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Old 05-27-2008, 02:57 PM   #10 (permalink)
EcoModding Newbie
Join Date: Apr 2008
Location: Southern Ontario
Posts: 284

Parachute - '03 Chevrolet Tracker LX
90 day: 28.55 mpg (US)

Peon - '95 Plymouth Neon Highline baby!
90 day: 31.39 mpg (US)

Slocus Wagon - '06 Ford Focus SE
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Capriracer can confirm this for sure, but I believe the sidewall max psi is for when the tire is cold. The pressure will go up while driving fast but I'd assume that has been considered when the engineers set the max psi rating.
ie, no problems doing 75mph in death valley in the summer at max rated load...

I've been doing some autocross lately with my 95 Neon, and with all season tires, P185/65R14 which are relatively narrow high profile tire common on most cars, I get the best times at about 46psi cold in the front tires, and 35psi cold in the back. Autocross is basically 80 seconds of extreme accident avoidence manuevers at relatively low speeds, up to 40mph in our area. So I would say that running higher psi is definitely safer for city driving. You turn the steering wheel and your car turns quicker and more predictably, there is less deflection from the wheel rim to the contact patch on the tire.

As for absolute braking performance in a straight line, I bet 10psi is best for the rear tires and maybe 25 psi in the fronts. That would give you 4 big fat contact patches. Not good for anything else like turning or going through potholes though....

No tire or tire pressure is close to optimal for all conditions. By inflating your tires up to or slightly beyond the max on the sidewall you might be increasing your stopping distance by 2% on clean dry pavement, you might be reducing your risk of aquaplaning by 2% and you are able to turn 4% better while saving 4% more fuel... Or not, unless you have team of engineers test your tires on your car on your roads you'll never know for sure.

For me, I'm comfortable running 40psi in all tires on both my Neon and Tracker, this is 5psi over the sidewall max for the Neon and the Tracker. I don't drive 100mph for hours in the desert and I can see that tire is very much in contact all the way across the tread so I think this is good comprimise. YMMV.

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