TimZ

Hey guys - I STFA but couldn't really find solid answers. I'm running 255/30/19's on my '02 S6 Avant. I've been keeping the tire pressure around 36. Is this about right?
Thanks
Tim

uberwgn

Tim, will you take a look in your owner's manual? It's probably similar to our '06 Avant, manual shows pressures for 16", 17" and 18" wheels. You should be able to extrapolate for the 19" setup. I start with something like 35/33 and see how that feels.

devinsixtyseven

Get a piece of white chalk, and do this on a flat paved area, with the tires cold, on an average day (ie not when it's 120 out, or 30 below).

Put a nice coating of chalk on a band across the tire, several inches long. Coat every tread block, side to side.

Now pull forward one rotation of your tires, and inspect the chalk mark. If it's rubbed off in the center but not the edges, remove a pound, rechalk, recheck. Missing chalk from the edges but not center requires the opposite treatment.

Once you've established an even contact patch, double-check and write down the pressure in each tire. Drive around for five or ten minutes, then recheck the hot pressure...it should be no more than 10% greater than the cold pressure. If it's beyond that threshold, add pressure, and yes I did mean to write "add".

Don't worry about minor variation side to side, but do note differences front to rear.

You can also call BFG and provide your original and new wheel & tire sizes, and they can ballpark a starting point for your tests.

I would NOT, under any circumstances, attempt to extrapolate pressure from the table posted above. It does not account for differences in sidewall or tread construction that will lead to more or less sidewall flex. Flex builds heat, heat is what creates and destroys tires. If the tire is over-inflated, you will prematurely wear out the tire by running on the center of the tread, and the vehicle will be less stable.

Underinflation is what causes accidents, as the tire no longer flexes at the shoulder as designed...it will flex at the sidewall, where the construction is thinner and less able to dissipate heat.

Don't assume, make sure it's correct for your tires and your vehicle. Don't even assume that the manufacturer's listed numbers are 100% correct, though I would put more faith in Audi's numbers than the numbers on my truck, which gave only the full-load spec. Audi provides far more information...it's good to see.

-Sean

jadatis

You can re-calculate it with spreadsheet I made.
In this I use the official system that since 2005 also in America is used and since <>1980 in Europe.
I once got hold of it and worded it out.
It can give different pressures , lower for maximum load , but that is because after 2005 Also in Europe they overreacted on the Ford/Firestone affaire.
http://cid-a526e0eee092e6dc.office.l...0tyre-pressure
In this map spreadsheets and examples to re-calculate for other then original tires. Download and open the spreadsheets in Excell or compattible programm to work with it, In the browser wont work becouse it cant handle protection and data-validation, I used in it. From this link you can navigate my complete public map of skydrive/hotmail for more, and if you cant work it out, ask me here

The tires on the picture of uberwgn are all XL tires that work with a reference pressure of 2,9 bar/42psi in Europe. From this they calculate the needed pressure with the formula , and this Ref.press must be highend up for higher speed with a sertain system. I all worked that in the speadsheet.