gearing for 12m

[burgie]

hi - can anyone suggest a suitable gearing for a 12m, running stock motor. I would prefer the gearing suggestions as spur/pinion combination 'cos I don't understand mm/rev!!

thanks

[rice98w]

its ni-on impossible to give you a specific spur/pinion combo... you really need to get to grips with mmpr.. the information acquired when using mmpr is indespensable!

you have a corally right? take a look in the back of the instruction manual and there is alot of charts... now take a decent ruler or a pair of verniers and accurately!! measure your rear tires (fronts have no relevance to mmpr) now lets say you rear tire was 50mm..

goto the 50mm chart, look up what spur you are using and go across till you get to a decent number... if you are using modified try about 37mmpr.

matt

[MikeS]

Chris, I am, rightly or wrongly, assuming that you are "new" to 1/12th and probably have experience of Tourers. If not I apologize.

Unlike TC's running rubber tyres, all 1/12th run on foam tyres, which wear slightly during each run. Unlike the TC rubber tyres which maintain a fairly consistent diameter during their whole life (not absolutely true, but close enough to be) foam tyres will wear down a lot compared, and if you are using only one set of tyres, then they will wear down quite a lot and rapidly. Enough to noticeably alter your cars effective gearing. This is one of the reasons why the 1/12th racers use multiple sets of tyres, to reduce the tyre wear rate, which increases their life, and keeps the handling, grip (since they can "recover" between additive applications) and gearing is then more consistent from run to run. The upshot of this wear is that you should ideally monitor the diameter of your tyres, particularly the backs, since they affect not only the handling, but also the gearing as well.

MMPR, or millimeters per revolution, is simply a way of expressing the gearing of your car in terms of millimeters of travel of the car, for one revolution of the motor armature. The beauty of this is that it is transferable. And with the use of tables or a calculator, once you know the gearing of your motor that works best for your track/car/style/cells etc, then if you use the mmpr value, as your (rear) tyres wear down or are changed, armed with the diameter of the tyre, you can simply look up the figures on your gearing chart, to see when and by how much you need to change your gearing, the pinion and/or the spur, to maintain this ratio.

This method also makes life a lot easier, as over time you will accumulate more sets of tyres, and they will inevitably be of different diameters, using your mmpr figure that suits your motor/car/....etc, then looking this up on the chart (or calculating it) you can quickly determine what pinion/spur will give you the correct gearing for the motor.

For actual gearing values, this really does depend on the motor (stock in this case) track size and your thumbs! Ideally you should check with other racers, at the same track, what sort of gearing they are running, then fine tune this to suit your motor/style....etc..... But as Matt has indicated, your gearing is important and can be anywhere from 33 mmpr to 43 mmpr, get a guide from others, then only running will allow you to adjust it to suit from there.

Good luck ;)

[rice98w]

(stock in this case)

sorry i thought it was mod! :-[

you might want a higher mmpr for stock!

[burgie]

mike - don't worry, you are almost correct! Gave up tourers 12 months ago, and went back to buggies. Bought a mardave and now got a 12th, so yes, I am entirely new to this little lot. Thanks for your help though, it is appreciated. Now for a typically dumb question. How do you measure one revolution of the armature? I'm guessing you put a mark on the pinion do you? and a mark on the bench/tyre to measure the distance travelled?

[MikeS]

Chris, you don't need to measure it!
Just measure the diameter of your rear tyres then use the chart. You have your spur size and your pinion size, using these 3 values, the chart will tell you what the mmpr is.

[steven bough]

lol..
Chris do you have a Team Corally manual???

[burgie]

yeah, yeah, I know . . . Oh look is that egg on my face! Please forgive me, and make way for the worlds biggest D'OH!!!!!!!!!!!!!!1111 ;D

[steven bough]

Have you managed to get your head around it?
it is hard to understand when you first start using it..

[burgie]

yeah - thanks to a clear head and Mike at Modeltech - I only wish that I had used that principle when I was running touring cars. It really is a wonderfully simple concept. I think all the numbers, and big words like "vernier" scared me! lol. ;D