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Old 10-05-2002, 01:57 AM   #1
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Default Rollout Figures For Gearing Calculations

Hi,
Recently i was given a Formula for working out the rollout distance for my car to enable me to set the gearing properly for my motor. I was told that for a 9 turn motor the rollout figure should be about 25mm.

This is the formula that i was given.
(Spur Gear divided by pinion size) x Internal Ratio =X

Tire diameter x 3.14 = Y

Y divided by X = Rollout.

So for instance if your spur size was 43 and your pinion size was 14 and your internal ratio was 2.77 you would end up with 8.5 as "X".
If your tire diameter was 65mm then "Y" would be 204.1.
Your rollout figure would therefore be 24.01mm.

What i would like to know is, Does anyone else use this formula??? Can it be relied on as an accurate guage?? and if so where do i get the rollout figures for other motor sizes???
Thanks
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Old 10-05-2002, 03:12 AM   #2
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I use this formula religiously to calculate my gearing. Specially since I run foam tires. The only thing I do different is I calculate my tire size using inches not mm. Very accurate and very reliable way to gear your motors. Once you find the right gearing for the right tracks and motors you can replicate it every time.
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Old 10-05-2002, 04:02 AM   #3
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Thanks sigearhead...
Where can i find more info or a chart to show me rollout measurements for other motor sizes???
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Old 10-05-2002, 08:04 AM   #4
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Would the wind of the motor matter for the calculation? Maybe it corresponds to a particular rollout, humm. I've never messed around with any calculations like that, new to the touring cars and I knew what to run offroad just because I'd been doing it so long.
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Old 10-05-2002, 05:04 PM   #5
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Apparently there are different recommended rollouts for different winds of motors but thats as far as i have got. I asked the guy who initially gave me the formula if he could tell me where to find more info on the subject but he was very vague. I have tried to track something down on the net but came up empty.
I am sure that someone here will know where to find the info..
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Old 10-05-2002, 07:24 PM   #6
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heres a list fro mthe mod motor forum,of roll out figures for all mod winds as well as 27 turn stock...

ROAR Stock 30.99 to 34.38
17 turn 31.08 to 31.86
16 turn 29.47 to 30.30
15 turn 27.86 to 28.68
14 turn 27.08
13 turn 26.28
12 turn 25.53
11 turn 24.69
10 turn 23.88
9 turn 23.10
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Old 10-05-2002, 07:38 PM   #7
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SPAZ456,
you are a legend and far exceed the expectations that your user name suggests
But seriously, thanks for the info. I was sure that it was probably posted somewhere in the vast data bank that is rctech.net but was not sure where to find it....
One other question. What car variances would affect this formula? obviously some cars have very smooth and efficient drivetrains while others not so efficient... How does this affect the rollout figures if at all???
For Example, would the figures apply as well to a TRF414MII as they would to a TA03 DJ Special???
Your opinion would be valued...

Steevo
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Old 10-06-2002, 03:10 AM   #8
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What Spaz456 has posted is a good starting point, HOWEVER gearing has a lot to do with the size and layout of the track that you will be racing in. You have to play with the figures adn check your laptimes, once you have figured out which rollout works best you either remember it or right it down so you can duplicate it in the next race. If you ever look at setups sheets no one uses the same gearing for every car and every motor, you gear based on motor and track size and layout. All the charts you see posted or on kit manuals are starting points.
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Old 10-06-2002, 07:03 AM   #9
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also the wind of your motor has an effect, i.e. 10 turn triple will rev higher than a than a 10 turn single would so you may want to decrease your roll out to around the 9 turn range, that is the way it was explained to me.
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Old 10-06-2002, 08:50 AM   #10
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A triple will rev higher than a single? Isnt it the other way around, the higher winds providing more low end grunt?
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Old 10-06-2002, 04:00 PM   #11
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the triple should have more top end and the single should have more torque. For example, you would run the 10 single in your sedan and the 10 triple would be better suited for 12scale.
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Old 10-06-2002, 04:51 PM   #12
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Yes I agree with spaz456 and sigearhead that single winds have more torque and multiple winds have more top end speed.
In regards to the rollout figures i would assume from the info I have been given that for a tight track the rollout figure should be slightly more and for a fast track with long straights the rollout figure should be slightly less than the benchmark figure for the motor you are running.......
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Old 10-06-2002, 06:08 PM   #13
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nah, rollout is a mesurement of mm per rev, so the higher the number is the 'harder' or taller the motor is geared.

so with the same motor 35mm rollout will have more topend speed, but less acceleration than 30mm rollout, etc.
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Old 10-07-2002, 01:29 AM   #14
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tones: you are right. On a bigger track you will run a higher rollout and on a smaller tighter track you will gear down and run a lower rollout.
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Old 10-07-2002, 03:35 AM   #15
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Ok given all the above heres the current figures for my TA03F running the standard gears and a 9 Turn Trinity.
Spur size=43 Tooth
Pinion size=14 Tooth
Internal Ratio= 2.77
Tire Diameter=64mm
Given all the above my Rollout figure is 23.63mm. The track I usually run on is fairly fast with sweeping corners. Should this in theory be a good ratio to work with???
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