[Kartbuilding] gearing question

Stephen Burke sburke at burkesys.com
Thu Nov 2 10:51:56 GMT 2006


If you are using 5" wheels - and typically a motorbike would have ~20" 
wheels - using the same sprockets and chain would get you 1/4 top speed of 
the motorbike.

If you want a racing kart - ideally you would have AS FEW GEARS AS 
POSSIBLE. The majority of racing karts dont have any gears - so there is 
no time wasted changing gears. The engines they use have a very high rpm 
(+20,000rpm !!), and are of the two-stroke vareity.

If you are going to use an engine off a dirt bike, as you suggested, you 
are going to have to go looking for smaller sprockets for the rear axle, 
in order to bring the speed back up.

As for Differential versus Straight rear axle - I would go with Straight 
Rear axle. Less hassle, just as effective if the steering geometry is 
setup correctly. Of course tire wear will be increased greatly - and it 
might not be as good on wet tarmac. The differential is the ideal 
solution, but its heavy and it has more gearing (down) which you would 
need to worry about.

Best of Luck,

On Fri, 27 Oct 2006, Bill wrote:

> Im getting ready to build a race cart and dont know what type of gearing to give it.
I plan on running either a 125 or 250cc engine with a 6 speed
(or however many gears dirt bikes usually come with) transmission.
Ill be using 5" wheels all the way around. So my question is, how should I gear this?
I want it to be fast of course since its a race cart. Id like to be able to do around 70-75mph or so.
This will be a well built cart so construction and safety will not be a problem.
> One other question now that I think about it is,
should i run a differential or just a straight axle with a sprocket?

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