dpcompt

I just replaced the tires on my wife's 2020 S5 SB from 265/30 to 275/30 tires (Stock 20x9 wheels). Should I be lowering the tire pressures a small amount? I noticed that the recommendation for the 275s is lower fro the RS5 cars.

Zombie5150

What were you running the 265’s at?

dpcompt

42f, 38r

Zombie5150

OK. My car came with 275’s (20x9). I changed to 285’s (20x10) but pretty much ran the same pressures. I tried several different combos but my preference remains at 39f/36r. I don’t haul a lot of people. Most of the time just me. Occasionally the wife.

PWDRSKR

I suggest you check outTire Pressure Calculator to calculate the proper pressure for your wider tires. I also run 285/30/20s and found that the wider tire requires a lower pressure compared with the OEM tires. Delta is generally between 1-3 PSI below the OEM values.

Also recommend using the tire pressure table located in the manual over the door sticker. The pressures on the door sticker are for a max loaded car. If you’re like us, we never have more than two people in the car, a far cry from a max load. In our case, the recommended tire pressure for non-max load is 36/33 PSI (Front/Rear). Because I have wider than OEM tires, I tracked down a resource, Tire Pressure Calculator, to figure out what pressures to use. The result: 34/31 PSI (Front/Rear) with a normal load. Car drives great.

Zombie5150

OK thanks, I’ll check it out.

Glisse

I agree with your well made comments.

However, the differences in pressures are not due to 10mm of extra width, but due to the load ratings of the respectives tyres. The 265/30R20 OEM tyre only had a 94 load index, which is low for the S5. As a consequence, it requires higher pressures to offset the softer sidewalls. The 275/30R20 OEM tyre for the RS5 has a load index of 97, which is about right for the S5/RS5. Which is why the OP noted the lower pressures for the RS5's 275 tyre.

In your case, you will find the Tire Pressure Calculator has given you a reduced pressure for your new 285mm vs old 275mm tyres because the calculator has assumed your new tyres now have a higher load index - 99. Which is too high for an RS5, but using lower pressures can mitigate any harshness from the stiffer sidewalls.

Unfortunately load index is something that is often overlooked, but it plays a key role.

dpcompt

Thank you for your reply. When looking at the Audi Handbook's recommended pressures I originally noticed that the 275/30 tire on the RS5 had significantly lower pressure recomemdations than the 265/30 size for the S5. Your statements make a lot of sense. This is the info I was looking for.