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Old 05-31-2011, 10:26 PM   #1
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Questions?? Sprint 2 gearing?

I just picked up a used sprint 2 with a 17.5 novak system in it....the guy bought it and went to one race and ran one qualifier and decided it wasnt for him....he said the guys at the LHS geared it for him, they said they had to to meet the rules of the local track....the car must be "stock brushed or an equivelant 17.5 brushless" with a set final gear ratio of 4.5...which means nothing to me...sorry I'm an onroad newbie

I got it and it looked like it was geared WAY too high...I test drove it and after 3 minutes of mild driving the motor was at 165* and the ESC with a fan was at 170*...this was on a 50* degree day...

He had a 41t pinion and 70t spur....I have never had an onroad car before but that seemed WAY too high and the motor and ESC temps seemed to confirm my concerns.

I found a 87 tooth spur in the box of stuff that came with the car and put on a 21t pinion I had laying around now after 5 minutes of normal to aggressive driving the motor was 105*...the car seems a little slow but I am not running any timing or boost.

My question is that the original gearing just seemed way off to me....could the local track really require that type of gearing??
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Old 06-01-2011, 05:10 AM   #2
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The final drive ratio (FDR) refers to how many revolutions of the motor it takes to turn the wheels one revolution.

The Sprint 2 has a 2.13 transmission ratio.

So then With a 41t pinion and 70t spur you would have an FDR of 3.64

When you switched to a 21t pinion and 87t spur you now have an 8.82 FDR

This would explain why it seems so slow with this setup.

If you put in the 87t spur with the 41t pinion, you'll have a 4.52 ratio.
This should put you right where you want to be if the track is limiting the class to 4.5
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Old 06-01-2011, 09:06 AM   #3
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kwkride......Thanks for the reply!

That makes sense, I talked to the LHS and they said the old rule was a 3.5 and after some issues they changed it to 4.5

I am guessing a few guys were running too hot and had some issues....this is a new class they only race 1/8 GT until a few weeks ago
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Old 06-01-2011, 01:05 PM   #4
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You're welcome, I'm glad it helped.
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