RPMs aren’t lining up with GrimJeeper gearing calculator

mrblaine said:
That math has no margin of error. It is simple and basic as 1 x 5 = 5. There is only one variable and that is the entered tire size which most get incorrect. If you want to know the tire size, keep changing until the RPM matches the specified MPH in the correct gear and that tells you your tire size actual, not what's on the sidewall.
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That’s what I was getting at, I just didn’t word it correctly. The tire measurements are indeed the variable.
 
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Bbrayden85 said:
Yea figures. Its a 31” tire but only about 30” actually
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On mine using Blaine's method, a brand new 35" MTR works out to 33.875" in order to get the correct calculation. Measuring the hub height is very very close to that because I can't measure that precisely on pavement.
 
Bbrayden85 said:
From stock tire size it is. Measing from the ground to the hub then foubling that is 28.5. Put that into the calculator and its 2400 rpm at 60
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If you have the other info correct, speed, RPM, trans, and gear ratio, the only variable is tire size. Change the tire size until what the calculator says matches what the dash says and that is your actual tire size.
 
mrblaine said:
Why are you silly enough to believe that a tire doesn't squash when you put weight on it?
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Huh. I measured the sides. That dont have weight. With the vehicle off the ground. Then measured hub height. With the vehicle on the ground. Do you just come to strt arguments because you’ve contributed nothing to this.
 
Bbrayden85 said:
Huh. I measured the sides. That dont have weight. With the vehicle off the ground. Then measured hub height. With the vehicle on the ground. Do you just come to strt arguments because you’ve contributed nothing to this.
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No, the arguments start when folks don't want to believe they are wrong. Can you math, at all? All the calculator does is multiply gear ratio by trans ratio, by tire size to give you engine RPM and MPH. The ONLY fucking variable is tire size.

That is predicated upon your observations of RPM and MPH being accurate. If they are not, then that is something else you fucked up.
 
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jjvw said:
On mine using Blaine's method, a brand new 35" MTR works out to 33.875" in order to get the correct calculation. Measuring the hub height is very very close to that because I can't measure that precisely on pavement.
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Use a trammel point, it can be accurate to .010”
 
astjp2 said:
Use a trammel point, it can be accurate to .010”
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I don't need to measure. I just keep changing the tire size in the calculator until it matches what I see on the dash after I verify that the speedo is correct. That gives me the exact tire size that matters.
 
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