I'm Stuck On Sprockets!!

[Sumnig66]

Gearing Question.
Juat bought a brand new 140cc 4speed that comes stock with a 15t sprocket. This engine is going on this kart. What rear sprocket hub and sprockets should i order or should my rear sprocket be a small solid sprocket?

 

[Brianator]

What size rear tires are you going to be running? Measure from ground to top of tire, that diameter is a important factor in considering what rear gear to use. What kind of top speed you're after is another consideration.

 

[anderkart]

This link claims your engine comes with a #420-pitch counter sprocket with 15 teeth:
https://wholesale-cycle.com/140cc-piranha-engine/
Is that the exact model of engine you bought?

I can tell your karts has a metric sized axle, but you'll need to measure to cornfirm if its diameter is 40mm. or 50mm.

Then here's a link to some shifterkart sprockets made for 40mm & 50mm axles:
https://www.sharkshifter.com/index.php/top-parts/prt-sprockets/prtspkt-428-sprocket.html

Not sure how many teeth axle sprocket to recommend for your engine, but I'd probably select a 25 tooth if it was mine. Then you'll probably discover that you could buy larger/smaller counter sprockets for your engine if you ever decided to change the gearing later on.

Ok so here's the tricky part I'm not 100% sure of:

Your engines counter sprocket is the #420 pitch size, made for #420 chain...

Shifterkart sprockets (made to fit metric axles) are all made to fit the #428 size chain...

#420 & #428 are both the same 1/2" pitch size, but the #428 sprocket is 1/16" wider; and all the info I've been able to find state this combination will probably work ok together, as long as you use the #428 size chain.

But the best solution would be buying a #428 counter sprocket for your engine, for a perfect fit

 

[Sumnig66]

This link claims your engine comes with a #420-pitch counter sprocket with 15 teeth:
https://wholesale-cycle.com/140cc-piranha-engine/
Is that the exact model of engine you bought?

I can tell your karts has a metric sized axle, but you'll need to measure to cornfirm if its diameter is 40mm. or 50mm.

Then here's a link to some shifterkart sprockets made for 40mm & 50mm axles:
https://www.sharkshifter.com/index.php/top-parts/prt-sprockets/prtspkt-428-sprocket.html

Not sure how many teeth axle sprocket to recommend for your engine, but I'd probably select a 25 tooth if it was mine. Then you'll probably discover that you could buy larger/smaller counter sprockets for your engine if you ever decided to change the gearing later on.

Ok so here's the tricky part I'm not 100% sure of:

Your engines counter sprocket is the #420 pitch size, made for #420 chain...

Shifterkart sprockets (made to fit metric axles) are all made to fit the #428 size chain...

#420 & #428 are both the same 1/2" pitch size, but the #428 sprocket is 1/16" wider; and all the info I've been able to find state this combination will probably work ok together, as long as you use the #428 size chain.

But the best solution would be buying a #428 counter sprocket for your engine, for a perfect fit

So you are correct the engine comes with 15t #420.
My Axle is a 40mm so I think I found the hub I want. I just need to figure out the sprocket but I think I will pick up a 25t like you said to see how I like it. As far as the chain I did order a #428 for that very reason so I'll try it out but I'll look for a 15t #420 for the engine.

Aslo recommend the 25t sprockets I'm looking for?

 

[Sumnig66]

If I order this I wouldn't need to but a sprocket hub would I? This would mount straight to the axle?