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Old 08-12-2006, 05:01 PM
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Anybody know the rollout formula?Please post.
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Old 08-12-2006, 05:20 PM
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Here it is:

Rollout = Tire Diameter (inches) X 3.142 X Pinion / Spur Gear
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Old 08-12-2006, 05:45 PM
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Rollout = Tire Diameter (inches) X 3.142 X Pinion / Spur Gear X Internal Ratio

For gear box cars I think

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Old 08-12-2006, 09:17 PM
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Default Rollout Calculation

RockDog is right except I think he forgot a parenthesis there. Add a parenthesis around the last two (spur gear x internal ratio). Expressed like you would punch in a calculator, rollout is

Tire Diameter x 3.14 x pinion teeth / spur teeth / drivetrain ratio

Example, 62 mm rubber tires
62 mm x 3.14 x 31 teeth / 78 teeth / 2.5 = 30.9 mm
If you like english units, 30.9mm / (25.4 mm/inch) = 1.217 inches

This happens to be close to the right rollout for our local track for a CO27 stock motor.

I punched in mm tire diameters across a row, pinion sizes down a column on the left, copied the whole block for several spur gear sizes, typed in the formula into excel and copied it all down so I have a gear chart for my race log book. A cell phone calculator or hand math (if you're good) is OK but the chart is faster. People always say go to Gearchart.com to make one that is fine also. I just like my chart because I jam pack it full with all kinds of tire sizes and gear combos (plus I'm a geek I enjoy making stuff like that).
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Old 08-12-2006, 09:40 PM
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Originally Posted by serpentpro28
Anybody know the rollout formula?Please post.
easy way is to go to..............Gearchart .com
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