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Do I need to recalibrate my speedometer when fitting smaller wheels to my Ford Mondeo?
I have a Mondeo Ghia 2.5T with 18-inch wheels and am seriously considering wasting some of my children's inheritance by switching to 17-inch (plus tyres of course). My concern is that a Ford main dealer advised me that this would necessitate re-programming the computer controlling the speedometer. Given the frequency of your advocacy of this wheel change, could you confirm or refute this advice? My own view is that the rolling circumference would remain a constant in going from 235/40 R18 to 235/45 R17.
Asked on 11 May 2013 by PHB, via email
Answered by
Honest John
All that is important is the rolling circumference of the tyres. Usually deeper profile tyres on smaller diameter rims are an almost exact match. You can check with a tape measure. If not they may even compensate for the fact that most car speedometer read around 5 per cent fast.
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