Smaller circumference winter tyre question
Discussion
My 2009 model A6 came with OE wheel tyres were 255/35 R19. I have now fitted new 18" wheels with 235/40 R 18 winter tyres, I had forgotton about the narrower tyre with regards the profile %. According to online circumeference calculator I have a 2.4% smaller overall circumference. I realise Speedo will over read, and mileage will be exagerated, but will the car otherwise be OK?
The speedo may over read, but I think the miles will still be accurate, some sort of correction using ECU and tyre speed sensors or something I think.
Otherwise, how would the cars which can be specced with different sized wheels from the beginning cope ? They are not going to re-calibrate each individual car.
Might be wrong, but that's what I remember reading somewhere.
Otherwise, how would the cars which can be specced with different sized wheels from the beginning cope ? They are not going to re-calibrate each individual car.
Might be wrong, but that's what I remember reading somewhere.
sinizter said:
The speedo may over read, but I think the miles will still be accurate, some sort of correction using ECU and tyre speed sensors or something I think.
Otherwise, how would the cars which can be specced with different sized wheels from the beginning cope ? They are not going to re-calibrate each individual car.
Might be wrong, but that's what I remember reading somewhere.
Pretty sure that's wrong, if all 4 tyres are reduced by the same amount, unless the car has gps calibration, ride height sensors or some kind of laser measure from the wheelarch the ECU is not going to know you've put smaller diameter tyres on. The wheels will be spinning faster for a given road speed but the ECU etc will just assume you're going faster than you are, and miles covered will be calculated in the same way that speed is, usually from a sensor in the gearbox.Otherwise, how would the cars which can be specced with different sized wheels from the beginning cope ? They are not going to re-calibrate each individual car.
Might be wrong, but that's what I remember reading somewhere.
Edited by LocoBlade on Sunday 28th November 14:43
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