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RS4's cold tire pressure


MIata Tom
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4 hours ago, Richard said:

We aim for 32-34 hot on both the 225 and 245 (15x9) with our 2200lb Civic.

 

Contrary to what Rob (wvumtnbkr) posted above; we find it easier to let air out on every pit stop, not just the first one!

 

Yep.  This is exactly what we do.

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Our testing with a pyrometer had us less than 20psi cold with a 24psi hot target, but also less than 2 degrees of camber with the 245.  These findings are counter to what alot of people think and run, but we used data to get there and I think it's arguably the fastest car in ChampCar on the brakes and in the corners.

 

https://ruggedbadger.com/the-car-build/

 

 

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4 hours ago, LuckyKid said:

Our testing with a pyrometer had us less than 20psi cold with a 24psi hot target, but also less than 2 degrees of camber with the 245.  These findings are counter to what alot of people think and run, but we used data to get there and I think it's arguably the fastest car in ChampCar on the brakes and in the corners.

 

https://ruggedbadger.com/the-car-build/

 

 

Damn!  Your car must be light!

 

We did a test day with several different brands of tires and used a pyrometer as well.  With a 2400# rwd rx7, the rs4 were happiest at 34 hot.  I hope on this next build I can cut 200# out of the car, and go to a wider tire.

 

Your tire wear is probably amazing!

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42 minutes ago, wvumtnbkr said:

Damn!  Your car must be light!

 

We did a test day with several different brands of tires and used a pyrometer as well.  With a 2400# rwd rx7, the rs4 were happiest at 34 hot.  I hope on this next build I can cut 200# out of the car, and go to a wider tire.

 

Your tire wear is probably amazing!

We are at 1975 wet.  We haven't worn through tires yet, but we've curbed and flat spotted a few.  We expect a new set will last the 24 at VIR.  

 

In my "career" I've never ran as low of pressures as we are now, but it seems to be working well with our miata.

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Does anyone run nitrogen in your  tires?  I have not done it in Champcar yet but, every other form of racing that is what everyone ran.  We have found the the RS4's will wear alot better up to 40 psi.  We shoot for 38 hot.  That put us around 30-32 cold depending on ambient temps.

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Curious to know how the tires wore at Indy?  I've been running 225 RS4s up until Indy, for this race I tried RE71R (got at a discount), ended up using a full set each day.  I had a lot of outside wear on the tire, running basically 0 toe F/R and -3/-2.4 camber.

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We ran 32 hot on Saturday and car had  a lot of push to it that we hadn't had before. Car was better on Sunday running at 34 hot. Had good tire wear even with the 3/16" toe out we developed on Sunday due to contact.

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1 hour ago, wvumtnbkr said:

Indy was tough on tires from what I saw.

 

I know both front running teams had to change tires on sunday during the race.  1 car on rs4.  The other on re71r.

Indy was a bit easier on tires than NCM last year in similar temp conditions. Worse than Road America, but RA has much cooler temps so I don’t know how much you can draw from that comparison.

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  • 2 weeks later...

The stuff the big boys put in their tires only grows about 2-3 psi. So it’s not ALL about moisture. It’s expensive and is only an advantage for a lap or two after restarts and pit stops. Could be worth a couple seconds at most in an endurance race. The question is whether temps or pressure is more important on a short run like qualifying.or restart with a 1-2 lap advantage. Testing for Qualifying has shown me that not compensating for the short run with a pressure increase, reduced grip and slowed lap time.So that build up time matters to some degree. But is it worth it money wise? If we always had nose to tail finishes I would say possibly. But to keep it affordable I say no. Unless it’s Indy or Daytona...

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