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2000 Tire size and Speedo/Odometer

Blown

Elite Explorer
Joined
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City, State
Montrose, CO
Year, Model & Trim Level
2000 X-Edge
I am getting better mileage than I thought. Whohoo! At least a half MPG more. At 72.31 MPH the speedo is reading 70 at 90 almost 93!

I forgot about the fact that Forscan will only allow up too a 265/75 -15 658 revs/mile.

I put on 265/75 16's, set the Speedo in the GEM module with Forscan to the max (265/75 -15), and my speedo is off by what you would expect, reading about 3%.

Ran my tire size calcs here: Tire Size Calculator
 



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From the several 2nd gens and combinations of tires I have used, 30" is about exactly what the speedometers are calibrated for.

So don't go by the OEM tire size, regardless of whether it was 15" or 16" wheel sizes. Use 30" as the goal size, and calculate your actual tires sizes compared to 30" tires. That percentage is what you should need to alter the reading by. Does the Forscan give you that option, alter the VSS signal by a ratio amount?
 






Forscan gives you tire sizes, a pick list. The max size is 265/75 -15 658 revs/mile. I think they/Forscan only calculated what would fit stock X's.
 






Gotcha, I was hoping it would be like the old school calibration device, but by software.
 






The higher end 2nd gens came factory with 255/70/16s. I don't know offhand how that compares with a 265/75/15.
 






That would be closer, only 1.6% off.
 






The higher end 2nd gens came factory with 255/70/16s. I don't know offhand how that compares with a 265/75/15.

That the stock 30" size for most 98-01's, most accurate speedometer result.

The 265/75/15 is 1.5" taller than the old stock 235/75/15(29"), so it's a 30.5" tire, close to ideal, will read a bit slow on the gauge.
 






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