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how to calculate rollout

how to calculate rollout

Old 10-12-2004, 06:56 AM
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hi guys

Can anyone please help me on calculating roll out.

Thank you
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Old 10-12-2004, 07:00 AM
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i needed help on this one too. But this is what i got outta the forums.


RBLove wrote on Today 04:52 PM:
Yeah No problem.

19turn actually take a bigger gear than stock. Tire size has everything to do with it. I assume this person is running on carpet?

Tire size x pie (3.14) = ______
Spur / pinion x internal gear ratio = ______

Divide the top number over the bottom and you have roll out. Do not flip these two when dividing..

Example: X-Ray FK with 2.25 in tires ( I do not use mm).

2.25 x 3.14 = 7.06
132sp / 35pin x 1.77 internal = 6.67

7.06 / 6.67 = 1.058 roll out

Depending on track size, but like Cleveland or Snowbords a monster stock would be geared around a 1.00 or little lower. 19t would be at a 1.12 or even higher.

Hope this helps......
Rob
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Old 10-12-2004, 08:14 AM
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Another way of crunching the numbers is:

(Tire size * pinion * pi) / (spur * internal ratio)

This requires division only once. It is also easy to pull out part of the formula and call it a constant to remove all need for division at the track.

(pinion * tire size) * (pi/(spur*internal ratio))

pinion and tire size are the only 2 things likeley to change so you can pre-calculate the right half.

Using the example numbers above you would just do

pinion * tire size * .0134

The easiest though is to just make a table, but real geeks do it by hand.
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Old 10-12-2004, 08:20 AM
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www.gearchart.com

Click on gearchart creator. It has a section for rollout
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Old 10-12-2004, 08:31 AM
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Default rollout

The question I have is....How do you know what the rollout should be for a particular track?
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Old 10-12-2004, 10:51 AM
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Default roll out

The best site i have ever used and found for roll outs is http://www.arroyoc.com/index.cfm?fus...utilities.gear you can print them out and take them to the track with you so you will always be able to check, like me
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Old 10-12-2004, 12:43 PM
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you don't really know what is the best rollout until you get your car out on the track. Rollout is jjust a useful measurement for holding a setup or trying to copy someone elses. So the best way to find out a good rollout is to ask someone good at the track what they are running.
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Old 10-12-2004, 01:20 PM
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if you're figuring rollout for a pan car, there's no internal ratio needed, it's simply:

pinion x tire size x 3.14 / spur = rollout


if someone has given you a good rollout and you want to figure out what pinion to use, just figure it backwards:

rollout x spur / 3.14 / tire = pinion


jw
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Old 10-12-2004, 02:12 PM
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So heres the roll out of my car ...

(66 x 3.142) (95 24 x 1.81) = 28.96 mm per rev.
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Old 10-12-2004, 02:50 PM
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heres a easy one. roll out calculator
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