How Do I Figure Sprocket/tire Sizes?

[PKRACING]

Can anybody help me fiigure out what would be the correct sprocket to run? We just started racing (3rd race) at a local 1/8 mile dirt oval in what they call the "YARD CART" class. Everyone is running 6HP. engines with the governers set at 4500 RPM or completely unhooked. We have a 12 tooth clutch, 72 tooth drive sprocket, and 15" tall tires and are being left in the dust. The other carts are running the same clutch and drive, but smaller rear tires, approximately 12" tall. Should I go to a smaller drive sprocket or a larger sprocket? One of the other racers suggested to step up to about an 80 tooth drive. Does this sound correct? We only have 1 race left and I would like to get it figured out.

[jmorga10]

i dont know for sure but i would think those bigger tires are robbing your kart of power. yes they will give a higher top end but take away from low end. a bigger sprocket would give you more torque. or a clutch with less teeth would give you more low end torque as well.

[jmorga10]

i guess it is a cvt system. im confused. :l i guess ill just start at a 6 to 1 and work from there.

[PKRACING]

Thanks for your reply. I guess after I reread my post, I wasn't real clear.
We're new to Kart racing and my terminology (?) isn't real good.
We have a 12 tooth centrifugal clutch and a 72 tooth driven sprocket.
I hope this makes it clear. Thanks again, appreciate it.

[jrjulien1]

i would suggest that you opt for the 12in tall tires and start tuning your gear ratio from there it might take a while to win some races but once u got the set up right youll do good and remember its not who wins or loses its who has the most fun

good luck

[PKRACING]

Unfortunately, I just spent $50 on new back tires, or I would switch to the smaller tire. The frame was mine when I was a kid and the tires were dry rotted. I replaced them with the same size not thinking. My boys say they're having fun, but you can tell by the look on their faces that they don't like being 1/2 to 3/4 of a lap behind at the end of a race. I just would like to get them up into the pack, so that they could really have fun and learn to respect the other drivers skill and gain some skills of their own. I appreciate any comments and suggestions. Thanks again.

[imported_robertdjung]

well, the tire size really is a big deal. We don't have a speed calculator here, I'll have to code one, but tire size definitely effects low end, top end.

[jrjulien1]

theres a speed calculator here http://webpages.charter.net/jeffparker/speed_calc.htm