General Gearing Question

[deano261]

Hi i have read a few threads now and jst want someone to explain the numbers realting to gearing . I am looking at buying a brushless motor (6.5t - 9.5t0 and want to know what the numbers people are putting down like 23/80 and how to get a good speed whilst keeping the acceleration highish.

i have only raced at one track where the main straight wasnt very long and was getting demolished midway through it, any help would be much appreciated

[Robbiejuk]

The two numbers that people are putting down are the pinion / spur gear sizes.

In your example 23/80 would be read as having a 23 tooth pinion (Small metal gear attached to motor) and and 80 tooth spur gear (Larger usualy plastic gear mounted on the layshaft for the gear box.)

Changing gearing is as easy as changing the pinion. A Smaller pinion (less teeth) will give less top end speed but more accelleration. Transverlsey putting a bigger pinion on will have the opposite efffect so less accelleration but more top end speed.

You can also change the spur gear size to adjust gearing. A Smaller spur (less amount of teeth) will gear the car up so you will have less accelleration but more top end and using a bigger spur gear will gear the car down so you will have more accelleration but more less top end speed.

I have attached a gear chart that I have created for x2-x2c cars which show overall ratios depending on what pinion spur combination you are using which you might find useful.

HTH

[Steven Forster]

Originally Posted by Robbiejuk

The two numbers that people are putting down are the pinion / spur gear sizes.

In your example 23/80 would be read as having a 23 tooth pinion (Small metal gear attached to motor) and and 80 tooth spur gear (Larger usualy plastic gear mounted on the layshaft for the gear box.)

Changing gearing is as easy as changing the pinion. A Smaller pinion (less teeth) will give less top end speed but more accelleration. Transverlsey putting a bigger pinion on will have the opposite efffect so less accelleration but more top end speed.

You can also change the spur gear size to adjust gearing. A Smaller spur (less amount of teeth) will gear the car up so you will have less accelleration but more top end and using a bigger spur gear will gear the car down so you will have more accelleration but more less top end speed.

I have attached a gear chart that I have created for x2-x2c cars which show overall ratios depending on what pinion spur combination you are using which you might find useful.

HTH

Is there a set gear ratio which you need to be aiming for to give you the best balance between acceleration/top speed from any given motor/pinion/spur gear combination so not to have the motor screaming with too fast an acceleration or too tall and getting too hot, if that makes any sense..............

cheers

[Robbiejuk]

Not really, dependant on track. I usually gear mine so it gets to full speed about 3/4 of the way down the straight.

[Chris56]

It also depends on which motor you are running: a fast motor (say 6.5t) is generally geared lower than a slower one (9.5T). Many motors will come with a recommended Final Drive Ratio that you should aim for (these are what the numbers relate to in Rob's table).
I run a 6.5T in my Losi 22 and have a final drive ratio of 9.23 (20/76). This could be a good starting point as it gives me a good balance of speed/acceleration without getting too hot.

[deano261]

cheers guys so would a 23/80 be ok to go racing with on a brushless motor

[StevieG]

Hi,

I have been running an xcelorin 8.5T on 80 spur 24T pinion on grass, the motor is only just warm coming off after 5mins, also the car has a good balance of low and top end speed.

Always better to start low though.

[Battle_axe]

I run a 23/80 with a 6.5 in my car it seems to work on most uk tracks very well

[Steven Forster]

Originally Posted by Chris56

It also depends on which motor you are running: a fast motor (say 6.5t) is generally geared lower than a slower one (9.5T). Many motors will come with a recommended Final Drive Ratio that you should aim for (these are what the numbers relate to in Rob's table).
I run a 6.5T in my Losi 22 and have a final drive ratio of 9.23 (20/76). This could be a good starting point as it gives me a good balance of speed/acceleration without getting too hot.

Thanks for the reply, this was something i was looking for

[Steven Forster]

Originally Posted by Chris56

It also depends on which motor you are running: a fast motor (say 6.5t) is generally geared lower than a slower one (9.5T). Many motors will come with a recommended Final Drive Ratio that you should aim for (these are what the numbers relate to in Rob's table).
I run a 6.5T in my Losi 22 and have a final drive ratio of 9.23 (20/76). This could be a good starting point as it gives me a good balance of speed/acceleration without getting too hot.

----------------------------------------------------------------------

Lets see if ive worked this out right.........PLEASE correct me if im wrong

(B4 internal ratio is 2.6)

my LRP Eraser 9.5t brushless motor recommended final drive ratio is 9.4:1 so for me to get that ratio or as close as possible

(with the only spur gear ive got 81),

I would have to run a 22/81 pinion and spur combo to give me a final drive ratio of 9.57...........???

And think ive read before that if needing more acceleration drop done 1 tooth to 21 or for more speed up 1 tooth to 23 but not recommended to to go up/down more than 1 tooth.........???

cheers

[Chris56]

That is correct, I always use FDR = (spur/pinion) x internal ratio. With each car I buy I just plug this formula and some spur/pinion values into excel and hey presto, i've got a gear chart!

Unless the performance/motor heating is drastically out, i also tend to just change one tooth at a time

[Steven Forster]

Originally Posted by Chris56

That is correct, I always use FDR = (spur/pinion) x internal ratio. With each car I buy I just plug this formula and some spur/pinion values into excel and hey presto, i've got a gear chart!

Unless the performance/motor heating is drastically out, i also tend to just change one tooth at a time

I think something might be wrong as i havnt got a 22t pinion so running 23/81 and the 9.5t motor is getting really hot and also cogging at low rpms using a Mamba Max ESC, whereas if i put my 6.5t motor in and use 23/81 ratio it gets warm but very little to almost no cogging........

[Chris56]

Originally Posted by dexter24

I think something might be wrong as i havnt got a 22t pinion so running 23/81 and the 9.5t motor is getting really hot and also cogging at low rpms using a Mamba Max ESC, whereas if i put my 6.5t motor in and use 23/81 ratio it gets warm but very little to almost no cogging........

In my Losi 22 i run an Xcelorin 6.5 with 20:76, giving an FDR of 9.23 and it doen't overheat neither.

Maybe try going up a pinion size or 2 as overheating can also occur if a car is undergeared (a bit like if you go for a run but take lots of short, quick steps and your legs feel tired). Is the esc getting hot or just the motor?

[Yoc]

Originally Posted by dexter24

I think something might be wrong as i havnt got a 22t pinion so running 23/81 and the 9.5t motor is getting really hot and also cogging at low rpms using a Mamba Max ESC, whereas if i put my 6.5t motor in and use 23/81 ratio it gets warm but very little to almost no cogging........

The only problem I see here is the LRP Eraser motor. This is a very bad brushless motor. I used to have a brand new Nosram Dragon 10.5 (same motor as your LRP branded by Nosram) and it was so hot (was forced to let it become cold after a few running minutes) for so poor performances... I changed for a Feigao 6.5 and everything became cold ! And this was not a ratio problem.

[Mad-Wolfie]

Originally Posted by Chris56

That is correct, I always use FDR = (spur/pinion) x internal ratio. With each car I buy I just plug this formula and some spur/pinion values into excel and hey presto, i've got a gear chart!

www.gearchart.com

Plus the B4 is already listed in the drop down.