hi guys

Can anyone please help me on calculating roll out.

Thank you

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

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.

www.gearchart.com

Click on gearchart creator. It has a section for rollout

The question I have is....How do you know what the rollout should be for a particular track?

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

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.

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

So heres the roll out of my car ...

(66 x 3.142) ÷ (95 ÷ 24 x 1.81) = 28.96 mm per rev.

heres a easy one. roll out calculator