Entirely correct
As a weekly reader of your column I often see you advise people to change wheel sizes to avoid a certain problem. Would this not affect the speedometer reading, thus making it illegal unless the gearing was altered to compensate?
Asked on 24 July 2010 by TS, Newark
Answered by
Honest John
You have to keep the rolling circumference within 2.5%. Smaller wheels allow the fitting of deeper profile tyres. Go to: www.etyres.co.uk/tyre-size-calculator.htm and you’ll find that 225/45 R18s are approximately equal to 215/50 R17s, which are approximately equal to 205/60 R16s.
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