Confused about gearing? Read this

[Garry]

Gearing can be a minefield, if you don't understand what's happening in the car. Hopefully this guide should make it clearer to why your car isn't as fast as it can be, or why its too fast!

OK, any given motor has a powerband. It is the point that the motor starts spinning, to the point the RPM stops increasing. Thanks to the design of electric motors, the powerband is massive, but you still need to gear the car correctly to make best use of the powerband. For example, a motor geared for high top speed will be really sluggish out of corners, and may never hit the sweet spot of the powerband before you need to turn.

So, how do you gear a car correctly? First, you need to know the gearing you're on.

Electric cars usually have one pinion and one spur gear. The smaller gear is the pinion, the larger one is the spur gear. To work out the gearing, you can use a great website such as http://www.gearchart.com/ but if your car isn't listed, you'll need to do a little maths. Its Spur Gear divided by Pinion Gear times Internal Ratio equals Final Drive Ratio.

Spur

(----------) x IR = FDR

Pinion

So, with some random numbers:

89t

(----------) x 2.1 = 8.49FDR

22t

To make it a little easier if you're away from a calculator or a computer, a lot of cars these days come with a gear chart in the manual.

Here's the possible pinions and spurs that fit a Tamiya TT01, and the motor mounting holes you'll need to get the right mesh, that won't strip the gears.

The numbers in the middle of the chart are the Final Drive Ratio, along the top are the spur gears, and the pinions are down the side.

OK, you now know your FDR, but what does that mean to you?

Well, the FDR number is the amount of times the motor turns for one revolution of the wheel. Using our example above, the motor turns 8.49 times for every one complete turn of the wheel.

Lower FDR's mean more top speed, higher FDR's mean more acceleration.

In general, when you fit a faster motor, you fit a higher FDR. Fit a slower motor and you need a low FDR. That doesn't take into account the space you've got to run the car in, so smaller areas mean a higher FDR as you're not going to be able to reach the top speed with a low FDR, so its always a balance of top speed and acceleration that match the motor and the area. For touring cars at least, FDR's of 7.5 or above (smaller number) are considered high.

Its a lot easier to gear a motor for a track, simply gear the car so the car stops accelerating about two thirds (2/3s) to three quarters (3/4) of the way down the longest straight on the track

So, in summary....

If you are:

fitting a faster motor

driving on a tight track or small space

using more voltage/cells

fit a smaller pinion/bigger spur/high FDR.

If you are:

fitting a slower motor

driving on a open track or big space

fit a bigger pinion/small spur/low FDR.

But remember, everyone has a different driving style, different equipment setup etc, so no-one can say ''Use 'xyz'FDR with this motor or that track'', its really a case of trial and error. Look on eBay and buy a selection of pinions and try for yourself!

[B-Master]

another amazing refrance garry very informative and lots of help thanks

[adamwatkins]

hi, can anyone help with gearing options and motor positions for TA-05. Kinda need the pic you have abouve in this post ... but for TA-05 not TT-01, cheers if you can help !

[Garry]

From the TA05 manual:

You might be able to fit a bigger pinion on than a 25t, not 100% sure.

[adamwatkins]

cheers, assuming 105 pinion is standard

[mad-wolfie]

Don't forget old faithful...

http://gearchart.com/index.cfm?fuseaction=chart.create

The problem is though sometimes it's hard to work out the internal ratio of the car. This can be a problem so you have to either reverse engineer the ratio with old fashioned maths & work out from there what is going on or hunt for hours on websites as many manuals don't list the car internal ratio's. On that site you have options, but if your car isn't in the list you can enter the internal ratio & print off a chart

You can also work out the top speed on your car if you know what RPM your motor runs at- it won't be 100% accurate as it doesn't consider things like downforce generated from the bodyshell, tyres, the cars total weight, drag on the motor, etc etc, but it will give you an idea in the ballpark to help set your car up & how gearing changes affect the top speed & performance.

It's quite funny, sometimes at race meetings.. you know people are using the gear chart site when setting their car up as they access the site on a mobile phone or Wi-fi & you often still hear the background music it plays.

[nitrorhys]

So if i was doing speed runs and i wanted my car to go fast i would fit a bigger pinion and small spur

Edited December 27, 2008 by nitrorhys

[Garry]

Yup.

[nitrorhys]

Yup.

Thanks garry you the man

[ta05]

Another thing to remember is that some motors are rpm based and some are torque based motors, others are a happy medium of both.

Motors that rev lots will lack torque. Torque is needed on smaller, twistier tracks, were acceleration is more important.

A larger track (such as aldershot) can be suited to an rpm based motor if you're able to keep the speed of the car up.

[amnesia]

I have knocked up a noddy excel spreadsheet to calculate gearing and theoretical (unloaded) max speeds on my TA-05.

I thought I would host it so that others can use it, if suitable for their chassis - not sure how shaft drive ratios are calculated. I guess I could do a version where the internal ratio is manually entered instead of calculated.

If I get bored over the weekend I will probably expand this to show all pinion / spur ratios within a +/- 10 tooth range or something.

Anyway, feel free to have a look...

Right Click & Save As

Cheers,

Daniel.

[Perko]

Thanks very much for this brilliant advice Garry - joined this forum today after ordering my first RC car from Modelsport UK earlier in the month (A Gravel Hound). Been trying to get my head around gearing for a week - This info and link to the gearchart website is invaluable - Understand it completely now! A must for all newbies like myself.

Thanks again and congratulations on what I consider to be the best RC forum on the web!

[mad-wolfie]

Thanks very much for this brilliant advice Garry - joined this forum today after ordering my first RC car from Modelsport UK earlier in the month (A Gravel Hound). Been trying to get my head around gearing for a week - This info and link to the gearchart website is invaluable - Understand it completely now! A must for all newbies like myself.

the Gravel hound uses the same gearing system as the TT-01 (as shown in Garry's chart) as the drivetrains are identical, so in theory you can run TT-01 gears & achieve the same ratio. This would of course give you additional speed because of the diameter of the wheels, but the acceleration would suffer.

The DF-02 has 2 choices of spur - the 70t & a 67t spur sold as a hop-up.

I put a gearing chart on my website that caters for both the DF-02 & the TT-01

http://www.ianmaddock.co.uk/?p=44

[gimpex]

I hope its okay to ask gearing related questions here , otherwise please close and I will open new thread.

- Where does one get this chart ( as TT01 above ) for other models ( like TA05 ) - the mentioned website shows only the FDR calc for all possibilities

- what does one mean when you say only certain gears and pinions can go together , and as per above chart 26/58 for example is not listed ?

- I have seen reference to a 48p ( I hope thats correct) what does that mean ?

Thanks a lot for sharing the info

[Garry]

- Where does one get this chart ( as TT01 above ) for other models ( like TA05 ) - the mentioned website shows only the FDR calc for all possibilities

Most of the time, you can get a gear chart for your car in the kit manual, but they don't always list full charts for space reasons. A TA05 manual has the chart listed above in it (just the kit spur gear), but its very chassis specific. The other options are to Google like crazy and hope someone's made one, or get busy with Excel or something, and create your own (but that would take a mighty long time ).

- what does one mean when you say only certain gears and pinions can go together , and as per above chart 26/58 for example is not listed ?

The will mean that a small pinion probably can't mesh with a small spur gear (and big pinion with big spur) because you can't physically move the motor into the right position to get it meshed. With my Xray T2'008 on 64dp and a 104t spur, the smallest pinion I can fit is a 30t one.

- I have seen reference to a 48p ( I hope thats correct) what does that mean ?

DP stands for diametric pitch, its the angle and profile of the tooth of a gear. For RC use these days, there are a few types of gears on sale:

Imperial:

32dp (Mardaves, E-Maxx's, E-Revos etc. Aggressive pitch so noisey, but very strong)

48dp (Majority of cars on the market, long lasting and fairly quiet)

64dp (High-end race chassis (touring cars, 1/12th etc), very fine pitch, very quiet and efficient, but weak)

Metric:

Mod-1 (1/8th buggy conversions, very aggressive, noisy but silly strong)

0.6 Mod (Tamiya pitch, TT01, TL01 etc, strong and noisey)

0.5 Mod (Tamiya pitch, TA04 etc, finer pitch, quiet)

0.4 Mod (Tamiya racing chassis pitch, TRF 415 range etc, very fine pitch, but weak)

(note, Tamiya never released a list of what runs what, so these 0.4/5/6 listings *may* be wrong)

Pitches can't be mixed (48dp pinion with 64dp spur etc. Metric and Imperial can be mixed, but they will wear themselves out over time, so its not really worth it.

48dp is the most popular gear pitch on the market.

[gimpex]

Thanks again Garry

[amnesia]

The gearchart I posted in post #11 will work with ANY chassis as long as you can work out your internal ratio.

the size of the pitch has no bearing on the ratio between the spur and pinion - ie a 75t spur and 25t pinion will give the same ratio on 48dp and 64dp of 3:1

If you want a higher top speed, use a lower Final Drive Ratio (FDR)... if you want quicker acceleration, use a higher FDR. Watch out for motor temps though with very low / high FDRs - all motors have an optimum range that will delivery best performance / longevity.

Daniel.

[madwestmo]

Hi,

Having some problems gearing my touring car , I run a cyclone TC which has a internal of 2.16 , im running a speed passion 13.5 brushless motor with a speed passion GT2.0 LPF ESC , for the track i race at i want to be around 4.7-5 FDR , Currently i use 48dp gears due to the track been outside to avoid stripping etc (cyclone's use 64dp as standard)

Now i use a 78t spur and a 33t pinion which brings me out at 5.11 FDR but my motor is extremely hot after a 5minute race (cant hold thumb on it for more than 2 seconds)

To reduce motor temps do i have to go smaller on the spur and smaller on the pinion but still achieving a FDR of 5 , for example 70t spur + 30t pinion , will this lower my temps ?? will this still give me the same top speed ?? wud this even mesh ??

Thanks for any help

PS this is on rubber tyres too

[Garry]

Changing the spur and pinion doesn't make a difference if the FDR is kept the same.

How do you know you need an FDR of 4.7-5? If its what others are running and you're very close, but its getting hot, I'd say theres something else causing the heat. Either mechanical like a tight drivetrain, loose diff or binding bearing, or something electrical in the ESC settings like drive frequency or timing.

[madwestmo]

timing is at 0 , drive frq is at default , everything mechanically seems to be running fine as is the diff

is it not true running a smaller pinion will keep the temps down ?

[Garry]

Yeah, but changing the spur at the same time to stay on the same FDR means you're not changing anything, its the same effort used to move the car, so generates the same heat.

[madwestmo]

is the profile on my esc going to change my temperatures much ? it has 1-9 (smooth-aggressive)

thanks for all the help so far

[Garry]

Yep, the more agressive it is, the quicker it heats up.

[amnesia]

The only thing I can think is that the motor has dodgy bearings or something.

It's weird.

Edited September 4, 2009 by amnesia

[alice-edmund]

One question on gearing - how much play should there be between the pinion and the spur? Having them with no 'play' surely leads to lots of wear - but too far apart would mean just the tips of the teeth touching - which would again give lots of wear - and possibly break the teeth of the spur gear if shock loaded?

Any advice on this?