Ford and Tire/Wheel Sizes

93SuperCoupeBoy

Registered User
After pondering and my computer screen and thinking way over my own capacity, I've found something I have a question about.

Ok, the factory tires on a 15" rim (assuming 205/70R15 tires), is 26.29".

The factory tires on a 16" SC wheel (once again assuming 225/60R16), is 26.62".

So, based on this, does Ford have some remedy for the differences in the speedo on the cars with these varying tires? Is the complete drivline the same? I'm also assuming that these cars would have the same rear axel and other things like that. Just wondering, nothing important anyways, but it is an interesting topic!
 
When there is only 2% or less variance in tire diameter, Ford often will use the same tooth count speedo gear on the applications. Most automotive speedometers are off by as much as 5% anyway, so a 1 or 2% variance due to tire rolling diameter is not going to be noticeable. For larger differences, Ford has speedo gears with different tooth counts.


cheers,
Ed Nicholson
SCCoO
 
fast Ed N said:
Most automotive speedometers are off by as much as 5% anyway

cheers,
Ed Nicholson
SCCoO

I have read that they can be off up to 20%. Is there any truth to that?

Russell
 
I know we had some Windstars for a few years that were off as much as 10%. Haven't heard of any being off by 20%. I believe there are federal government guidelines for speedometer accuracy, I doubt that 20% would be acceptable.


cheers,
Ed N.
 
I believe the law states that speedometer must be accurate within 10%. I had just heard (you know how accurate that is ;) ) that tidbit about the speedo accuracy. Thanks for the info.


Russell
 
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