195/50/15... Recommendations for air pressure front and rear?

[steiner_ca at hotmail.com (Craig Steiner)]

For the budding engineers on the list, I've found the "High-Performance 
Handling Handbook" by Don Alexander and "Tune To Win" by Carroll Smith to 
have some of the best tire tuning procedures/info.  That is, they have 
excellent descriptions and numbers to tune by.  I've yet to apply this 
knowledge as my 16V is still just a DD, but the plans are in work and the 
money has just arrived.

Don Alexander's book describes how to use a tire pyrometer and a set pattern 
of taking a tire's temperature to determine proper inflation/chassis tuning. 
  For example: Tire temps (inside, middle and outside) of 195 180 190 would 
indicate that tire pressure was too low.  185 190 180 would indicate too 
high a pressure.  195 190 185 would indicate correct pressure.  Essentially, 
you'll want the inside temps 5 to 10 degrees hotter than the outside with a 
middle temp somewhere in between.  It should be noted that correct temps 
alone don't necessarily mean your pressures are correct.  Tire temps will 
also indicate a number of other problems such as incorrect camber, toe, roll 
steer, rear axle steer etc etc. There's much more detail in the book.  Yeah, 
there's a Honduh on the cover, but there are several VW examples in the 
book, including a Corrado, NB Cup cars, several Audi examples and 6 pages 
dedicated to tuning VW's (1983 GTi and a 2000 Neuspeed Golf 1.8t).   BTW, 
Carroll Smith's book isn't written for those who flunked out of Physics and 
Math in high school.

Craig Steiner
'88 Alpine White 16V - stock

Emerging once again from lurk mode to get this project rolling!

>From: "Allyn" <amalventano1@tds.net>
>To: "T Berk" <tberk@sbcglobal.net>
>CC: scirocco-l@scirocco.org
>Subject: Re: 195/50/15...  Recommendations for air pressure front and rear?
>Date: Wed, 15 Dec 2004 17:59:12 -0500
>
>>(Three of the four on Tire Rack are rated @ 44 psi Max, the fourth is 
>>rated @ 51 psi Max.)
>>
>>I'm thinking Higher is Better.
>>
>>TBerk
>
>i totally agree here. the few times i've autocrossed the rieger (kumho 
>712), i've noticed that lowering tire pressure only seems to give an 
>advantage in slow speed tight cornering. i believe this is due to the 
>uneven contact patch that results in stock caster, low roll rate, and high 
>steering angle (outside front tire - inner part of tread has greater 
>contact than outer).
>
>in all other situations (higher speed cornering), the advantage is had when 
>the front tire pressure is closer to the rated sidewall marking. the higher 
>pressure causes far less give in the sidewall area, which also helps reduce 
>the slip angle of the tire (due to less tread section compliance around the 
>contact patch area).
>
>i came to these conclusions when i did the g-tech pro runs on the rieger. i 
>spent an afternoon experimenting with different tire pressures / speeds. i 
>found that tight/slow cornering was best at ~30 psi, while higher speed 
>cornering was best at the sidewall rating (44 psi). also, pressure had a 
>greater impact on the slow than the fast (so if you were trying to dial in 
>for both situations on the same course, it would probably be better to be 
>on the low side). for example, i generally run the rieger at 30-32 at the 
>autocross (i bump the rear up to 45-50 to help get some more lift throttle 
>oversteer in tight cornering). any other time (daily driving) i run 45 
>front / 40 rear.
>
>other pros/cons of higher tire pressure:
>pro: less risk of wheel damage on rough roads / less rolling resistance -> 
>better mileage
>con: slightly less ride comfort / greater chance of wheel hop on a worn out 
>suspension
>
>note: this info was gathered with treaded street tires that had nearly full 
>tread. other tires (lower tread, autox prepped tires, slicks) will have 
>different charactersitics and work best with different pressures.
>
>hth
>Al
>
>
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