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Old 05-10-2005, 04:42 PM   #1
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Default roll out

What is the equation to find your roll out?

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Old 05-10-2005, 04:58 PM   #2
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For a 12th scale..

Tire Size x 3.14159 / spur gear x pinion

For a touring car for a TC3/TC4

Tire size x 3.14159 / spur gear x pinion x 2.5
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Old 05-10-2005, 05:16 PM   #3
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The touring car formula is wrong! That only works for a TC3/4 which has an internal ratio of 2.5 Other cars don't have that ratio, change numbers accordingly.
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Old 05-10-2005, 08:03 PM   #4
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Oops, my bad should have mentioned that.
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Old 05-10-2005, 10:05 PM   #5
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Ya but he's running a TC4 so it's all good
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Old 05-11-2005, 06:53 AM   #6
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I'll go you one better Every can calculate roll-out (assuming they know the equation), but ever seen the equation for finding a pinion when someone gives you a roll-out number?? I have...here it is...

To Calculate Roll-Out:

Tire Diameter (in mm) * Pi (3.14159) / (spur/pinion*drive ratio of car)

To Find Pinion Needed:

Roll-Out * Spur * Drive Ratio / Tire Diameter (mm) * Pi
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Old 05-11-2005, 08:57 AM   #7
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or you can use the roll out calculator at www.gearchart.com
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Old 05-11-2005, 10:44 AM   #8
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Quote:
Originally posted by k_bojar
I'll go you one better Every can calculate roll-out (assuming they know the equation), but ever seen the equation for finding a pinion when someone gives you a roll-out number?? I have...here it is...

To Calculate Roll-Out:

Tire Diameter (in mm) * Pi (3.14159) / (spur/pinion*drive ratio of car)

To Find Pinion Needed:

Roll-Out * Spur * Drive Ratio / Tire Diameter (mm) * Pi
wats the * ? is that a multiplication sign or wat man? can u write how you would type it on a calculator! ty
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Old 05-11-2005, 11:21 AM   #9
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* = multiplication

/ = division
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Old 05-11-2005, 11:21 AM   #10
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Default

Quote:
Originally posted by k_bojar
I'll go you one better Every can calculate roll-out (assuming they know the equation), but ever seen the equation for finding a pinion when someone gives you a roll-out number?? I have...here it is...

To Calculate Roll-Out:

Tire Diameter (in mm) * Pi (3.14159) / (spur/pinion*drive ratio of car)

To Find Pinion Needed:

Roll-Out * Spur * Drive Ratio / Tire Diameter (mm) * Pi
to work out the pinion from an FDR would i just do that equation but without the 'roll-out' part?
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Old 05-11-2005, 01:34 PM   #11
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Quote:
Originally posted by raving-monkey
* = multiplication

/ = division
Thanks...
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Old 05-11-2005, 01:38 PM   #12
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Quote:
Originally posted by raving-monkey
to work out the pinion from an FDR would i just do that equation but without the 'roll-out' part?
I guess...Final drive (I thought) is just:

Spur / pinion * drive ratio = FDR

I haven't done much with FDR - most guys over here worry about roll-out instead of FDR

Thinking about it...it should work....
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Old 05-11-2005, 02:00 PM   #13
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Default roll out.......

why is it so important? doesn't it comes down to spurgear & pinion combination I mean unless you adjust your FDR ratio by ripping off material of your tyres!
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Old 05-11-2005, 02:50 PM   #14
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well guys that run foams are changing their 'rollout' all the time because their tyres are wearing.

not so bad for the rubber guys because their tyres stay the same (diameter that is)
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Old 05-11-2005, 03:23 PM   #15
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Default Re: roll out.......

Quote:
Originally posted by Omar R
why is it so important? doesn't it comes down to spurgear & pinion combination I mean unless you adjust your FDR ratio by ripping off material of your tyres!
Roll out is important because, like raving-monkey said, foams tires change their diameter basically every run...and that's before you true them Its not uncommon for a, say, magenta compound foam to lose about 1mm of rubber after a 5 minute run...So by doing the roll-out your car stays the same speed as it was with the larger tires...

it also helps from blowing up motors too too small diameter tires can be just as bad, on a motor, as over gearing it with a pinion and spur combo

Be lucky if you run on rubbers all year long
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