hi, we are planning on using a 14t motor sprocket but still are not sure which sizes we should use as we are hoping for 2 speed set up: 48 and 60 or 60 and 72?
The previous team used a 12t and 48t with the kit car which quite obviously resulted in the motor burning out. However, this time we are still using the greenpower sprockets but are using an aluminium frame and the driver will be much lighter.
Do you have any suggestions that you think might help our gear system?

thank you


  • Might I ask a reason you're opting for a multi-gear setup? As you're a kit car, I'd make the assumption you're running F24. You must remember that torque curves of an EV are not the same as an ICE so your drivers may struggle with changing to the gear most useful to them without some kind of display of current draw or another factor you wish to keep the same.
    Why don't you look at the average speed of your main competitors, gear a few teeth above it to offset battery voltage decrease and slowing caused by drag, rolling resistance etc. A system with 2 relays, one for 12v power and another for 24v, will allow you to cheaply and easily decrease current spiking experienced when starting the motor up. Also think about motor cooling - fans, perhaps air intakes etc as this may have been a partial culprit in your burnt-out motor.
    To help you out (if you've not already done this) I've calculated theoretical speeds (that is, the speed the car will do with the motor spinning at 1800 RPM, apparently the motor's most efficient speed. Do not take this as correct as I am unsure about that. This is also done on the assumption that you're running 20" wheels as you have a kit car
    For your first idea, you have a low ratio of 24.98mph and a high ratio of 31.23mph. This is quite obviously too high for a kit car, and will not last for 90 mins on one set of batteries if it doesn't burn the motor out, which it probably will.
    Your second idea has a low ratio of 20.82mph and high ratio of 24.98mph. This is more sensible if you decide to continue with the multi-gear idea.
    Derailleurs can often throw off chains if not set up quite rightly too, which could be an issue.
    I suggest you consider what your competitors do too, if it works for them it will for you
  • If the chassis has been replaced with an aluminium one, even if a direct copy of the steel one, does it not fall outside of the kit car category?
  • I'd assume it doesn't, after all it's not actually a kit car anymore but a copy of one. Status Mk 1 can't run kit car for this reason as far as I'm aware.
  • We re-built the Steel kit car in aluminum and was no longer able to race it as a kit car.
  • Just paint it.... tee.....hee!!!!!!
  • Bearing in mind this is a gears thread, I'm currently writing a code in Python to calculate gear ratios. It's not done yet, but if anyone's interested let me know as I'm happy to allow other teams to use it for their Greenpower ventures. Would love to help some other teams.
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