Jack Shaft Help??

[Jsmith813]

Im building a go kart with a YTZ250 2 stroke engine. I want it to have good acceleration with a fastt Top speed. I have 16in tires.an the drive sprocket is a 15Tooth but can be changed if needed. Please help I was kinda thinkn of using to jack shaft set ups to have a real good top end an good acceleration. Im not sure what size i need sprockets i should use Reply soon Thanks

 

[OzFab]

Using a sprocket that's similar in size to the original bike is usually the way to go. Even with the smaller tyres, you should get pretty good acceleration & a decent top speed.

Why use a jackshaft?

BTW: Your (so far) other post was a bit pointless; that thread is 3 years old. It's extremely unlikely you'll get a response. Good on you for searching but, choose carefully.

Oh, & to the forum

 

[denhammotors]

Please help I was kinda thinkn of using to jack shaft set ups to have a real good top end an good acceleration

A jackshaft will not give you good acceleration and high top end. You would have good low end torque with a jackshaft, but for high top speed, I would just stick with the bike's original gearing.

 

[Jsmith813]

Yeah

Well stock gearing is 13/42...with 22 in tires... i just dont thnk it will have much speed.. :/

 

[OzFab]

According to our speed calculator, you'll get 85mph @ 5000rpm (which is mild for a 2 stroke) using 16" tyres & 15/42 gearing. Is that not fast enough?

 

[denhammotors]

According to our speed calculator, you'll get 85mph @ 5000rpm (which is mild for a 2 stroke) using 16" tyres & 15/42 gearing. Is that not fast enough?

Remember, 5000 rpm at the crankshaft will almost certainly be faster than at the countershaft sprocket on a motorcycle. To properly calculate the top speed, one must know the primary drive ratio and all of the transmission ratios (assuming this engine does have a gearbox). The front sprocket RPM is usually about 1/3 of the crankshaft's.

 

[OzFab]

That's a good point; I was working on a 1:1 output ratio

 

[Jsmith813]

Ohh

Could anyone look it up for me?? I cant find it... Its a 1986 Yamaha Tri Z 250... An Those Calculations Dont Include weight an friction into the situation. But I thank you all for helping

 

[landuse]

Could anyone look it up for me?? I cant find it... Its a 1986 Yamaha Tri Z 250... An Those Calculations Dont Include weight an friction into the situation. But I thank you all for helping

Weight does affect speed a bit, bit friction you can forget about. It will be negligible

 

[denhammotors]

Could anyone look it up for me?? I cant find it... Its a 1986 Yamaha Tri Z 250... An Those Calculations Dont Include weight an friction into the situation. But I thank you all for helping

This is all I can find. No gearbox ratios here, though.
http://web.ebscohost.com/serrc/pdf?...af85-05da08c90170@sessionmgr113&vid=5&hid=107

 

[landuse]

I found a service manual HERE. I wasn't going to download it to have a look, but I am sure it would have ratios in there.

I just googled "Yamaha Tri Z 250 manual". I got several hits you might look at yourself

 

[denhammotors]

Found it
Primary reduction ratio- 2.625:1
Secondary reduction ratio- 3.384:1
1st gear- 2.384:1
2nd gear- 1.75:1
3rd gear- 1.411:1
4th gear- 1.142:1
5th gear- 0.956:1

 

[landuse]

Found it
Primary reduction ratio- 2.625:1
Secondary reduction ratio- 3.384:1
1st gear- 2.384:1
2nd gear- 1.75:1
3rd gear- 1.411:1
4th gear- 1.142:1
5th gear- 0.956:1

Great