[Kartbuilding] question about sprocket

Stephen Burke sburke at burkesys.com
Sat Sep 6 16:18:29 IST 2008

Hi Jernej,

The gear ratio (size of drive and driven sprockets) depends a lot on the 
following factors:
1. The size of the Rear Wheels
2. The RPM of the engine

Typically for a standard racing kart (as in 
) with a rear wheel diameter of 250mm and a 5hp engine with 5000rpm (max), 
the gear ratio would be 5:1 (most common gear ratio used). There would be 
a sprocket with 10 teeth on the engine, and a large sprocket with 50 teeth 
(approx) on the rear axle.
Engine sprocket with 10teeth: 
Large rear sprocket with approx 50 teeth: 

What I would recommend however is the following:
Look at the following 3 photos:
To enable quick and easy changing of the rear sprocket (to try different 
sizes), cut a piece out of the sprocket with a narrow angle-grinder. Once 
the new sprocket is bolted onto the rear axle, it can be re-welded 
together. I have used this method which works perfectly. This allowed me 
to experiment with different sizes of rear sprockets, and saved me from 
having to remove bearings, wheels etc. when replacing the sprocket.

As a result I would suggest the following:
Get a small sprocket with between 10 and 15 teeth for the engine.
Get a couple of different sized sprockets with between 40 and 70 teeth for 
the rear axle.

Lastly, if you want to calculate the estimated speed of your kart, take a 
read of the following webpage:

As far as chains go, take a look at the following photo:
The one on the left is a bycycle chain. On the right is the chain I used 
for the kart. Unforunately I forget the exact specs of the chain, but it's 
a standard one used on commercial karts (as in photo above). (From looking 
at the chain photos, I can make out KCM - 428H as the type of chain). A 
chain splitter can be used to take the chain down to the correct length ( 
) and a split link used to join the chain back together.

I hope this answers some of your questions.

Best of luck,

On Fri, 5 Sep 2008, jernej knez wrote:

> Hello,
> I am trying to make a new kart, and before actual production, I have
> to make few things a bit brighter. I would like to know;
> -how many teeth does main sprocket have
> -how many teeth does a little sprovket have (on the engine), therefore
> I can calculate my gear ratio
> -which is the most common gear ratio used in karting;
> i=z2/z1=???
> -which chain have you used? I am most interested in chain type DIN 8187  08 B .
> is this a proper chain to use, or should I choose a heavier one ( 10
> B or even 12 B )??
> I have ability to make my own sprockets, since my family has a company
> that produces machines and therfore has CNCs.
> Thanks for your time for answers,
> Best regards
> Jernej Knez
> MSK, Slovenia

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