a well balanced car. However, I failed to notice (as did my instructor, no biggie) that my tires were getting too hot for things. When Jon K noticed cord showing at the start of my 6th session, I put more air in the one tire, went back out on the track and continued to shred the tires. I called it quits for the day on track tires, let them cool down, installed the daily drivers and went out one last time before being signed off to go solo.

It is going to be a test and tune game to find pressures that will keep the tires in optimal temps without ruining their performance and without causing too much wear.

Hopefully someone with the same tires has some input, though it will be something completely specific to the track you're running and the conditions present. However, having a starting point would definitely help.

AJ
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Old 06-29-2004, 02:45 PM   #5
wrxman02
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i run my re070 on the track at stock pressure. no issues at all.
i love them
later
andy
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