7131 tire adjust

[JIGSAW]

I've updated my predator, and adjusted the tire size (35"). However, it seems like my speedo is now reading FASTER than I'm going, according to my GPS. Plus, with the tire adjust, my signal light "blinker" is very very slow. anyone else have this problem?

[lpennock]

How did you enter the tire size? Did you enter it by the side wall size, if so the predator incorrectly calculate the size of the tire. Did you enter off the advertised size? If so you need to calculate based on rolling diameter, rather than static diameter. Rough difference between static diameter and rolling diameter is the rolling diameter is 97% of the static diameter. An example the static diameter of a 275/70-18 is 33.2" if you just enter 33" for the tire size or that tire size in the predator you speedometer will be off about 2 MPH at 70mph. If you apply the .97 correction factor you will get a calculate size of 33.2". If you then enter 33.5" in the predator your speedometer will be too close for you to tell the difference.

Diablo you listening? You need to fix the enter by sidewall size to take in to consideration the difference between static diameter and rolling diameter.

[mikel]

Interesting, I was not aware there was a problem, we'll check it out....

[lpennock]

one correction to my post. The static diameter on the 275/70-18 is 33.2 calculated and the rolling diameter using the .97 correction factor is 32.2 so the size that should be entered is 32.5 not 33.5.

BFG lists the AT KO at static diameter of 33.19 and the revolutions per mile at 627 which matches the .97 correction factor. Lower profiles series would probably need a smaller correction factor.