# Math question

• posted on October 24, 2003, 6:40 am
Ok here it goes, knowing your tire size, your engine rpm, your trans drive gear, and your final rear end drive gear, how do you throw those together to
I tried rpm/trans gear/drive gear*tire size in inches/the number of inches in a mile* 60(the number of minutes in an hour since its rpM). What am I doing wrong, or not seeing right?
I found calculators on the internet for it which work great, but I want to be able to do the math myself, without having to run for a computer. \$5.00 Solar crappy calulator, maybe.
Brian

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• posted on October 24, 2003, 2:42 pm
what website did you use? I don't know the formula, but maybe we can jack it from the JS in their pages :-)
Travis

to
\$5.00

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• posted on October 24, 2003, 9:08 pm

drive
together
inches
I
to
I can send you a Excel spread sheet and you can steal it from there.
Al

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• posted on October 25, 2003, 2:14 am

it s RPM= MPH x GR x FTR x 336 / TD
RPM = well RPM MPH = well MPH you want to see the rpm at GR = gear ratio FTR = final trans ratio if you are going to using overdrive 336 = magic number for it to work out right TD = tire diamter
moderator at www.fl-thirdgen.org

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• posted on October 25, 2003, 3:39 am
MPH=Tire Radius/168 * RPM/Gear Ratio RPM8 * Gear Ratio * MPH/Tire Radius Gear Ratio= Tire Radius * RPM/168/MPH Tire Radius8 * MPH * Gear Ratio/RPM
Bird79 1979 Firebird Esprit 1973 455 YC

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• posted on October 26, 2003, 1:44 am
Dang, thanks for all the replys. :)
Brian

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• posted on October 28, 2003, 9:54 am
On Thu, 23 Oct 2003 23:40:25 -0700

Make sure the tyre size is the tyre's circumfence and NOT its diameter or radius. If you use a radius, you will need an additional 2 * PI in there.
ALSO: tyres slip at high speed. And I believe that they slip a lot. Over 10% I believe.
Bram