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Old 12-27-2010, 12:44 AM   #1
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Default Gearing/ Rollout Question

Alright guys after reading everything i can find on gearing and rollout to get my F1 and Pan cars keeping up with the big dogs I have thoroughly confused myself. Im hoping you guys can set my mind straight.

Here is my question......

If I have 2 cars with the following setups:

Trans Ratio 1.0
Spur Gear: 88
Pinion: 46
Tire Diameter: 55mm
Rollout: 90.32

Trans Ratio: 1.0
Spur Gear: 82
Pinion: 43
Tire Dameter: 55mm
Rollout: 90.61

These cars have essentially the same rollout and the same spur to pinion ratio (1.91) but with different pinion/spur combos. One has less weight due to the smaller gear size but other than that is there any performance difference between the bigger or smaller gears if the ratio and rollout are the same.

Most the racers at the track running WGT run very large pinions and spurs when you could run much smaller gears and achieve the same ratios and rollouts. It has perplexed me. Any insight would be apprecated
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Old 12-27-2010, 03:58 AM   #2
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well I dont know what your trying to ask lol...

But if you wanted a taller rollout u could make the spur smaller and then in turn make the pinion smaller as that would give the same rollout yes... But maybe some of the gear ratios they want to acheive they may not have the spurs and pinions to come up with what they want.. So they are just dealing with what they have...

Its a mith about less weight and rolling mass but the spurs and pinions now days are that light and made so precise you dont have to worry about it. But the other thing was have a look at their cars and take notice of the amount of motor plate movement as they might be only able to get the ratio they are running by using the big pinions and spurs as the smaller gears may not reach... Just some ideas for you mate.
Hope this helps
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Old 12-27-2010, 07:25 AM   #3
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The motor is the single heaviest thing on the chassis. Larger spur / pinion moves this weight forward. More steering less rear bite ??
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Old 12-27-2010, 07:48 AM   #4
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The larger spur and pinion combo will give better low end acceleration

For the same rollout you have a 6 tooth reduction in spur for a 3 tooth reduction in pinion of the 82/43 combo. Theres a greater moment arm/easier for the motor to work the 88/46 combo.

It's like undoing a bolt, the torque is the same whether you do it with your fingers or a wrench, much easier with a wrench. Longer arm, less force vs shorter arm, more force.

Gears also mesh better = more efficient the larger they are.

Last edited by rc_square24; 12-27-2010 at 09:17 AM.
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Old 12-27-2010, 10:08 AM   #5
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Quote:
Originally Posted by rc_square24 View Post
The larger spur and pinion combo will give better low end acceleration

For the same rollout you have a 6 tooth reduction in spur for a 3 tooth reduction in pinion of the 82/43 combo. Theres a greater moment arm/easier for the motor to work the 88/46 combo.

It's like undoing a bolt, the torque is the same whether you do it with your fingers or a wrench, much easier with a wrench. Longer arm, less force vs shorter arm, more force.

Gears also mesh better = more efficient the larger they are.

Now that makes more sense. So to ease the load on the motor and achieve more torque and possibly lower temps with the same rollout I can run a larger gear combo with the same rollout.
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