need gear ratio input.

weldkingoc

weldkingoc

Active Member
#1
#1
So i have a 9HP vanguard/Briggs motor that i am mounting in a Bonanza frame with 6" kidney bean wheels. I will be running a jack shaft and my rear sprocket is going to be a #41 chain 40tooth sprocket and the clutch i am looking at is available in 14 or 17 teeth. My question is how many teeth should i run on the two jack shaft sprockets and clutch for a good all around versatile ratio to go with the 40tooth rear sprocket? I don't really remember how these ratios work
:shrug:
 
Motra

Motra

Active Member
#2
#2
Will you mostly just be riding on roads or climbing steep hills? With a 9HP engine you could get away with fairly high gearing, so you'd have pretty good top speed and still have good acceleration too.
 
weldkingoc

weldkingoc

Active Member
#3
#3
It will mostly be fairly flat ground. So say im running a 14 tooth clutch and a 40 tooth rear sprocket. Then should i run sprocket on jackshaft (clutch side) about the same at 14 or should i bump it up to 16 or so. What about sprocket side? like i said i dont really understand how the ratios work. Im just trying to get a ballpark. I can always change the jack shaft sprockets but i would not want to change clutch or rear sprocket.
 
weldkingoc

weldkingoc

Active Member
#4
#4
I mean if i ran 14 on clutch and 14 on jack shaft sprockets that would make all that stuff 1:1 right? so what ratio would a 40 tooth rear and 14 tooth jack shaft sprocket make it, 4 1/2:1 or so?
 
Motra

Motra

Active Member
#5
#5
To get the ratio you divide the driven sprocket teeth by the drive sprocket teeth, 40 divided by 14 is 2.857. That's pretty high gearing, you would want that about doubled. If you go with a 14 clutch to a 40 jackshaft then reduce it to 14 from jackshaft to 40 rear wheel then you have 5.714:1 gearing. That'd work good with a 9HP engine.
 
weldkingoc

weldkingoc

Active Member
#7
#7
ah ok i see. But a 40 sprocket on a jack shaft would be a bit big i would say. Maybe a smaller amount of teeth on clutch if available?
 
Motra

Motra

Active Member
#8
#8
The 5.714:1 gearing would be good for about 30 MPH at 4000 RPM. You could probably go with a 35 tooth jackshaft driven sprocket.
 
Motra

Motra

Active Member
#9
#9
The 35 tooth would be good for about 32 MPH, you could probably go down to a 30 or even a 25 tooth on the jackshaft.
 
weldkingoc

weldkingoc

Active Member
#10
#10
How bout this. CLUTCH = 14 tooth sprocket and related JACKSHAFT sprocket =21 tooth for a ratio of 1 .5:1. then for the REAR sprocket =40 tooth and related jack shaft sprocket 9 tooth for a ratio of 4.44:1. Then add the two for an overall of 5.94:1. Is that how it works.
 
Motra

Motra

Active Member
#12
#12
Yes to your last two posts. Then to get the top speed you divide the engine RPM by the final gear ratio, then that number times drive wheel circumference (I estimated that to be 45"), then that number times 60 (min. in 1 hour), then that number divided by 12 (inches in 1 foot), then that number divided by 5280 (feet in 1 mile). That gives you the top speed. To be totally accurate you should measure the outer circumference of your wheel (fully inflated) because I estimated it to be 45". I also based your top speed on 4000 RPM, your engine might be set at 3600 or you may have disconnected the governor, either way, if you know your engines top RPM then use that number.
 
weldkingoc

weldkingoc

Active Member
#16
#16
So at 5.94:1 with governed rpm at 3600 and a 6" rear wheel with an overall circumference of about 38" top speed will be right around 21. If i gear it higher at 4:1 top speed would be a little over 30 which would be cool as long as its not a slug off the line.
 
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