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107 Posts
Discussion Starter · #1 ·
Hey Everyone,

I just got a new set of 255/75R17's to upgrade my bald 225/75R16's and with the change in tire size; I had to calibrate the spedometer. I got a Superchips flashcal and that is as easy and intuitive a piece of equipment as anything, but I noticed that even though the programmed tire size is slightly off (32.00" vs actual 32.1") the spedo is reading 68 MPH vs the GPS reading 65. Definitely not the error I was expecting, especially since I put in a smaller diameter.

The build sheet says I've got a 3.21 diff ratio, and I re-plugged that into the flashcal to verify it was right (same etror). But the math says I've got a 3.07 diff ratio...

I'll crawl under the Jeep tonight to see what I can find, but does anyone else have any experience with errors on the build sheet?

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