Understanding Pinion gears

[shozz]

Hi i would like to know what changing your pinion gear tooth number does? I know that it changes you end ratio but in what way? What happens if you use a smaller one ? What happens if you use a larger one ? Thanks a bunch

[TWINSET]

Lower tooth count lowers top speed whereas a higher tooth count increases it.

There are trade-offs though, whether they're noticeable or not depends on the amount of change;

Lower tooth count

-slower top speed

+Faster acceleration to top speed

+Longer run times

+Higher torque

+Cooler running (Motor, ESC etc)

Higher tooth count

+Faster top speed

-Slower acceleration to top speed

-Shorter run times

-Less torque

-Hotter running

[Nobbi1977]

On race bikes we sometimes run lower gearing and get a higher top speed because it allows the motor to rev out before it runs out of puff. Anyone found a car / motor combination that was faster on a smaller pinion?

[WillyChang]

Anyone found a car / motor combination that was faster on a smaller pinion?

Define "faster"... around a racetrack or straight line speed?

Small track with an RC that's only got 1 fixed gear ratio, you may get better lap times on a lower ratio due to better acceleration infield vs what you lose from lower max speed down the straight.

A slight anomaly to fuel engines... sometimes an electric motor might accelerate faster with a heavier-mass pinion.

[Fried Tyres]

A slight anomaly to fuel engines... sometimes an electric motor might accelerate faster with a heavier-mass pinion.

I did not know this. Do you know why this happens?

Chris.

[WillyChang]

I did not know this. Do you know why this happens?

No idea, I ain't boffin like Bill Nye the Science Guy... but have seen serious racers bring pinions of different mass (steel, bronze etc) for each size &/or if there's a cavity cut in they'd fill up with solder etc.

Possibly something to do with electric motors can produce 100% of their torque from 0 RPM but you need something to provide resistance for that torque to be produced; a free revving unconnected motor technically produces zero torque (ignoring mass of armature and friction in bushings). Pinion with more mass gives more torsional resistance to get it spinning... heck who knows, there's plenty of Black Arts back in brushed motor & nicad era

[Wooders28]

Like a few have said:-

Big pinion = Slow acceleration / high top speed.

Small pinion = fast acceleration / lower top speed.

This is a general statement.If you goto extremes, ie put a HUGE pinion on,the motor just wouldn't have the power to drive it upto the top speed,which is why in some cases it goes quicker with a smaller pinion (as with nobbi1977 race bike).

If you have a bicycle,it's like setting off in top gear.Technically you can go the fastest in that gear, but more likely you will (if it was me anyway!) run out of puff before you reach top speed.

Don't get confused looking at the rear wheel gear,that's the ' counter gear' the 'pinion' is where the pedals are.

Which surface you are on has a factor too, on tarmac you can run taller gears as there is less drag on the car than say,grass.

If you are planning on racing,you will need a selection of pinions, for different track layouts.Large pinion for an oval layout with long straights and small pinions for when it's more like a supercross track.

[Backlash]

I did not know this. Do you know why this happens?

Chris.

In simple terms..

With DC electric motors, torque is proportional to the current flowing through the armature, so the more load on the motor, the higher the current drawn by the motor, the more torque is produced.. Typically DC electric motors produce more torque at lower RPM's, and less torque when at their maximum RPM..

Engines (as in nitro/petrol/diesel) produce maximum torque higher up in their rev range..