There is well documented evidence that the wider a tyre becomes (in relation to track and tyre diameter) the better the outright grip is - at the expense of ride [comfort], steering-feel and noise - not to mention expense. The fashion-police drive manufactures and joe-public to demand "performance" and cosmetic-appeal. The result - bigger and bigger tyres with smaller and smaller profiles...

The '02 A6 Quattro Sport is fitted with 235/45/17 tyres as standard. The ride-quality on poor surfaces is harsh. This is due to the firm "fast-bump" shock absorbs ion of the suspension setup and wheel/tyre configuration. Bumps with quick changes of elevation such as pot-holes, ruin the otherwise tranquil progress. Larger bumps, or bumps with slow changes in elevation are ridden over without problem due to "slow-bump" characteristics. I don't know how the roads are around you but for me they contain many irregularities which can make the tyres feel as if they are made of solid rubber. These particular bumps send shock waves throughout the chassis which is most unpleasant – unpleasant to the point that I was actively scanning the road ahead to route the smoothest course.

The options are essentially retuning [replacing] suspension items and/or replacing tyres/wheels. As the suspension changes would have been expensive I opted to explore the wheel/tyre option. Obviously, narrower tyres are required with larger profiles. It is important to ensure that overall diameter is maintained to avoid speedometer errors and potential? Quattro drive system problems so sticking on any old combination is bad news. As it turns out a 215/55/16 tyre is almost spot bollock on - just fractions different from the original 235/45/17.

I bought 4 new 16" alloys fitted with 215/55/16 tyres and the results are very good. If you could imagine running over a bump that has near vertical edges and think how that feels. With the new setup, it is as if the edges have been rounded-off. That is to say that you still feel the bump but it is nowhere near as violent resulting in a better ride. Steering feel and turn-in is improved, noise is reduced. Grip is slightly reduced, and certainly on very high speed bends on smooth tarmac the oe tyres/wheels instil more confidence. Every where else, grip is still superb with the added "fun" characteristic that the tyres emit a dull squeal as the grip limits are explored which never happened before - I guess this is due to the greater pressure applied per square inch than before. The other real benefit of narrower tyres is of course that they are less prone to aqua-planing and provide better grip in icy conditions.

Useful links:

http://www.orbweb.net/autoshop247/ty...tment.html#top (general advise on tyres/wheels - profiles, sizes etc.)

http://www.torquecars.co.uk/Tuning/alloy-wheels.php (useful tool to calculate tyre/wheel combinations and effect on overall diameter - important to avoid speedometer errors).