Gear Ratios

[andyman1331]

Hey guys, Well for my grade 11 small engines project i am building a go kart i have 24 feet of 1 1/4 diameter steel pipe with a .095 wall and i am welding a frame up. I have a 1969 briggs 4.5 hp and i need some help with gear ratios i thought of getting a 12 tooth centrifugal clutch and a 60 tooth sprocket on an old lawn tractor diff and i will be using 13" diameter tires so it would be a 5:1 ratio and i was wondering if that would give me a good top speed but still get me rolling any help would be sweet thanks.

 

[Kaptain Krunch]

I would go with a 6:1

 

[freakboy]

i agree with dante but i wouldnt use a lawn mower diff... they suck.

 

[bajagokart]

6:1 is a nice ratio, tis what i use and works so good for me!

 

[Doc Sprocket]

I'm assuming you already have the lawn tractor rearend. Take some time to crack it open, and see if you think it's up to the task. Are the gears plastic, or cast junk? then probably not. Otherwise, go for it.
That old engine sounds neat, but I have to agree that you're likely better off with 6:1. There's kart speed calculators available all over the place (don't have link at the moment), use that to help determine your desired ratio. Remember that top speed is entirely dependent on having the power to achieve it. With 4.5hp, you may want to err on the lower side of gearing. For example, if you find 6:1 is ideal, maybe shoot for 6.5:1. Theoretical top speed may suffer, but if you're engine's weak, you may never attain that thoeretical number so it's pointless anyhow. Cheers- Chris

 

[andyman1331]

ok thanks a lot guys, i wont use a lawn tractor diff then i was still deciding wether or not to use it and i will go with a 6:1 ratio ill post another thread wen its all build thanks again

 

[Doc Sprocket]

Never say never. Check out the diff first, See if it's decent. And- Why not start a build thread and post all your progress, we love to see this stuff, and can help!