Gearing for a cross kart

[Tsoslow]

I am building a 2004 honda cbf500 powered cross kart with 20” tyres,
Currently the kart has a 42t rear sprocket and the engine has a 15t, if i can i would just keep this but could someone tell me if i need to change sprocket sizes and if it will be undriveable with the gearing i have now, thankyouView attachment IMG_3642.jpeg

 

[Master Hack]

You should be fine. There is enough power available that gearing isn’t a big issue.
Your 20 inch tires are about 4-6 inches smaller than the bike rear so your overall gearing is lower. You have a transmission also.
changing the gearing too much will leave either the low or high gears unusable.

 

[Tsoslow]

Will it fry the clutch trying to pull away or bog it down?

 

[anderkart]

I used this motorcycle gearing calculator: https://www.gearingcommander.com/

I substituted your karts 20"-tall rear-tire diameter (It's 62.83") & I also substituted your current rear sprocket (42-teeth):

That site lists your engine having 57 horsepower with a max/redline RPM of 9500...

According to that calculators results, here's the estimated-top speeds you could expect your cross kart to achieve in each gear, at 9500 rpm.
1st gear: 30mph
2nd: 46mph
3rd: 59mph
4th: 70mph
5th: 81mph
6th: 91mph

Your Cross Kart will be quite a bit heavier than the CBF motorcycle, so I'd expect lower top speeds than these results; especially in 4th, 5th and 6th gears.

I don't know what kind of terrain (or race tracks?) your planning on riding at, or what top speeds your expecting to achieve, but I think your 15-tooth counter sprocket & 42-tooth gearing should work out fine for now with your 20" rear tires, unless your kart ends up being extremely heavy.

PS: If your planning on riding at sand dunes or lots of low-speed steep mountain climbing trails, you might wanna consider steeper gearing with like a 12 or 13-tooth counter sprocket, and/or a rear sprocket in the 50-60 tooth range.

 

[Master Hack]

Will it fry the clutch trying to pull away or bog it down

Not likley. You have plenty of gears, there should be a gear for every situation. If you plan on terrain as in the example above, then you might consider lower gears. Changing the ratio too much and your first gear will be so low as to be useless.

 

[Tsoslow]

I used this motorcycle gearing calculator: https://www.gearingcommander.com/

I substituted your karts 20"-tall rear-tire diameter (It's 62.83") & I also substituted your current rear sprocket (42-teeth):

That site lists your engine having 57 horsepower with a max/redline RPM of 9500...

According to that calculators results, here's the estimated-top speeds you could expect your cross kart to achieve in each gear, at 9500 rpm.
1st gear: 30mph
2nd: 46mph
3rd: 59mph
4th: 70mph
5th: 81mph
6th: 91mph

Your Cross Kart will be quite a bit heavier than the CBF motorcycle, so I'd expect lower top speeds than these results; especially in 4th, 5th and 6th gears.

I don't know what kind of terrain (or race tracks?) your planning on riding at, or what top speeds your expecting to achieve, but I think your 15-tooth counter sprocket & 42-tooth gearing should work out fine for now with your 20" rear tires, unless your kart ends up being extremely heavy.

PS: If your planning on riding at sand dunes or lots of low-speed steep mountain climbing trails, you might wanna consider steeper gearing with like a 12 or 13-tooth counter sprocket, and/or a rear sprocket in the 50-60 tooth range.

Thankyou mostly soft off-road terrain mud bumpy fields nothing crazy

 

[ezcome-ezgo]

cbf500 powered cross kart

Nothing crazy

 

[Hellion]

I am building a 2004 honda cbf500 powered cross kart with 20” tyres

Sounds smashing, but...



Edited to add: you can upload pics directly to the site.