Quote:
Originally Posted by eco-jeeper
I don't believe in using GPS. I'm like a non-violent Neoluddite - I don't even have a smart phone.
31 in. tires / 27.7 in. tires = 1.12 (times faster than speedo)
60 MPH * 1.12 = 67.2 MPH
I drove a mile on the interstate at exactly 55 MPH speedo (55*1.12 = 61.6 MPH), it took me 59 seconds between mile marker signs.
Looks like my variance is less than one percent or so. I realize there will be some discrepancy but that is inevitable. -1% MPG would still be higher than 28 MPG.
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You assume that the speedo and odo are calibrated the same, they're not on any vehicle I own.
Your odometer was accurate from the factory to about 1%, it probably now under reads by ~10%.
When you put 31's on a standard Jeep XJ/TJ, you end up with an accurate speedo (about 1% over reading), but the odo now under reads by around 10%.