Tire Size Calculator out by 5%?

Has anyone else been having this problem lately? We been setting the tire size to the customer supplied size and on 3 or 4 different occasions now it has been out by 5%. I dont have the trucks on hand so I couldnt confirm the actual size of the tire (I asked them to check, waiting to hear back).

One customer has his tire size set to 31.75" with a ppe yet we set it with the efilive calc and it was 31.7, so it all seems good, but yet they are saying it is now out by 5% and the tire size we supplied with that adjustment is 30.2". The rear differential is 3.73s and confirmed.

I find it just so odd that the PPE would be happy at that OD and efilive needs a different one. Not sure how that would even be possible, that said I have not confirmed this in person, only going off what I am being told.

Just curious if anyone else has seen this on their day to day work? Seems odd.

I always do it by tire height, or I look up the tire, and get the rev's per mile from the manufacturer to plug in. The calculator has always been off for me.

I always ask for an exact measurement

It's been my experience that the factory calibration is always off a little bit. I figure it was GM's way of a fudge factor to make it work out. When doing tire size changes, I always start out with the GM calibration value (already fudge factored) and do the relative size correction. So far, this has worked everytime.

:thumb_yello:

I had to use what the manufacturer says for revs per mile. it is about 1/2 MPH off according to GPS