Tire Pressure?

[PeTTey]

I have the 18" RS4 type rims with Pirelli PZero's and I was wondering what the REAL correct tire pressure should be?

Under the gas cap cover, it says to inflate (with normal loads) the rears to 30psi and the fronts to 36psi.
When I brought my car to the dealer for the 30K service, I checked the pressure and: rears were at 42psi and fronts were about the same????
Sidewall of the tire has a note not to inflate past 50psi.

I deflated the tires back to the lower specs and it did feels little mushy in comparison but that seemed like WAYYY too much of a difference! I was told when I got the car to be VERY careful with the pressure since these tires depended heavily on the correct setting!
So what gives...is the dealer trying to kill me or are the settings indicated under the filler cap not correct for my tire??

[gonzo]

Well. Here is the deal with tire pressure settings.

Raise the front if you want to increase steering response. But don't go too high or you will hydroplain on water when it rains.

Raise the back if you want to dial out some understeer. Again do about 2 or 3 psi at a time till you've achieved the result you are looking for, not going over board.


As for setting it to 42, personally I think that's too high. On my TT is used to run 34psi in front and 37-39psi in back.

Hope that answers some of your questions.

[PeTTey]

Originally posted by gonzo
Well. Here is the deal with tire pressure settings.
<snip>
As for setting it to 42, personally I think that's too high. On my TT is used to run 34psi in front and 37-39psi in back.

Hope that answers some of your questions.

Thanks!!!

The only question I have is why Audi has the rears at about 6psi lower than the fronts and you are running slightly higher in the rears? Is there really no definitive answer? It seems that this is more like personal preference than anything!

Thanks again.

[Hutash]

42psi seems way too high. Where you measuring cold pressure both times? It make a big difference.
I have heard some mant different opinions on tire pressures that my head spins when every the topic comes up. I run mine at the factory settings, as recommended by the guys at tire rack. There have been many discussions in the tire/wheel forum, and that is the standard response. On the track I will vary my pressures to tune the car to conditions, up on colder days down on hotter days, but I still am not sure what is ideal. AutoXers use white shoe polish on the sidewalls to see if the tires are rolloing over alittle, and adjust as necessary.

[Ben@SpeedBarn]

I think the consensus with 18s has been between 38 and 40 psi. Lower pressure with 16s or 17s. Low 30s would really increase the chance of you bending an 18 inch wheel.

[PeTTey]

Ay Caramba...my head is actually starting to spin...maybe I'll put all four at 36psi and call it a day???

[Hutash]

To make it spin alittle more: you can run a higher pressure for better gas milage, and softer for a better ride. Being a front heavy car with front wheel drive (even quattro is still front wheel predominate) you should run the fronts about 4 psi higher than the rear.

[gonzo]

Originally posted by Hutash
To make it spin alittle more: you can run a higher pressure for better gas milage, and softer for a better ride. Being a front heavy car with front wheel drive (even quattro is still front wheel predominate) you should run the fronts about 4 psi higher than the rear.

Quatro being predominately front wheel drive , this is only true for the AUDI's/VW's featuring the haldex system. Not true for those that feature the Torsen system.

The primary reason for the tire pressure being higher in the front is:

A) the motor is up front
B) to induce understeer when the car is pushed to its limits

Remember, understeer is a lot easier to deal with than oversteer.

[Hutash]

Originally posted by gonzo
Quatro being predominately front wheel drive , this is only true for the AUDI's/VW's featuring the haldex system. Not true for those that feature the Torsen system.

The primary reason for the tire pressure being higher in the front is:

A) the motor is up front
B) to induce understeer when the car is pushed to its limits

Remember, understeer is a lot easier to deal with than oversteer.

That is the point I was trying to make, the TT has Haldex, and therefore front wheel drive predominates, which increases understeer. The higher pressure helps to correct it, plus the front is about 10% heavier than the rear.

[Ben@SpeedBarn]

Actually to get rid of understeer you would need to have a higher pressure in the rear. Like gonzo said higher pressure in the front will give you more oversteer.