Ask Honest John

Honest John Ask Honest John » Do I need to recalibrate my speedometer when fitting smaller wheels to my Ford Mondeo?

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.

From choosing the right tyre to what to do when it goes wrong - we have the answers.

Tyre News And Advice
Similar questions
In your reply to HH of Salford on 29 December you advised him to replace his 22-inch wheels with 18, 19 or 20-inch wheels. If he (or she) does that the speedometer and trip meter would be reading higher...
The ride in our 2010 Mondeo Titanium diesel estate is quite harsh for my wife who has a bad back. Could I improve the ride by fitting different size wheels and tyres and what tyres would you recommend...
My Mondeo is on very bling 19-inch rims. I was thinking of ordering smaller wheels from My Tyres, which you have mentioned, but someone suggested that if I come down to 16-inch or 17-inch rims the bolt...
Related models
Very good to drive. Refined and comfortable to travel in. Massively roomy cabin and huge boot. Reasonable value. Efficient ECOnetic and EcoBoost models.