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Old 11-28-2004, 09:35 PM   #1
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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   #2
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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   #3
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Thanks Smalls.

That seems to sound right.
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Old 11-28-2004, 10:22 PM   #4
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Default

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   #5
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What kind of PIE do you use in your rollout?

pecan? apple, cherry? or pumpkin?



Quote:
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   #6
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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   #7
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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   #8
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Default Re: gearchart.com

Quote:
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   #9
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Default Re: Calculate Rollout

Quote:
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   #10
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Default Re: Re: gearchart.com

Quote:
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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