31s speedo gear?
08-15-2012, 09:04 AM
#1
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Location: Commerce, MI
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Year: 1988
Model: Cherokee
Engine: 4.0
31s speedo gear?
stock tire from the door sticker is 215 75 R15 diameter 27.7"
new tires are General Grabber AT2s 31x10.5 R15 diameter 30.8"
31x10.5/15 = 267/76/15
3.1" difference. The speedo on GPS is between perfect and 3mph slow on expressway. But the calculators say it should be 10.7% slow.
Question is what gear should I replace the stock one with?
My plan is to start tracking 1 tank of gas with the phone GPS and compare the miles to my trip and take that percentage difference. Right now for mpg I am only adding 5% to the miles, because I don't think its 10% off.
new tires are General Grabber AT2s 31x10.5 R15 diameter 30.8"
31x10.5/15 = 267/76/15
3.1" difference. The speedo on GPS is between perfect and 3mph slow on expressway. But the calculators say it should be 10.7% slow.
Question is what gear should I replace the stock one with?
My plan is to start tracking 1 tank of gas with the phone GPS and compare the miles to my trip and take that percentage difference. Right now for mpg I am only adding 5% to the miles, because I don't think its 10% off.
08-15-2012, 09:12 AM
#2
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Join Date: Mar 2012
Location: Bellevue, WA
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Year: 1998
Model: Cherokee
Engine: 4.0L
Check speed with GPS to verify % difference.
Gear speedo tables are posted everywhere.
Gear speedo tables are posted everywhere.
stock tire from the door sticker is 215 75 R15 diameter 27.7"
new tires are General Grabber AT2s 31x10.5 R15 diameter 30.8"
31x10.5/15 = 267/76/15
3.1" difference. The speedo on GPS is between perfect and 3mph slow on expressway. But the calculators say it should be 10.7% slow.
Question is what gear should I replace the stock one with?
My plan is to start tracking 1 tank of gas with the phone GPS and compare the miles to my trip and take that percentage difference. Right now for mpg I am only adding 5% to the miles, because I don't think its 10% off.
new tires are General Grabber AT2s 31x10.5 R15 diameter 30.8"
31x10.5/15 = 267/76/15
3.1" difference. The speedo on GPS is between perfect and 3mph slow on expressway. But the calculators say it should be 10.7% slow.
Question is what gear should I replace the stock one with?
My plan is to start tracking 1 tank of gas with the phone GPS and compare the miles to my trip and take that percentage difference. Right now for mpg I am only adding 5% to the miles, because I don't think its 10% off.
08-15-2012, 09:49 AM
#3
CF Veteran
I think you need a 32 tooth gear. You have a '98 XJ? I have a couple of gears, but they're long shaft. I suppose your gear is the short shaft.
08-16-2012, 09:32 AM
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