Newbie Gearing Question

S

sith_ranger

New Member
Have a HF 79cc going on a bike with 26" tires. Engine will be keeping the governor so 3600-4000rmp (gov tweek if I can figure that out). Thinking of running a jackshaft with 11 tooth clutch, 22 tooth input, 9 tooth output, to a 48 tooth rear. If I figured right should be a 10.67 final. Will that get me max 29-30mph and still be able to climb small hills?
 
i am running the same motor and the same jackshaft your talking aboutbut my rear sprocket is 44t and wheel is 24 inch rim.
its not going to do super great on hills but your cruise will be perfect. keep looking around to see what ohters have done then gauge for your self.

a word of advice if you do get the that jackshaft also pick some spacers and a half link
 
That's a bit high, a ratio in the 12:1 range would be better, but 10.67 definitely doable.

I have one governed bike. I run an old derailleur thumb shifter as a throttle. Its a set it forget it type of cruise control as the throttle locks where you leave it and the governor does the rest. I have found that using a governor with a twist throttle caused a bit of surging and worked better less the gov. Just my thoughts.
 
I've built several 79cc bikes, and I'd recommend a 13:1 ratio. It will give you a top speed of about 36 mph, and have plenty of torque. btw if you do gearing of 11-36-9-36 that gives you 13:1. Mine all have the governor removed though, it's not that hard to do and totally worth it.
 
After rearranging the formula for gear ratio to solve for speed a 13:1 ratio would require the engine to hit 5,040 RPM to reach 30mph. Can anyone confirm?
 
Yep. I ran some ratios thru my gear calc and that is basically correct for a 26". Depends on the size of tire use to be exact.
 
Thanks CannonBall,
I hope to adjust the governor to let me have about 4000rpm. That should let me hit about 28-29mph tops with a 10.67:1 ratio. (48 Tooth) I don't have a lot of hills around, mostly gradual changes in grade.
 
I couldn't use the calc, was not compatible with my browser. However I did it the long way on a calculator and it indicates right at 30mph@5100. I missed the speed in the post at 36, for some reason thinking 30. My mistake.

My calc call GearRat(downloadable on line) is dead nuts accurate and allows for multiple reductions(up to 5) and friction drive. Been using it for years. Great tool.

Mat Man personal question. Ever work as a Volvo tech? Knew a guy with that nickname that did, and he moved from the Atlanta area to Athens.
 
6100 rpm is about where the valves float. AGK talks about stiffer springs.
I have not found anything about adding shims or washers for more preload.


Wayne_z's, with V-belt primary:

99cc Preddy 2 speed, takeoff in high gear, 46MPH!
https://www.youtube.com/watch?v=Jk_RyiyI6L4

Hi CB2
I only wish I was a car mechanic because some of the best make $70k.
I was just a Lab Tech involved in test, calibration, maintenance for manufacturing,
All of them moving for cheaper labor.
Sorry about late response, I had water flooding issue.
 
Thats funny mat man, the whole time I was twisting wrenches I was wishing I had a job like a lab tech. Did make decent money though.
 
I met a guy that was same age, making a little more than me.
He had a 4 year accounting degree. He was a GM Dealer Mechanic
that mainly did electrical and A/C. It paid more than accounting.
That would have to had been my gig, because of my limited wrench ability.

Had a good friend that graduated one of the top 2 year Diesel colleges in the country.
Bought $2K of tools. Worked less than 1 year and went into his wife's family sign business.

Funny how things work out.
 
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