Help

[bladedcoronet23]

I have a new kart build and it currently has a torque converter and a 36 tooth rear sprocket. To me that seems like a really tiny rear sprocket. i didn't get much riding time before it broke. I need a new sprocket to make the gear ratio right in the middle of torque and top speed. It has 16 in rear tires and the torque converter has a 12 sprocket. Does anyone know where i should start on sprocket size?

 

[milesguy81]

It depends if you want to offroad/hill climb or just ride on the street. A 72 tooth sprocket will give you 6:1, which is a good middle ground for acceleration and top speed. I have a kart with a 7:1 ratio and 16" tires and I hit 50 with a decently modded 301. I would go with a 72 tooth cause you can off road and have decent top speed + acceleration

Edit - Speed also depends on how fast your engine is revving, too. With big tires like the 16s, you need more torque than you would with little wheels. Its hard to decide on a ratio because we don't know what your use case is

 

[bladedcoronet23]

It depends if you want to offroad/hill climb or just ride on the street. A 72 tooth sprocket will give you 6:1, which is a good middle ground for acceleration and top speed. I have a kart with a 7:1 ratio and 16" tires and I hit 50 with a decently modded 301. I would go with a 72 tooth cause you can off road and have decent top speed + acceleration

Edit - Speed also depends on how fast your engine is revving, too. With big tires like the 16s, you need more torque than you would with little wheels. Its hard to decide on a ratio because we don't know what your use case is

It would mostly be hilly terrain and trails. And i have a stock 212 right now but im going to do a stage 2 build with .265 hot cam

 

[milesguy81]

A 6:1 (72 teeth) would have a decent amount of torque and would be the best for offroad and speed combo. If it feels underpowered you could always go to a 7:1 (84 teeth) Also what cvt are you using with that extra hp? I feel like a 30 series would burn through belts way fast. I had a 30 series on my stock 301 (8hp) and it burned through belts super fast.

 

[panchothedog]

With a 212cc engine a 30 series torque converter will work fine. 6 to 1 as mentioned by miles81 is the gold standard of gear ratios. But instead of running a 72 tooth on the axle, switch to a 10 tooth driver and a 60 tooth axle sprocket. With 16" rear tires, that 72 tooth could possibly present ground clearance problems.

 

[panchothedog]

Miles, the 301 needs a 40 series. I have one on my 301 powered kart. It's the torque that kills the belts,.not the horsepower. A 212 puts out 8 lb.ft. A 301 makes 14. Big difference. I have 212's that are built pretty strong, 14-15 horsepower, but they still don't produce enough torque to hurt the 30 series. Brand and quality of belt also has a lot to do with how long they last.

 

[milesguy81]

Miles, the 301 needs a 40 series. I have one on my 301 powered kart. It's the torque that kills the belts,.not the horsepower. A 212 puts out 8 lb.ft. A 301 makes 14. Big difference. I have 212's that are built pretty strong, 14-15 horsepower, but they still don't produce enough torque to hurt the 30 series. Brand and quality of belt also has a lot to do with how long they last.

Oh interesting... I guess that makes sense, I'm not sure why I didn't think about that before. Its also crazy the size and weight difference of the 30 series and 40 series