Thread: another gear ratio ?
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05-16-2015 05:37 AM #3
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- Car Year, Make, Model: '33 HiBoy Coupe, '32 HiBoy Roadster
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With a 26" tall tire and 3.73 gears you'll turn 2362rpm at 70mph in OD, which is a little bit high for my taste, but may be OK if you're using it for towing. Going up to a 3.55 only drops you to 2250. Those short tires really boost the rpm's. With the 3.06 to 1 first gear I wouldn't think that towing would be a big problem, provided you have the HP & torque you need.
You can play with the numbers:
Cruise RPM = (mph x Gear Ratio x 336 x OD Ratio)/Tire Diameter in inches
This lets you manipulate the formula to solve for what you want. For example, knowing that your OD ratio is 0.70 in the 700r4 you can simplify to:
Cruise RPM = (mph x Gear Ratio x 235.2)/Tire Diameter in inches, and then if you want to solve for speed at a certain RPM it's simply:
MPH = (RPM x Tire Diameter)/(Gear Ratio x 235.2)Last edited by rspears; 05-16-2015 at 07:19 AM.
Roger
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