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Old 01-21-2005, 05:46 AM   #1
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What are the equations for roll-out, final-drive, and any other important ones related to touring car racing, thanks.
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Old 01-21-2005, 06:18 AM   #2
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Final drive:

(Spur/pinion)*internal ratio

Internal ratio: Diff Teeth/pinion pully teeth


(Pi*D)/ Final Drive Ratio

D=diameter of tires
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Old 01-21-2005, 06:31 AM   #3
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On a direct drive car (like a 12th scale) use the following:

MMPR (MilliMeters Per Revolution, It's how far the car will travel in mm when the motor makes one revolution)

W= Wheel diameter in mm

S= Spur gear teeth (ex: 96T spur)

P= Pinion teeth (ex: 25T pinion)

MMPR= (P/S)*(3.1416*W)

Example: My 12th scale has a monster Pro and 39 MMPR is a good rollout for that motor. What Pinion do I use??
I measure, W=46mm, My spur is 96.

Round it off to P=26T

So slap in a 26T pinion and it's go time!!

For cars with internal drive ratios (Like a TC3, it has an internal drive ration of 2.5:1) Check your user manual for the drive ratio and add it to the above equation like so:

DR=Drive ratio (Ex: DR=2.5 for a TC3)

MMPR= (1/DR)*(P/S)*(3.1416*W)

Example: I'm running a 19T spec motor in my TC3, what pinion do I use. Guys at the track say that 25 MMPR is a good start.
I measue, W=65mm (full size TC tire), My spur is 100T

Round it off to 30T or 31T

Select the 30T or the 31T and try it out.

This equation can be applied to any car, a AE B4 has a 2.6:1 drive ratio so just apply it as above.

Hope this helps.
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Old 01-21-2005, 02:55 PM   #4
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Thanks guys, are there any other important ones relating to touring?
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Old 01-21-2005, 07:04 PM   #5
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I've put a makeshift Excel based Calculator on my website.


The rollout Calc is linked at the bottom.

There is an area to put in:
Tranny Ratio
Tire Diameter

Just leave the one you are trying to calculate Blank... enter the others and it will give you what you need.

ie.. if you want a certain rollout but need to know what pinion to use you just enter all of the info but the pinion and it will tell you which pinion to use.

Some guys with Mozilla have said they had trouble with the calc... it is based on Microshaft software so who knows... though i would imagine there is a plug-in for such. Anyway... I'm working on a couple others that aren't dependent on Microsofts Internet Exploiter! lol May never come to fruition though... I barely know jack about this web stuff! lol
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Old 01-21-2005, 07:13 PM   #6
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That is whay I am doing for myself, I created a VB program and just making sure I have everything I need.
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