Birchall
Dick Chown Award 2016
Hi Scott, as many people know on here I often spring to the "defence" of 17s especially since it really is virtually impossible to measure the difference in grip etc, because there are so many variables, it is all down to maths in the end.
The diameter of the tyres (16", 17") etc. does not really play any significant part in the grip offered in good or bad weather conditions. What does play a part is the width of the tread that contacts the road (185, 195, 205 etc.)
The more tread width that contacts the road the more that the weight is spread and so there is a mathematical reduction in grip in slippery conditions with wider tyres. In the dry, the more rubber in contact with the dry surface, the better (compare a race car tyre with a road car tyre).
That mathematical reduction in grip in slippery conditions really is small and the end result is NOT a noticeable difference.
Consider this from a mathematical point of view
A 195 width tyre as would be used on a 16" wheel (typically a 195 50 16 which is a standard size for the A2 with a similar rolling radius)
That 195 width equates to 7.68" wide
A 205 width tyre that would be used on the 17" 9 spoke alloys would use a 205 40 17, the tyre is 8.07" wide.
That is a difference in width of 0.39" (around a third of an inch or so)
So I would question how 0.39" on an (approx.) 8" wide tyre tread would transform the handling or grip of a tyre to any noticeable degree.
Much of the theory is correct, grip in slippery conditions would be impacted mathematically, but a extra half an inch of snow, or a few degrees difference in temperature, or a 1lb difference in tyre pressure would have a greater impact on grip.
So I am not saying anyone is wrong, I am just trying to point out that we are talking about TINY differences, So tiny that I am happy for my wife to have 17" wheels on her car, there are so many variables that I believe that this does not impact safety (and also why would Audi and other manufacturers offer a car with an unsafe tyre / wheel size). I personally run 18" wheels and 215 35 18 tyres and the THEORY is that this would make the car feel like it running on stone tyres, but it really doesn't, the 18" tyre wall is only 1" thinner than the standard 16" tyres. Does that impact the ride, yes of course, does it significantly affect it, no. The 215 width means that there is a slight mathematical loss of grip in slippery conditions too, but in ice and snow I don't drive at all, or if I have to I drive well within the conditions.
I really like the look of 17" (or larger) wheels on an A2 and I like the improved steering response and reduced roll that I get (albeit tiny mathematically) and so when people who want to use that size are worried by the difference, look at the maths. Because people will have their own views and impressions of how hard the ride is etc. and that is very subjective (and also depends on the tyre pressures etc.) Everyone is, of course entitled to their view on this and I m not actually disagreeing, I am just saying that it could be that the difference in ride comfort is not quite as bad as it would seem.
Steve B (ready for the responses to this!!)
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