Best Tyre Pressure for S3?

I just use factory settings.

To compare, My old 8L S3's on 18" used to be 36 psi all round.

Use factory settings - two reasons.............

1. Audi have spent £££££££££££££ getting the correct tyre pressures for the car.
2. Should you be involved in an accident the chances are the police will check the tyres and their pressures so if you do not have the correct pressures it could invalidate your insurance.

Also tyre pressures should be set with the tyres cold - donot trust forecourt machines, buy a quality pressure guage

I run mine 43 F and 38 R. I do carry read seat passengers at times so no point just leaving them at 33. If you do then the first time you have a rear seat passenger you have to inflate the tyres. I only do that cus the door sticker says so. Like above. Audi are recommending it so who ami to argue? Lol

I've played around and found that the factory settings or near as dammit were about the best.

Cast your eyes over these from the inside of my door. I run 42 front 40 rear.

Factory recommendations are for Audi to achieve their NEDC fuel economy mpg figures with least rolling resistance.

They aren't the same for other criteria, eg: maximum grip

I've played around with them too and factory is best!!

More tyre pressure recommendation threads:

http://www.audi-sport.net/vb/a3-s3-...ost-your-recommended-tyre-pressures-here.html

http://www.audi-sport.net/vb/a3-s3-sportback-8p-chassis/161806-tyre-pressure-thread.html

Guys mine says 33 PSI but when I inflate them seems too LOW!!! Any idea why!?! I check the tyres, everthing is same but looks too low, so i leave them on 40 PSI...

Anybody rekons anything...

Cheers

The physics of tyre pressure needs to be considered when we wonder about the recommended pressures for low profile tyres seeming too high (especially if like me, you're used to higher profile tyres at lower pressures previously)

Lower profile tyres have a smaller containing volume because the air cavity inside the tyre is smaller but the quantity of air in the tyre is not too far off what you would get in a higher profile tyre - the main difference is volume. Let's look at an example...


The Ideal Gas Law, of course, defines the relationship between volume, pressure and temperature so it's no surprise that smaller volumes at higher pressures (at the same temperature) require proportionally equivalent quantities (i.e. moles) of gas as larger volumes at lower pressures.

Simply put, one should expect to see higher pressure requirements for lower profile tyres because of the reduced internal volume of the air cavity (plus some variation for the model and performance characteristics of the car, I expect). Hell, road bicycle tyres can be ~80 psi + for the same reason: relatively small internal volume to hold the quantity (moles) of air required to retain tyre structure.

Now, comparisons with tyres and balloons or tennis balls are flawed because tyres are constructed very differently and this is important for considering under-inflation for comfort or grip reasons. Slight under-inflation is probably ok but go too low and the shape of the tyre distorts as per this well known image...


The construction of tyres cause concave deformation if they are under load but soft on pressure. Go too soft and you end up with less contact patch and less grip, not more, with increased wear at the edges.

So, I would probably not deviate more than a few (<5) psi below the factory recommended pressures personally. Experiment and observe wear patterns (I wonder if there's a way to do a short term tyre wear test using a safe paint? This paper seems to suggest it is possible).

I probably should double check the figures above but I'm off to watch the Malaysian F1