Thoughts On Tyre Pressures

[RustyBucket]

I posted this as part of a conversation in another thread but I'm interested in others thoughts on this:

I had an interesting chat with my mechanic on Friday about tyre pressures. I was having the 4 wheel alignment done on my 2006 S3 on 225x40x18 and had set all the tyre pressures before hand, 39 front and 30 rear as stated on the inside of the petrol cap. He then went around the car checking and adjusting then and I asked him why as I'd just done them. He reckoned the fronts we too high and that although the petrol cap states the figures for 3 people and a piece of luggage, how often do you have that number of people in the car, usually its one. He also said that in his experience that inflating the to the book value with 99% of the driving being done with one person in the car could lead to premature wear of the front tyres. He was easy about the whole thing and the way we left it was the tyres inflated to roughly 34 psi all round and just keeping an eye on them. Seems to feel and drive fine but would be interested to hear others thoughts.

Cheers

 

[jonnysimm]

I have 34 all round and seems fine to me.

 

[RustyBucket]

Excellent, what are you driving?

 

[Sayam]

2009 A3 Sportback. 2.0TDi 170 CBBB engine with DSG. Book says 42 front and 36 rear.

I'm running 39 front and 36 rear.

Aftermarket wheels are 18 x 8J ET42. Not sure if that matters tbh

 

[jonnysimm]

I'm driving a 2010 a3 with 18 inch standard wheels. Seems fine might try abit more on the front if the book says 42 just seems very hight pressure.

 

[RPB]

TBH, I would rather do what Audi recommend than what he says. My tyres have just been measured again by Audi and are wearing at a similar rate across the whole width of each tyre and that is with the pressures as per the door sticker. 42F, 33R for my 2011 S3.
That is for the 3 people and cases but I do not know why I would change the pressures.
On my S3, the difference between 3 people and a full car and boot for the fronts is only 3psi, 42 unto 45 psi if full car and boot. So that tells me those pressures are at that because of the engine and not the passengers, so why would you just drop that to 34 psi?
The rears I can agree with totally. No point being over inflated if you are not carrying a full load.
Just my thoughts.

 

[shadow1993]

Probably gonna seem stupid but i run 40psi all round..

2.0tdi a3 (2004) on stock 16" alloys and some crappy tires. If inflated to the recommended the fronts look too squished so i usually pump up to a point where they are not squished and look all-right, which is around 40psi..

Am i being stupid? If i have anything under 40psi it feels like I'm driving an old boat or a 7 seater Chrysler or a sponge.. hence why I'm on 40ish psi.

Should i not do that?
Sorry to hi-jack the thread.

 

[jonnysimm]

I'm guessing it's to what ever you feel comfortable with aslong as the tyres can take the pressure then should be ok but 40 in the back doesn't it effect the grip in the wet ?

 

[shadow1993]

I'm guessing it's to what ever you feel comfortable with aslong as the tyres can take the pressure then should be ok but 40 in the back doesn't it effect the grip in the wet ?

Only thing i have noticed in the wet is that if the car is empty it will understeer in a sharp turn or bend but if car has 3 people in the back then the back will kick out in the wet.. not really sure what that means though. lol

 

[Phil-1]

I'm running 35psi front and 34psi in the rear on GoodYear F1 asymmetric, 18" wheels attached to an A3 TDI 170. I find the tyre wear and grip ok

 

[s3facelift09]

I never understood this, if there is a door sticker with recommended tyre inflating pressures by Audi. Why do someone make up their own tyre inflating pressure? I'm running 42 on the front, and 33 on the rear as recommended on MYS3 09, and everything is fine. But I don't see how it could be fine if I weren't running on recommended tyre pressures?

 

[Dan-Jnr]

I stick to what Audi recommend in the fuel cap. They designed and tested the car after all.

 

[kellogz]

I'm on 30psi all round for my b7 avant as per Audi recomendation

 

[RustyBucket]

Some interesting replies guys and I'm tempted to put them back to the values on the inside of the petrol cap, seems to make sense. Cheers

 

[audigex]

As far as I can tell, my car handles the same if they're within about 5psi of recommended in either direction... I do drive a Quattro on the lower black edition suspension, though, I'm not sure my car knows how to lose grip unless it's on ice, and even then things just tend to get a little light.

 

[veeeight]

Note that if you have XL rated tyres fitted - these have re-enforced sidewalls, and have to run at a higher pressure than non-XL rated tyres.

An XL tyre fitment as standard makes sense on a S3. With a low profile tyre, there isn't much of a sidewall. An XL tyre has reinforced sidewalls to cope with the additional lateral cornering dynamics, and enables the tyre to run at a higher inflation pressure to cope.
A non XL 88Y tyre, whilst having a lower static loading, hasn't got reinforced sidewalls!

Interestingly, a XL tyre inflated to the same pressure as a non XL tyre has a lower load capacity. A XL tyre must be inflated to, and run at a higher pressure than a non XL tyre to achieve the same load capacity. This explains why recent 8P's run at 42psi on the front.



Also:

The manufacturer recommended pressure will not necessary tie in with your objectives
Theirs is a compromise figure, for all round workability in a variety of different situations (eg: load, mpg etc).
If you are seeking maximum grip, for example, then a variance of pressure by a few psi will yield the results you are looking for (grip), at the expense of something else (wear).


More info on tyre pressures on A3/S3:
http://www.audi-sport.net/xf/threads/best-tyre-pressure-for-s3.184000/

 

[45bvtc]

Ooops...

 

[45bvtc]

STD tyre pressures for an RS3 (2-up) are 41psi front (255/30 19) and 39psi rear (225/35 19) rear but these pressures result in a lot of centre wear especially on the front tyres; so I run 39psi front 37psi rear and that gives an even wear across the face of the tyre and a better ride.