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I ran a tape measure on mine, 37" MTR's at 27psi on a 2 dr measured something like 36.1-36.2 somewhere in there.



I don't get it either. 15.5 x 2 is 31 + 17" wheel equals 48"?

SoK66

This is what's worked for me, as recommended by AEV when setting tire size with their Procal module. Lay a straightedge across the top of the tread of the driver front tire. At your street inflation pressures measure from the ground to the bottom edge of the strightedge. That reading becomes the tire size to enter into your calibrator of choice. When I ran MTR/Ks it seems to me the setting was something like 36 1/4" with full tread and 32 psi.

jtphoto JK

Measure from ground to center of hub and double it. That will give you the actual running height. Works every time.

Wrangeler X

This is 100% false.

The only way to get actual tire height is to calculate it from the rolling distance of the tire.

Mark a line on the tire at the bottom in the center of the contact patch. Then roll the tire until the line returns to the center of the contact patch. Measure the distance travelled (circumstance then solve for diameter.

Northridge 4x4

sea bass

How is that 100% false? This very simple process worked for me. It accounts for squish and got me close enough for my calibration.

There's more than one way to calculate "true" diameter.

sea bass

Duplicate :-)

jtphoto JK

The only way to account for the bit of squish is by measuring how i explained.
Don't believe me.. Try it for yourself before you call false.

jedg

Hrm... sounds like a science project. I might just do this on Saturday if I find time.

Measurement 1 (jtphoto JK) - Measure ground to center hub and double

Measurement 2 (SoK66) - straight edge across the top of the tire and measure to the ground

Measurement 3 (Wrangler X) - Mark center of contact patch on tire and ground. Roll forward until the mark on the tire is centered on the ground again. Measure that distance (gives circumference and calculate diameter).

I'll post the results for my BFG KM2s that are 35s on 17in rims.

Monte417

x2 this way has been working for me for years

Monte417

I bet your speedo is off at higher speeds. Get up to 75 80mph and compare your speedo to a gps. Under 60 you proably wont notice but the faster you go the more its off. You may be off 1-3 mph. That measurment seems high I had those same tires and my speedo is dead on. I believe I have 35.25 entered in which is also working for my 37" trail grapplers