drrick89

Well, it is Discount Tire. What are you going to do?

But, back to tire pressure. With me a bachelor, I generally have a light load while driving - not that I'm a light-weight or anything like that... Regardless, 39 PSI for my front tires seems agreeable to most everyone. But, how about those rear tires? Why would I want 35 or 36 PSI in the rears instead of 39? In other words, how does having less air pressure in the rear tires - compared to the front tires - change the S4's driving dynamics, handling, ride, gas mileage, etc.?

rktskicar

I run 39f 36r on 18's

Bruce

drrick89

Understood Bruce, but why? Why not just run 39 PSI in the fronts *and* the rears? What does does running only 36 PSI in the rears do for the S4?

Zed 2.0

No controversy to be had. Your manual sets out the exact pressures you should run F/R at various loads and tire sizes. Fill to correct pressure and save the setting in MMI.

phil47

It's to improve the handling. Running slightly lower pressures on the rear reduces understeer as the front will have slightly improved grip for turn in while the rear will have slightly reduced grip and will rotate more.

drrick89

Thanks! This is the answer I was looking for. I assume this is because an A4/S4, though it has quattro, is still weighted like a FWD car; with a heavier front end. In contrast, a rear wheel drive car, like a BMW 3-series, is closer to 50-50 - with its rear while drive. So, you'd be more likely to put in the same air pressure in the front & rear tires in that car.

phil47

Yes. I also own a BMW E53 (X5) that stipulates slightly higher pressures in the rear for more balanced handling (they prefer to dial in a bit of understeer on this heavy SUV) when running the same wheel/tire size front and back. I do this for my winter package. However the OE summer sport package comes with a staggered tire setup that runs considerably wider rubber in the rear. This provides a similar effect w/o having to adjust pressure so they stipulate the same pressure front and rear.

westwest888

Just inflate it up to 41 or 42 all around so you don't have to worry about it as often.

Evlengr

You havent asked if it was cold or hot pressure? I would go cold 39 psi as a long trip or hot day will raise it to 41 anyway and a very cold day will drop it down to 37 psi.

weirded

I've experimented with this a little bit over the past few weeks. Started out with the OEM 19" summers on peeler wheels. Came from the dealer with 35 psi. Once I realized, I decided that was too low. Inflated to 41 psi. The right was pretty harsh. Right around that time, I switched to 18" OEM wheels with Dunlop 3D 225/45R18 winters. Wheels Works inflated them at 37 psi, which, again, I thought was low. Went to 41 psi, which was too harsh for the rough roads in the SF bay area. Lowered it to 39psi yesterday and drove 180 miles up to Lake Tahoe. Decided 39psi is the sweet spot for me.

I normally drive with 1-2 people in the car, rarely more.