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If you know that a certain rollout works for a track with a certain run line length, is the rollout directly proportional to the runline? (Flat track)



For instance, if you know that a rollout of 2.28 is good for a 208 ft run line, would a rollout of 1.53 be good for a 140 ft run line?



208 / 2.28 = 140 / X

Where X = 1.53

If this is true, does it apply to Stock, 19t and/or mod?

Thanks
 

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It should get you close but it does not account for how the turns are (tight or sweeping), rolling resistence (caps versus foams), banking of the track (flat or banked), weather outside (high temps, you may need to gear down a bit so the motor does not overheat).

The only time I would use that calculation is if both tracks you run on are very similar. Say for instance 2 flat carpet tracks with turns that are about the same dimensions then I could see it working.
 

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race3737 said:
If you know that a certain rollout works for a track with a certain run line length, is the rollout directly proportional to the runline? (Flat track)



For instance, if you know that a rollout of 2.28 is good for a 208 ft run line, would a rollout of 1.53 be good for a 140 ft run line?



208 / 2.28 = 140 / X

Where X = 1.53

If this is true, does it apply to Stock, 19t and/or mod?

Thanks

As the other reply suggests, you can run the same roll,
on tracks that are 30-40 feet different.
If your example is from experience, and you do indeed run that 2.28,
on the big track, then the formula most likely will not work,
as a 1.53 seems to be quite low, for a 140 footer....
depending on a lot of variables, of course, we run around 1.90 on
a track about that size. (carpet)

I think mathematically, the flaw comes from using a direct proportion.
using your formula, if you raced on a track of 100 feet,
you'd need about a 1.1 roll.... that just isn't likely.

The easiest "formula", is asking a guy that seems to get around well,
what range roll does he run! If he's really good, and says 2.02,
you should try something about 2 teeth smaller, as generally he
is really dialed in, and you won't be right off.
He'll be on the throttle a lot more than you, and can utilize the
higher roll. just my opinion of course... good luck.
 

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Flat Carpet Tracks

I agree with Dan. The only way you might be able to use that formula is if the smaller track was proportionaly smaller than the bigger track. Meaning that if the runline is 32% shorter, the straight away's would have to be exactly 32% shorter as well as the turn radius & all the deminsions of the track. Our old track was around 140ft as well & we too ran around a 1.90 R.O. Most smaller tracks are at least 30ft to 36ft wide & a lot of the bigger tracks aren't any more than 48ft wide so that alone shoots your formula down. Your best bet is to ask around when you are at a new track & start from the responses you get. From there you should be able to fine tune according to lap times & the way your motor pulls on the straights.


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Brent Pearcy
Bulit Motorsports
 

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Dave, Erock is right, roll-out does not account for the biggest factor in gearing, and thats how the car handles. Some people, like me, prefer a looser car, which allows me to run a higher roll out than most people. No matter where I go, I always finished at least .07 higher in roll out than most other people. Someone who likes a much tighter car, finds themself normally running a lower roll out because the car is stuck so well to the track it needs more torque. Also, roll out does not account for the varience in each individual motor. Each motor makes the most amount of power at a certain rpm or torque range, and the motor needs to be geared for it's most effecient point. Gearing is hard, after you have ran a few different tracks of different lengths you get a feel for where to start, but it's always a little different no matter where you go.
 

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i used to think run line length , was roll out.... but i dont anymore...

i did alot of traveling last winter to carpet tracks... most of the track had a rollout that made no sense... take out big carpet track.. rolout is roughly 2.30 with a monster stock.. the runline is 205...

now we went to michigan for regionals... the track was about 150... we were rolling at 2.40-2.50..... the track was all around tighter.. not as free flowing ect/.... but we tried running a rollout recomended and were 2-3 laps off the pace... started gearing up, and boom ..... the cars semed to fall of really bad...at the end.. but up front (2-3 minutes) they were alot faster... about a lap a minute faster... so if u ran a roll that finished strong, u have one minute to make up three laps... it was confusing....


i guess with all the rambling my point is....check your lap times..... and ask the fast guys.... the better your car handles will also effect rollout... get the car where u want it... then run a few diff rolouts.. check your times and see which is stronger....
 
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