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Old 02-26-2008, 03:56 PM   #1
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Default Gear Ratios/ Spur Gear

Hi there

I understand gear ratios and use the www.gearchart.com to calculate my final gear ratio's.

When I use the calculator for say my TC4 with 72spur and 22 pinion it gives me a ratio of 8.18. If i use say a 98spur and 30 pinion I get a ratio of 8.17.

Obviously you get a slightly different gear ratio which could affect
performance. But what other reasons would there be to change say the spur gear as oppossed to just the pinion.....

Thanks

Dwayne
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Old 02-26-2008, 06:09 PM   #2
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One reason would be the location of the motor, and whether the combo will fit with the motor adjustment slots available. Your two examples end up with significantly different motor positions.

Generally in my off road rides I try to keep to the small side on both gears that give the ratio I want and will fit. The motor is then farther forward, farther away from rear guard, thus better protected. The weight/mass of the motor is closer to the center of gravity, which will make the car turn slightly easier. And the smaller pinion will accelerate slightly easier. Not claiming huge differences here, but why not take what ya can?
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Old 02-26-2008, 09:03 PM   #3
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Quote:
Originally Posted by Sparky7B View Post
Hi there

I understand gear ratios and use the www.gearchart.com to calculate my final gear ratio's.

When I use the calculator for say my TC4 with 72spur and 22 pinion it gives me a ratio of 8.18. If i use say a 98spur and 30 pinion I get a ratio of 8.17.

Obviously you get a slightly different gear ratio which could affect
performance. But what other reasons would there be to change say the spur gear as oppossed to just the pinion.....

Thanks

Dwayne
if you calculated 98spur30 pinion and 72/22 to be that close its the same ratio.its a .006 difference spur/pinion ratio(are you talking about wheel to shaft as the final?)Rule of thumb is if you want that ratio, go with the smallest of the 2 possible.Less rotating mass and in alot of rear end motor mounted cars the motor will be closer toward the middle and can make a slight handling differnce as Dave H has pointed out.

But these are very slight in difference and for example,if you are at the track and need to gear the car a certine ratio and you have not the smallest gears possible but have the gears to make the ratio needed,,i wouldn`t go out of the way to get the smallest ones because it wouldnt be worth it.

But if you have an entire strip of pinions and spurs, bust out the calculator and start grabbing for the smallest ones that pop up in the ratio you are looking for.

If you find a ratio that you like the best for a certine track.The next time you go there,show up with the smallest gears possible that makes the same ratio.

Even though it is a slight difference,alot of slight differences add up.Pennies can add up to millions of $ and thats how the pros look at it when it comes to racing.Every difference counts.
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