# Ratios?

#1
07-10-07, 06:02 PM
Member
Join Date: Jun 2006
Posts: 31
Ratios?

Hey guys,
The go kart i have built is now finished but i havent succeeded with the chosen drive! Atm i have a pulley drive and i tried it yesterday and no matter how tight i made the belt the belt would slip on the clutch. So im deciding to change to sprocket and chain driven, is this a wise decision? i think it will definately minimise this slippage. I havent actually got my sprokets yet but i know someone who has a great deal of them, i just want to know the best ratio to pick. Many sites on the net say the best is a 6:1 ratio but i tried a calcultor on the net and it will only do 37 km/hour, considering the wheel diameter and so on. If i reduce the ratio i.e. to 2:1 it will definately increase the speed. But why doesnt the net mention a smaller ratio? Is there something wrong with the smaller ratio?

Just a couple of specs if it helps:
Kart itself weighs 90kg with the engine
Rear wheel diameter is 26cm
Engine 192cc 5hp

Thankyou in avance!

#2
07-10-07, 06:37 PM
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,821
The higher the ratio, the harder it's going to be for the engine to move it. That's probably the problem you have now with the belt setup if it's slipping like that. Also, if the belt and pullies are properly matched and tensioned, it should stall the engine before it is able to slip.

A 2 to 1 ratio isn't going to work. You don't have enough power to get it moving from a standstill. Not to mention, 2:1 would be screaming fast if you did have enough engine. Way too fast. How are you figuring your ratio?

If you have a 5hp engine running at 3600 rpm, and a tire that is 2 1/2 feet around the tread, and a 6 to 1 ratio, you would be around 17mph. A 4:1 ratio would be 25.5 mph. A higher ratio would require much more hp. You might think about using a variable ratio drive, or higher engine speed (wears out the engine faster), or other options.

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