hammer71

Probably beating an old horse here...got a st of 33'"'s and measured them under load with 32 psi-from ground up actual 31.50?Seem coorect ,as I have searched a bit and see it is common for offroads to measure smaller.Question being-what is the best way to get actual height or diameter?speedo seems to be on with gps but will it throw odomoter out?

thanks in advance

vandegrift

I was told by a shop to make the measurement with the tire off the ground so you get the full height, due to the tire flexing out to full diameter when rotating. I measured mine out with out load and it seems to be right on.
Good Luck

cppower

Measure from the center of the wheel to the top of the tire and multiply by 2 for an unloaded measurement.
Top of the tire to the ground for a loaded measurement.

The tuners use a loaded circumference to do their calculations derived from the loaded diameter you provide.

ffjeeper

The best way to get the actual loaded height of the tire is to measure from the ground to the center of the wheel hub and multiply x2. This takes into account the flex of the tire as it rolls. I did this when I was tuning with my SC and it was spot on.

Red

The most accurate way to measure actual tire size is to mark the side of a tire with chalk at the bottom where it contacts the ground, and then mark the ground as well. Then roll the Jeep forward until the tire has one full rotation, i.e. the mark on the side of the tire is now on the ground again. Mark the ground where the chalk mark on the side wall is. Now measure between the two points on the ground. This measurement is the circumference of your tire. Now, remember what your math teacher taught you back in, I don't know, 8th grade. c=2πr. So, divide the circumference by π (pi = 3.14) and you have the diameter of the tire. And you thought you would never use math again. This method, by the way, accounts for vehicle weight on the tire and the deformation of the tire while rolling.

cppower

Doesn't the superchips manual state to measure from the top of the tire to the ground at the highest point? That way it can calculate the loaded circumference it needs for it's adjusments.

cppower

That is the way to get the most accurate loaded circumference which can then be converted into a loaded diameter.
If you are trying to determine if the 35" tire you just purchased is the size you thought you purchased, then you need an unloaded measurement.

ffjeeper

I think it does. After doing a couple of searches on it and reading a couple different forums the method that worked for me the best was to measure from the ground to the center of the hub. Dead on accurate for me. I did try a couple of other methods including the one in the manual all were off by 3-5mph. I checked with GPS and radar.