I agree that the factory pressure recommendations are a bit overrated. After
a lot of testing I found that the best grip in my A4 can be obtained at 2.1
atmospheres (cold tyres), which is two tenths down from spec. I imagine
factory recommendation tries to make up for some possible short term
neglect. It's hard to believe how much more comfort and stability you can
get from that tiny adjustment.

On another note, a few years ago, I had my winter tyres installed but some
green mechanic set rear pressure at a whopping 2.8 atm. As I was not aware
of that and I'd just collected the car, I nearly had an accident when
overtaking at some 140 km/h, when the car exhibited a severe instance of
oversteering all of a sudden, which had never happened before.

Basically, what happens when you overinflate the tyre is that the contact
surface decreases with more stress on the central part of the band, and
general "nervousness" as exhibited by the car. This translates into sudden
unpredictable behaviour. The only slight advantage if you drive slowly is
that less contact surface means slightly increased mileage. And yes, I do
know that theoretical physics will tell you that friction force is not
dependant on surface, but in the real world it does make a difference.

Underinflating can be even more dangerous, especially in the summer, when
driving at high speed on the motorway could potentially cause the tyre to
burst because of increased friction causing rubber temps to soar. Even if
that doesn't happen the tyre gets quickly worn out and mileage may decrease
dramatically.

Basically, I would suggest trying some tenths down at low speed and check
grip. There is no doubt that optimal pressure equals the best possible grip.
Then, on those instances when you're planning to see rather a lot of the
motorway get those tenths back in.

My two cents,

JP Roberts

Audi has been critisized in the UK for their poor suspension
performance. Audi now has focused a team to resolve to the UK market.