I have a 97 Expedition 4x4 which initially came with 275-60-17 tires. I recently replaced the set up with 275-45-20. I noticed that the speedo say I am going faster than I think I really am. I referenced to the other postings about changing wheel sizes and its affect on the speedo. I know someone recommended changing the gear in the tranny from a 20 tooth to a 17 tooth for those who went for a larger set up. Am I right that I should change the gear to a 22 or 23 (whatever is available)?

Also, I know the person also said it takes 5 minutes. Can you please help me out with info on how to do it? Do i need to drain the fluids? or is it as easy as 1, 2, 3?


Thanks

 

I remember someone telling me awhile back what they did but...damn I forgot bec my tire height was not to off, but I do remember he took it to a speedo shop etc and they just put a box of some sort in and recalibrated the speedo. Someone here gotta know? I think on the 99up you can just use the computer plug to change it or if you get a Superchip they can fix it? sorry I had no exact answer. E-Mail Roger from the Online store he would know or help.

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My truck at:

http://www.streetscenemag.com/ViewOw...?ProfileID=202

 

Isturbo79,

You can either:

Get your speedometer adjusted, but... What are you going to do if later on you decide to get a different size (i.e. 275/35/20)? Do the calibration again?

Or the easy way, which is what I'd do. Go to this page: http://www.dakota-truck.com/TIRECALC/tirecalc.html
Enter the size tire you truck came stock and also enter the new size. You'll get a table that tells you the actual speed (at which your speedo was originally calibrated) and the speed with the new size. I can see that the difference is not huge, barely .54 mph faster going at 65. This is far easy (for me at least) than messing with the speedo.

Alf