BarryT

I have a 2014 TDI with the 20" wheels. The door sticker says to inflate the tires to 33psi max. The owners manual states the same for a W rated tire, but directly below the Q5 values the SQ5 values show a higher psi for the same size tire with the same rating. What's the difference? They have the same size tire with the same W rating. Mine are 255/45/20 105Y. Should I use the higher psi (39psi) or the 33psi that the label shows on the door? The tires look a little low with the 33psi in them.

riceboy22

My recollection from some other threads on this topic was that it's a mix of ultimate top speed and legal requirements. After toying around with pressures, I run my 255/45/20s on my SQ5 at 36psi front-and-back.

awryexperiment

Barry, what is the max pressure stated on the sidewall of your tires? I wouldn't go above that pressure.

uberwgn

Barry, in the USA, the door sticker displays MAX LOAD only. You've got to refer to your Owner's Manual (for your vehicle) for comprehensive inflation pressures for a normal load unless the vehicle is being operated as a taxi cab, etc.

ex-quattro PETE

Is the load rating the same on both tires?

As I mentioned in the other thread, I suppose they expect an SQ5 to be driven in a more spirited manner, in which higher PSI might provide crisper response and also reduce heat.


Looks can be deceiving. Most low profile tires will look kind of flattened, even if they are inflated correctly.

I'd start with 33 PSI and see how you like the ride. Then go up a few PSI from there and see if you like it any better. You'll be trading ride comfort for steering response, and only you decide which one you like better.

Redd

I believe the "W" rating is a maximum speed rating. As tires run faster (or are smaller diameter) they will run hotter at the same vehicle road speed. So a smaller tire, or one simply running at higher speeds, will heat up more and the air pressure in it will increase higher over the "cold" inflation pressure.

The bottom line is always follow what is stamped on the tire, that is specific to the manufacturing and use of that tire. The owner's manual and door sticker are making general presumptions about what will be on the car, usually based on size alone, and probably will be more conservative.

A call to the tire maker should confirm this. (Or refute it.(G)

ex-quattro PETE

What's stamped on the tire is the max cold inflation pressure. It has nothing to do with what you should actually run it at, other than you should never exceed that number. The tire manufacturer has no idea what vehicle you are going to mount that tire on.

Redd

Ergh?
But aren't you supposed to be inflating them COLD?
And then, regardless of what hairbrained kludge someone has come up with ("Dude! I just know I can fit 13" tires on this lowrider!") given a particular tire size and a particular speed rating, they do know how fast and hot it is going to run, once it runs. Sure, you can exceed weight ratings, but if you are using the tires spec'd by the carmaker, they have already taken that into account with the gross vehicle weight and the payload that are also designated for the car.

A friend of mine had an Accord. And decided, he could certainly fit more bags of landscaping stone in the trunk. Can't blame Honda if that broke the shock absorber, he tried to load a thousand pounds in a seven hundred pound bag. (So to speak.)

Now, if Audi was really a high-technology car company, they would mount a non-contact IR thermal sensor in each wheel well, and monitor the tire temperature. Any discrepancies between the four, factoring in sunlight, would indicate another problem to be attended to. Possibly from carrying a Sumo team on underinflated tires.(G)

ex-quattro PETE

Yes. Did I say something different?
All I said is follow the car mfg PSI recommendation and not what's stamped on the tire.

Exactly. And that is why you should follow the PSI specified by the car maker, too.

The same tire can fit on a multitude of vehicles, and each will have a different PSI recommendation based on the vehicle weight, suspension tuning, and probably a number of other factors that only the car mfg has tested.

That's a misuse of both the vehicle and the tire. You are on your own in this case. Nobody is suggesting the OP do this.


Right, more electronic gizmos to fail. That's exactly what we need.