7degrees is the recomended will not harm the tyres even if you use them in summer.

Mine is a 2004 B6 that came with 17" alloys. In the original brochure, the base model came with 15" wheels, so I knew they would fit round the brake callipers. Audi Guildford were helpful on the phone confirming the right part number/offset etc and the wheels were delivered (to them for collection) within 48 hours even when the weather was like this a couple of weeks ago.

Today I was able to try out the new tyres properly. All I can say is they are fantastic, very good traction for pulling away and braking. Aggressive throttle was needed to get the ESP light to flash and only hard braking triggered the ABS on quite bad side roads that had all sorts of vehicles stuck or wheels spinning.

I drove down several side roads where the foot thick snow was untouched and I could hear it rubbing on the bottom of the car. The tyres performed very well. The packed ice/snow on small hills near me had many motorists struggling and trying to resist being smug I wound my way through the stranded vehicles.

They seem up to anything a UK winter might throw at them.

How are you doing the calcluation? I think the contact area will be the same - just a different shape, i.e. longer rather than broader.

I don't think the tyre will be squashed more on the road surface, the footprint looks approx square on the 195 and 235 tyres, hence my calcs of 19.5x19.5 vs 23.5x23.5cm

It also seems that your rolling circumferences between the 2 tyres (i.e 195 & 235)
- given your measurements - are nearly 170mm different. So something not quite right I'd say.

Firstly, another error crept in - the summer tyres are 235/45/17 not 235/55/17 hence the concern that I'd altered the diameter of my rubber.

To answer the points above, the 195 and 235 dimensions are the width across the tyre tread in mm so don't affect the rolling dimension. It's the profile of the tyre vs the rim diameter that changes this and 235/45s on a 17" rim measure 64cm dia (circumference approx 200cm) and the 195/65s on a 15" rim also measure 64cm so have the same circumference/ride height etc.

Using a calculator such as the one at www.tyresave.co.uk/tyresiz2.html, it shows a very small discrepancy, one approaching the tolerance in a tyre diameter between new and part worn and one I couldn't even differentiate myself with the two wheels side by side.

Now where's that edit button?

contact patch area = weight / tyre pressure

Thanks for that info, I didn't know that.

I'd also make sure your Ins. Co. understand you've not just changed the type of tyre, but also the size of the tyres & rims themselves - they may have just heard 'winter tyres'.

Yep, all done, and in fact it felt easier telling them I bought the wheels from Audi as they specified them for my car rather than explaining I'd bought a set from Ebay that I know would fit. I confirmed that our conversation was recorded as proof of notification even though they said no confirmation was needed.

As an update to this thread, we toured the Cotswolds over Christmas and the car behaved remarkably. Temperatures were down as low as -8C with a heavy covering of snow on the lesser used roads but this was no problem for the Audi with the winter tyres fitted.

In my experience driving many types of vehicle over the last 35 years, fitting winter tyres has been the single biggest improvement I have seen. The car was able to navigate lanes where only tractors had passed with the ESP light only occasionally flickering and the ABS only kicking in on patches of ice.

When it was clear and safe to do so, I deliberately pushed the car, both to go and stop and was very impressed with the performance of these tyres.

As they are slimmer than the regular fit and are more flexible at low temperatures, the road noise is greatly reduced even driving on clear dry roads.

The temperature has now been regularly above 10 degrees for the last week or so, it may be time to swap back though I will miss the appearance that my car has had all the alloys nicked!

Spending +/- £450 on the rims/tyres was money well spent and gave me the confidence to go anywhere this winter without the fear of getting stuck.

Edited by Mutton Geoff on 06/02/2011 at 17:01