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Calculate Rollout

Calculate Rollout

Old 11-28-2004, 09:35 PM
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Default Calculate Rollout

I'm used to running on asphault with rubber tires so rollout is not a factor. Now I'm racing on carpet and need to calculate rollout. I checked all the other rollout threads and they just give the websites to get charts. I don't need charts. Any person can punch numbers into a program to come up with a chart. I want to know the mathmatical formula to come up with those numbers. I am also looking for an average rollout for a tuned stock motor on a small technical track. BTW I use mm in measuring the tire diameter.

Thanks in advance.
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Old 11-28-2004, 09:51 PM
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Tire size times PIE (3.14) divided by spur times pinion.
Ie. 1.74*3.14=5.4636 / 98 = .05576 (rounded) * 38 = roll out of 2.11

There are other ways, but that is how I do it.
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Old 11-28-2004, 09:53 PM
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Thanks Smalls.

That seems to sound right.
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Old 11-28-2004, 10:22 PM
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is your figure for sire size in inches, centermeters, millimeters???

Also, does the diametric pitch of the gears affect it at all??
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Old 11-29-2004, 07:28 AM
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What kind of PIE do you use in your rollout?

pecan? apple, cherry? or pumpkin?



Originally posted by Smalls
Tire size times PIE (3.14) divided by spur times pinion.
Ie. 1.74*3.14=5.4636 / 98 = .05576 (rounded) * 38 = roll out of 2.11

There are other ways, but that is how I do it.
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Old 11-29-2004, 10:51 AM
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If you are running a TC you also need the internal ratio in the formula. I use tire diameter*PI*pinion/spur/internal ratio

I like pumpkin pie!!
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Old 11-29-2004, 10:54 AM
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Default gearchart.com

Here is a great site done by a buddy!

http://www.gearchart.com/
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Old 11-29-2004, 12:12 PM
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Default Re: gearchart.com

Originally posted by E.J. Evans
Here is a great site done by a buddy!

http://www.gearchart.com/
Thanks newracer. I was wondering why the formula that was previously mentioned was also on a 1/12th forum and the numbers I was coming up with didn't seem right.

E.J.- I was looking for the accual formula to calculate rollout so I would have the knowledge to make changes to compensate for a change. Not to have a bunch of charts that mean squat.
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Old 12-04-2004, 08:34 AM
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Default Re: Calculate Rollout

Originally posted by NismoSkyline17
I'm used to running on asphault with rubber tires so rollout is not a factor. Now I'm racing on carpet and need to calculate rollout. I checked all the other rollout threads and they just give the websites to get charts. I don't need charts. Any person can punch numbers into a program to come up with a chart. I want to know the mathmatical formula to come up with those numbers. I am also looking for an average rollout for a tuned stock motor on a small technical track. BTW I use mm in measuring the tire diameter.

Thanks in advance.


I gave you the 12th scale roll out. You never said it was for TC ( although I assumed it when I saw rubber tires ), but you never said what it was for and what your drive ratio was...
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Old 12-04-2004, 10:07 AM
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Default Re: Re: gearchart.com

Originally posted by NismoSkyline17
Thanks newracer. I was wondering why the formula that was previously mentioned was also on a 1/12th forum and the numbers I was coming up with didn't seem right.

E.J.- I was looking for the accual formula to calculate rollout so I would have the knowledge to make changes to compensate for a change. Not to have a bunch of charts that mean squat.
You only need one chart, (for each type of car) as your foams wear down, it will tell you what pinion to use.
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