Help with gearing please

[Paulstar]

Hi Guys.

Right i've got my car set up and its seems to be ok. I've started to look at my gearing extra. At the moment i have a 21t pinion in there.

Looking on the net at gears and pinions there is loads of numbers that i dont know what they mean

Sorry to be such a novice. Could someone give me a rough guide.

What is 48dp or 64dp??
Also changing the spur gear. What difference would this make to the car??
And the same with the pinion?

Sorry again to be such a novice lol

Thanks in advance.

Paul

[RogerM]

Haven't got much time now but will try to answer in full later if somebody doesn't beat me to it.

For the Kyosho cars you need 48dp pitch gears (the most common).

If you give us an idea of the motor and description of the track somebody will be able to help with a starting gearing which will at least be a safe place to start from.

[Fabs]

64DP AND 48DP are different pitches for the pinions and spurs (same as module in metric). To put it simply, it defines how big the teeth are on the gears.

For Off Road we only use 48DP as 64DP are way too fragile, on road cars use either with a preference on 64DP for a smoother and less noisy drivetrain (as well as more sensitive gearing adjustments).

Depending on how many teeth on your spur gear and pinion, as well as the internal ratio (which is car dependant) you can calculate the overall gear ratio with the following formula

ratio = (spur/pinion) * internal ratio

The internal ratio on the ZX5 is 2.5, on the RB5 it's 2.6

As an example the ratio on a ZX5 with a 78 spur and 17 pinion is 11.47.

Now a smaller number will give you more top speed but less punch, and vice versa.

Smaller pinion = higher number = less top speed
Bigger pinion = smaller number = more top speed

For spur gears, it works the opposite. However in buggies we tend to pretty much stick to one or two spur gear sizes and change only the pinion (main reason being that pinion is much easier to change, another one is you lose your slipper setting when you change spur gear).

Overgearing is when you have a gear ratio that is way too small for the motor, and results in losses in top speed as well as punch, and ultimately can lead to overheating and possible damage.

Undergearing is the opposite, but results in a lot of punch and little top speed. Not as bad as overgearing but can still lead to overheating.

As a rule of thumb a good gearing is usually achieved when the car reaches its top speed bout 3/4 down the straight. There are also factors like the ability to take the jumps properly that can lead to wanting to change the gearing in order not to achieve top speed but better punch for the jumps.

Anyway I think I've got it all covered now.

Anymore questions let us know.

[Paulstar]

Thats Brillant. Cheers for that.

I've got the ZX5 KMC. Which I know is not the best by the comments on here. But i had a good deal on it and is all i can afford for the moment so i'm just having fun with it. Would the ratio by the same as the normal zx-5, So a 2.5?

[RogerM]

Internal ratio is the same yes.

What motor / battery combination you running? Let us know and we'll try to give you a good starting point

[Paulstar]

Im running a 19t motor with 3900 cells at the min. I've got a 21t pinion in there at the moment. But i'm not sure what spur gear. I'm guessing it was the one that came with the kit

cheers

[998R]

How do I know is the right gearing for different turn motor? Is there a chart to follow?

[SimonW]

Try a 24t pinion to start, that should be slightly under geared for a 19t. As a rule i tend to run 6-7 teeth higher than the motor turns ie: 10t = 16/17 tooth and 19t = 25/26 tooth.

HTH SimonW

[sosidge]

Originally Posted by SimonW

Try a 24t pinion to start, that should be slightly under geared for a 19t. As a rule i tend to run 6-7 teeth higher than the motor turns ie: 10t = 16/17 tooth and 19t = 25/26 tooth.

HTH SimonW

I've run 19T spec a few times in 4wd and they prefer to be geared more like a 13 or 14. So I would be looking at a 19 or 20 tooth pinion. Gearing at 24 would probably cook the motor pretty fast.