Recalibrating Speedometer?

[JimmyTwoTimes]

So, I'm thinking of going with 18" wheels for my winter tires, since it's easier to find 18" winter tires than 19". What I want to know is, do I have to recalibrate the speedometer to account for the differing wheel size? How would I go about doing that?

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[Grimace427]

The diameter of the wheel is irrelevant as long as the overall tire diameter is the same or at least close.

Use this calculator: http://www.rimsntires.com/specspro.jsp

 

[JimmyTwoTimes]

That is a fantastic calculator; thanks!

 

[D BERRY]

The diameter of the wheel is irrelevant as long as the overall tire diameter is the same or at least close.

Use this calculator: http://www.rimsntires.com/specspro.jsp

How exactly does the ECU calculate speed and mileage, does it measure it using the ABS sensor. If not how is it done? My reason for asking isn't speedometer calibration but odometer calibration. My car is leased, so if I put gears in my car and keep the same tires, is my car going to record the correct mileage because my tire revolutions per mile remain the same. I'd like gears but don't want to give up the miles I'm entitled to.

 

[Clarkson]

How exactly does the ECU calculate speed and mileage, does it measure it using the ABS sensor. If not how is it done? My reason for asking isn't speedometer calibration but odometer calibration. My car is leased, so if I put gears in my car and keep the same tires, is my car going to record the correct mileage because my tire revolutions per mile remain the same. I'd like gears but don't want to give up the miles I'm entitled to.

I would say it counts RPM x set wheel diameter

 

[Need4SpeedMotors]

I would say it counts RPM x set wheel diameter

correct

and its from the rear that it bases this .

 

[D BERRY]

So if I change gears but keep the same tires then my speedometer and odometer will be correct, right.

 

[Road Dog]

That is correct. So if you put taller tires on you could get in some extra miles.

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