Chris, Graeme, thanks.
I do seem to recall reading a classic car mag article a while back that said 1960s/70s standard tyres usually had 80-85% profiles. Unfortunately, can't find the article amongst various stashes of old magazines around the house
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I tried to do some quick calc's to see what the difference in overall diameter (OD) between 82% 165s and 80% 175s might be. With the tyre fitted to a 14” diameter wheel:-
OD for 165/82/14 = ((0.82x165)+(14/2 x 25.4))x2 = 626.2mm
OD for 175/80/14 = ((0.80x175)+(14/2 x 25.4))x2 = 635.6mm
Difference = 635.6 - 626.2 = 9.4mm
Given the slight bulging you seem to get with 175s on a rim designed for 165s, as Michael mentioned, I suspect that (assuming the same inflation pressure for both tyre sizes), the actual difference will be less than 9.4mm? Also, given that tyres wear in tread depth over their life by a few mm, I reckon the difference between 165/82s and 175/80s will be negligible. This corresponds with Michael’s “rolling radius only about 1mm difference” (or 2mm OD).
Another question for the experts:- as per previous post, the 2200 owners manual lists “175 SR x14 Avon Snow Grip Radial” as an acceptable winter tyre. I assume the "SR" is the speed rating (112mph?). However, what was the profile of this 175 tyre? If it was a 175/82, the OD of the fitted tyre would have been greater than a modern 175/80? Unless, you operated it at lower inflation pressure (common trick on snow) or maybe the older tyres had weaker walls causing it to bulge out more and reduce the OD?