Gearing Question: Pinion/Spur

[Dudders]

Hi All,

Just thinking about gearing and my head hurts.

Why would you run a larger/smaller spur with a larger/smaller pinion?

What are the advantages and why?

Would a small pinion and small spur produce quicker excelleration and the reverse more top end?

If the above is correct, why use a small pinion on a larger spur?

Neil

[Dave Dodd]

a small pinion and a large spur would produce more acceleration and vice versa for more top end, but generally your never too far from kit std gearing but it all depends on the size of the track your racing on.

if its a small track then they may use a small pinion and large spur as top speed would not be important.

hope this helps, sure someone with more knowledge will put me straight too

[The Chef]

Right where to start. Think about it like your mountain bike, but having met you I'm not sure that you have one. lol

if you have a small gear at the front (pinion)(say 10 teeth) and a Large gear at the back (spur)(10 teeth) then your legs will go round lets say 1/1 so for every revolution your pedals make the rear wheel goes round once o keep it simple. This set up give vast pick up and lots of torque low down but you can't do any mid range r high speed. So lets think about the reverse, you have the biggest cog at the front(pinion)(30 teeth) and the smallest at the rear(spur)(10 teeth) now your rear wheel will do 3 revolutions to every one of your pedals giving a gear ratio of 3/1 which would give you slower acceleration but hiher top end. And there are also points where you can reach the same ratio with different size gears. if you want to keep it simple you can divide the driving gear by the driver to give the gear ratio. If you want to get more complex you will also need to know the other gears in the drive train but it is not often that these are changed and the manufacturer normally states these, so the maths isn't that hard.

Does this help or am i just waffling?

[Dudders]

Waffle but helpfull waffle, enough of the mountain

Understand that but the drive on the car is the pinion so how does that effect?

[Dudders]

So, for arguments sake, I have a 23 pinion and 84 spur.

IF I put a 21 pinion on it will it give more top end or excelleration?

IF I put a 81 spur on will it give more top end or excelleration?

[The Chef]

21 pinion on 84 spur more acceleration less top end ratio of 4/1
23 pinion on 84 spur less acceleration more top end 3.65/1
23 pinion on a 81 spur is in between them both 3.86/1

The more times the pinion has to go round to power the spur the more acceleration you get with less top end.

DOES THAT HELP?

[damselfly]

Originally Posted by The Chef

21 pinion on 84 spur more acceleration less top end ratio of 4/1
23 pinion on 84 spur less acceleration more top end 3.65/1
23 pinion on a 81 spur is in between them both 3.86/1

The more times the pinion has to go round to power the spur the more acceleration you get with less top end.

DOES THAT HELP?

23/81 would have less acceleration than the other two, but it would have a greater top speed.
As you know your onions though I guess it was just a typo.

[ian h]

Also using different size spurs alters your motor position when meshed properly. Eg on a b4 using a 75 spur rather than the kit 81 will move you motor forward towards the axle by a couple of mills therefore changing your overall weight balance. So can be a tuning aid where grip changes from high to low when it rains etc.

[wacattack]

Originally Posted by Dudders

excelleration?

[SlowOne]

A gear ratio is simply that - a ratio. It is generally true that if the ratio is high (2:1) then the car goes faster in a straight line and accelerates slower, and if it is low (4:1) then the car accelerates faster and has a lower top speed given the same motor is in use.

How you get that ratio makes no difference to that generality. You can run 20:80 to get 4:1, or you can run 21:84, or 22:88... However, it does make a difference to efficiency. The larger the spur and pinion you can mesh, the more teeth are in contact, and the lower the rubbing velocity of one tooth over the other. This means that the mesh is 'stronger' and less liable to fail under shock loads, and that the gear train is more efficient. Sounds great, but...

Since we have so much power, and fuel in the tank (battery capacity) we don't much care about efficiency in order to win the race. So, the best reason for using the largest possible combination is to give an extra margin of strength to the gear mesh. If you had the choice above, choose 22:88.

The ratio effect is only a general rule because if you let a motor rev too much it will get hot, and if you are trying to get weight on the move you need torque, not power. Sometimes, you will get more acceleration by using the torque available and run a higher gear ratio, and sometimes you will get more speed if you gear down and let the motor rev. That's why you run higher wind motors (10.5) at higher ratios, because they have more torque, and you can't get the power out of a 5.5 unless you gear it down and let it rev. HTH

[Naushad]

I've learnt something today by reading this topic!