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Old 10-05-2008, 05:21 PM   #1
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Default selecting a pinion

Hello everyone I recently bought a 12r5 by associated, i am running a novak esc and a 27 turn monster stock motor. I have brand new jaco tires, i was wondering how i select the pinion i should start off with
I know the gear is 64 pitch 94 tooth on the axle, i just need something to start from ?? any help is greatly appreciated
Thanks everyone
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Old 10-05-2008, 05:51 PM   #2
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You'll need to let us know the tire size and the size of the track you're running on. Also if the layout is open and flowing or tight and technical.
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Old 10-05-2008, 05:54 PM   #3
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With the info you have given me. I would say 25-40 tooth. More info is needed like Trips said.
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Old 10-05-2008, 06:13 PM   #4
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ok so the trakc is carpet indoors, i would say it isnt overly large and flowy, but then again it isnt tight, i would say it is in the middle, a little more on the tighter side. as for tires, i have not done anything to them but mount them so they are the stock size, which im not sure what that is
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Old 10-05-2008, 09:37 PM   #5
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Quote:
Originally Posted by shipwama View Post
ok so the trakc is carpet indoors, i would say it isnt overly large and flowy, but then again it isnt tight, i would say it is in the middle, a little more on the tighter side. as for tires, i have not done anything to them but mount them so they are the stock size, which im not sure what that is
Okay, not looking to frustrate you and I'm not trying to give you a hard time, but if you can't measure the diameter of your tires it's impossible to give you a suggestion on gearing.

All you're telling us is that they're out of the box Jaco tires,that doesn't help much... I've had two sets of jacos (same rim, same compound) come out of the box different enough in diameter to need different gearing. Add to that the fact that Jaco has made and sold tires on several different rims, and we're simply unable to guess at what you have on the car.

If this is any help, I'll give you the formula for determining rollout. Rollout is the distance your car will move forward for each revolution of the motor.

To calculate rollout, you first multiply the rear tire diameter by 3.14 to get the circumference. That's the distance the car will move forward for one revolution of the tire. Now to determinie how far the car will move for one revolution of the motor, you divide the pinion by the spur, and multiply THAT result by the circumference of the tire... for example, if your tire is 1.8" in diameter, and you're running a 30 tooth pinion with your 94 spur, you'd multiply 1.8 x 3.14 to get 5.652 (that's your tire circumference) now divide your piniono by your spur, 30 / 94 to get .319. Now multiply 5.63 by .319 to get a rollout of 1.79 inches.

That's fine, but you don't need to find your rollout, you need to figure what pinion to run... to calculate that, first you need to know what a good rollout is to be running. For a 1/12 car ono a medium size carpet track, I'd be thinking somewhere around 1.65 to 1.7 inch for a monster stock motor like you're running. To get the pinion, you multiply the spur by the rollout you're trying to get (in your case, a 94 spur and 1.65 rollout) to get 155.1 Now, divide that by your tire's circumference (for example, let's say your tire is 1.8 inch in diameter like the last example) Multiply 1.8 by 3.14, you get 5.652, then divide 155.1 by 5.652 to get 27.44 since you can't get a 27.44 pinion, you'll want to run either a 27 or a 28.

Of course, you'll need to measure your tire diameter, unless they're 1.8 inch like in this example, these numbers won't be appropriate for you.

Hope that helps...
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Old 10-06-2008, 10:06 AM   #6
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Thank you very much your help is greatly appreciated, i have never ran anything onroad before, just offroad, so i have never had to deal with this, thanks for bieng patient and laying that all out for me
Matt
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Old 10-06-2008, 10:21 AM   #7
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I find that gearing by temperature is the most accurate way of finding the best final drive ratio. You want to approximitely hit 160-170F in motor temperature.

No math required...
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Old 10-06-2008, 10:57 AM   #8
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Matt,

No problem, I'm glad I could help. If you're wondering where the 1.65 suggested rollout for your mkonster stock comes from, it's just from personal experience... My monsters seemed pretty happy right around there. For the blue CO27 motors, they seemed to be happier around 1.72 or so, and the ReedY Stockstar motor did pretty well for me at 1.8

Foxxricket's advice about temperature is good... If you're getting above 160-170 you should drop a tooth or two on the pinion. If you're coming off much cooler after a run, you might want to go up a tooth or so, but always look at lap times... depending on the layout, you might get your best lap times geared shorter than what would get your motor up to 160.

Rollout is great to be able to keep your gearing consistent as your tires wear down in size... Once you've found your best lap times for a particular motor and layout, and the motor isn't getting too hot, calculate the rollout, and make a note of it. then as your tires wear down, check the math and see when you'll want to go up on the pinion to maintain the same rollout that was working well.

Have fun...
D
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