rcburner

When it comes to the spur gear and pinion gear. What configuration will boost top speed? What configuration will increase acceleration?

jbrow1

iTrader: (28)

Bigger pinion = more top speed.
Smaller spur gear= more top speed.

Smaller pinion = more low end punch.
Bigger spur gear = more low end punch.

I believe changing one tooth on the pinion is equal to changing four teeth on the spur. Meaning if you change the pinion it's a more dramatic effect than the spur. At least that's how it is on my GT. Not sure what pitch gears you are working with.

DrOlds

iTrader: (4)

Actually it's the other way around-4 teeth on the spur is about the same as 1 tooth on the pinion.On electrics we are usually using spur gears around 80-90 teeth and pinions some where around 20.

Here's the basic formulas to calculate gearing-

spur / pinion = external ratio example-88/22=4 or 4:1 ratio
external ratio X transmission(or internal)ratio=overall ratio
example- 4 x 2.4(B3 transmission)=9.6 or 9.6:1

tire diameter x pi(3.14)=circumference of tire 3"x3.14=9.42" of travel per tire revolution

tire circumference / overall ratio = rollout(distance traveled per motor revolution)

Example- 9.42"/9.6 ratio=.98125" rollout
or 235mm/9.6 ratio=24.5mm rollout

It is more common for rollout to be given in mm. but the formula is the same.

jbrow1

iTrader: (28)

And that's just what I said, one tooth on the pinion is like changing 4 teeth on the spur.

DrOlds

iTrader: (4)

Yes it is! Sorry

jbrow1

iTrader: (28)

RC Burner, the forumula he posted above is used in onroad racing with foam tires. Our tires (offroad) are basically all the same size and don't vary that much. So just the pinion size and spur size is what offroaders worry about.

I just got into carpet racing last winter, so it was informative for me. Thanks!

rcburner

thanks guys! good info!

howerc

iTrader: (6)

do you increase/decrease the spur to improve run time?

Team Duratrax

Bigger spur gear and a smaller pinion gear will increase runtime slightly.

Sean

howerc

iTrader: (6)

thanks for the help

Platinum_Racing

What ever you do be carefull not to overgear or undergear your motor. This could lead to severe motor damage, including killing it forever, Its not just your gear ratios that matter, its the size of your tires, they play a major role in how you should gear your car.

rcburner

Could you elaborate more on the issue of the tire size?

Platinum_Racing

Your tires also determine how you should gear your car. a tire that is 2.2 inches in diameter will travel further in one rotation than a tire that is 1.8 inches in diameter. There is a sweet spot for every track, every car, basically every situation. If you run wide open all the time, you can get away with faster gear ratios, but if your constantly accelerating, you should gear it lower, this will lower the motor temp, make your batteries last longer, and make your car perform better. If you swap tires to ones that are slightly larger, drop between 1 - 3 teeth on your pinion to compensate.

rcburner

When you say faster gear ratio, do you mean increasing the pinion to get more top speed or decreasing it to gain more accelaration?

Platinum_Racing

I'm sorry, I meant to say higher gear ratios. Yes, install a larger pinion or a smaller spur.