mph rpm ?

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Dec 22, 2006 | 11:04 AM

dmaaero

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From: wilmington nc

mph rpm ?

if i'm turning 2350 at 55 mph what kinda gears do you think i have?

Dec 22, 2006 | 11:07 AM

Big2Bird

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What is the diameter of your tire?

Dec 22, 2006 | 11:07 AM

Wrecked82

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From: Texas

My speedo says I an going about 95 at about 2400 rpm, but that is because I changed from a 2.89 to a 3.55 and have not changed speedo gearing yet!

When I had the 2.89, 55 would have been about 1700 rpm.

Dec 22, 2006 | 11:19 AM

dmaaero

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From: wilmington nc

p255/60r15 26 inch diameter

Dec 22, 2006 | 11:20 AM

Big2Bird

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IF your tach and speedo gears are correct, you have 3.55.

Dec 22, 2006 | 11:24 AM

dmaaero

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From: wilmington nc

thanks bigbird

Dec 22, 2006 | 12:07 PM

JIMS1970VETTE

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What is the formula to fiqure it out?

Dec 22, 2006 | 12:40 PM

Big2Bird

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RPM=MPH x ratio x 336/Tire diameter

For those who are mathmatically challanged, go to unitrax.com, and use their computer.(Like I do)

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Dec 22, 2006 | 01:00 PM

Glensgages

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From: State of Confusion

Quote:

Originally Posted by dmaaero

if i'm turning 2350 at 55 mph what kinda gears do you think i have?

Quote:

Originally Posted by JIMS1970VETTE

What is the formula to fiqure it out?

This is the formula I have used for many years:

GEAR RATIO = RPM x .9 (if using a non-locking torque converter ) x .006 ( a factor, incorporating pi ) x 1/2 TH (tire-height ) divided by MPH x OD/R (over-drive ratio, if any ).

If your 255/60R15s are 26" tall (mine are slightly-taller than 27" ????? ), I would estimate your rear-gear ratio at close to 3.00:1, 'assuming' you are running a THM350/400 w/o a locking converter.