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EmptyGarage's Avatar
 
Join Date: Jul 2009
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Gear Ratio Calculator

I have a non-stock ring & pinion and would like to reproduce a chart similar to the one pictured. I'm assuming that this is a printout from an excel spreadsheet. Does anybody have a link to a gear ratio calculator. This one includes tire diameter which I think is critical.

This chart also would give a good indication of effect of tire size on actual speed vs speedometer reading.

Old 08-06-2010, 06:36 AM
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Gear Ratio Calculator - Porsche 993 Turbo
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 08-06-2010, 07:29 AM
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Thanks.

Anybody know of any others . I'd like to cross reference at least two just to be sure calculations are accurate.
Old 08-06-2010, 08:52 AM
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it's simple math.

speed x 336 x final drive ratio / tire diameter = rpm
Old 08-06-2010, 10:29 AM
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hmmmmm...

tire diameter x rpm / 336 x final drive ratio = speed

what is the 336?
Old 08-06-2010, 10:46 AM
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The constant

120mph x 336 x 2.63 (4th gear x R&P) / 24.5 (tire dia) = 4328 rpm
Old 08-06-2010, 02:02 PM
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Quote:
Originally Posted by drmatera View Post
The constant

120mph x 336 x 2.63 (4th gear x R&P) / 24.5 (tire dia) = 4328 rpm
somebody's got some 'math' skills!
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 08-06-2010, 02:56 PM
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haha, I can't take the credit for that. Hell I had to forget 3 things of mid level importance just to remember that formula
Old 08-06-2010, 04:58 PM
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