Contour Enthusiasts Group Archives Forums General Autocross and Open Track What tire pressure are you all running at?

Andy that is the funniest thing I have ever heard on the board. AAAAAHHHHHHAAAAA!!!!!! Funny thing is it makes sense. I think it may only shave off a few lbs and not enough to make a difference. Plus helium could change the rate of tire expansion upon warm up. What a simple idea it was though really. I cant remenber where but an 18 wheeler got caught under a bridge and engineers were trying for hours to get it out of there. While in the traffic jam a little girl told her daddy "why dont they let the air out of the tires?" Daddy told the engineers and it was the fix. Amazing how simple ides can turn out to be the best ones. God bless the US for allowing us all to have creative minds of our own! BOS SVT

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2000 SVT green
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> Anyone ever thought about using helium
> in there tires to make the car lighter?

It was tried years ago and they found that helium leaked through the tire at a really fast rate. I seem to remember something like 10 to 20 psi per hour.

Most professional racers use Nitrogen to reduce thermal expansion.



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John Coffey
johncof@veriomail.com

True , helium finds ways to leak like no other gas (it's the smallest moloecule around). Thats why we leak check O2 systems with it. Nitrogen on the other hand has one of the lowest rates of expansion when heated or cooled. It's also cheap and inflammable. I know a few guys have put it in their tires to keep them from going flat when it hits -35 here in Canada.

Thanks all for all of the great input. BOS SVT

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2000 SVT green
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# 852 of 2150

On the subject of thermal expansion... I just read Carroll Smith's book "Drive To Win" and he states that thermal expamsion is mainly due to the amount of moisture in the gas that is used. Be it air or nitrogen. He says that nitrogen does expand less but that it also needs to filtered for moisture very carefully.

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Chris
2000 SVT

I have been racing a '95 Contour SE for the last 3 years and I normally run with 45 psi. in the front and any where from 37 to 32 psi in the rear tires. For me running at least a 10 lb. difference in air pressure between the front and rear tires helps to reduce some of the underster and with the use of some trail-breaking going into the corners the car will rotate more easily on entry to the corners. I have managed to win 3 Detroit region SCCA events and have way to many 2nd and 3rd places using these tire pressures. I have also been using Yokohama 509 tires in the standard 205/60-15 size but I am switching to Bridgestone Potenza RE730's. Both tires are a huge improvement over the stock tires but they are for summer only. If you want to go fast in autox competition spend your money on a good set of rubber and on a driving school because this is where you gain the most speed. And it's always fun to watch the Integra-R, Eagle Talon TSI, Audi TT & Probe GT people looking your car over trying to figure out why this 4-door family car is beating em'.

Finally ran some time-only runs yesterday at the CalClub autox at Anahiem Stadium. After 6 runs I settled on 44 front and 30 rear. The car felt balanced in the medium (40 mph +) to high speed autox corners but still pushed a lot int he low speed turns. I think I was just coming into them too fast. Three years of racing a Street Prepared 240Z gives you bad habits for front-wheel drive.

Another black SVT was there (exactly 12 days new) and the owner was experimenting with pressures from 55 to 50 front and from 15 to 20 rear. He ran .8 faster than me but he's been renting and racing Contours of various types for a couple years.

I think I'll go down another 5 on the rear if I run the car again.

BTW... 2000 Contour SVT on the stock BFG gforce KDWs.

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John Coffey
johncof@veriomail.com

[This message has been edited by johnc (edited September 25, 2000).]

Last week I tried going the other way on the rears. I tried 52f/48r, 52f/50r, 52/52 and 50f/52r. The car was definetly alot more free in the rear. I settled on 52f/50r. Seemed to be the best combination I've had so far.

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Chris
2000 SVT

Going to higher pressures in the rear is what I wanted to do last Sunday, unfortunately my air tank didn't have enough left after setting up the Z earlier in the day. Next event I think I'll start at the pressures you list above for the rear.

Years ago I autocrossed an Infinity G20 in ES and ran 38 front and 60 rear with good results. On bumpy courses I would have to reduce the rear pressures to stop some hopping that would occur.

Ultimately, when I can dial-in about 3/8" toe-out in front I'll be able to reduce the rear pressures to something a little more reasonable. BTW... is rear toe adjustable on the Contour? If so, whoopie!



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John Coffey
johncof@veriomail.com

John, I'm wanting to try some toe-out too. Haven't played with the alignment yet at all.

A little more info on the pressures I listed before. I thought the car turned in under brakes alot better. Kinda loose but not in a bad way. Just free. Corner exit under power was a little better but still had a push. The car needs shocks! Like always if you're not gentle with the brakes it will push bad.

I think it was in Sport Compact Car, they did an article on a CRX and they disconnected the front sway bar to keep it from picking up the inside front on corner exit. I've had this problem big time and had been throwing the idea around before I read the article. Don't know if I really got the nerve to try it though. Any thoughts?



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Chris
2000 SVT