1st build.
- Thread starter NINETOE
- Start date
Hey Ninetoe,
Here is a handy gear ratio calculator LINK
You just type in the number of teeth on your clutch, the number of teeth on your jackshaft input, the number of teeth on your jackshaft output, and the number of teeth on your rear sprocket. It will then give you your overall ratio.
For your Briggs engine, I would recommend a ratio of between 12:1 and 10:1, depending on how you ride and your topography. If you need to climb steep hills, then you might go more towards a 13:1 or 14:1 ratio, but 16:1 ratio would really limit top speed.
I can not really see how many teeth your different sprockets have, but looking at your pictures, it looks like you may be able to leave the rear sprocket as is and change the INPUT sprocket on the jackshaft. Making this sprocket larger would do the same as making the rear axle sprocket bigger. That output jackshaft sprocket looks pretty small, maybe 10 teeth. Then if the rear sprocket is 40 or so that gives you a 4:1 ratio in the back. If your clutch sprocket is 12, you would need a 30 tooth sprocket to get you to 10:1.
To get the overall ratio you divide rear axle sprocket by output sprocket on jackshaft, that's one ratio. Then you divide the input jackshaft sprocket by the clutch sprocket, that's the other ratio. You then multiply these two ratios to get the overall ratio. 4:1 times 2.5:1 would be 10:1. If you changed the jackshaft input sprocket to 36 in this scenario, you would get a 12:1 ratio.
Hope that helped,
Gilbert
Here is a handy gear ratio calculator LINK
You just type in the number of teeth on your clutch, the number of teeth on your jackshaft input, the number of teeth on your jackshaft output, and the number of teeth on your rear sprocket. It will then give you your overall ratio.
For your Briggs engine, I would recommend a ratio of between 12:1 and 10:1, depending on how you ride and your topography. If you need to climb steep hills, then you might go more towards a 13:1 or 14:1 ratio, but 16:1 ratio would really limit top speed.
I can not really see how many teeth your different sprockets have, but looking at your pictures, it looks like you may be able to leave the rear sprocket as is and change the INPUT sprocket on the jackshaft. Making this sprocket larger would do the same as making the rear axle sprocket bigger. That output jackshaft sprocket looks pretty small, maybe 10 teeth. Then if the rear sprocket is 40 or so that gives you a 4:1 ratio in the back. If your clutch sprocket is 12, you would need a 30 tooth sprocket to get you to 10:1.
To get the overall ratio you divide rear axle sprocket by output sprocket on jackshaft, that's one ratio. Then you divide the input jackshaft sprocket by the clutch sprocket, that's the other ratio. You then multiply these two ratios to get the overall ratio. 4:1 times 2.5:1 would be 10:1. If you changed the jackshaft input sprocket to 36 in this scenario, you would get a 12:1 ratio.
Hope that helped,
Gilbert
THANKS Gbrebes!
I was looking for something like that,as couldn't remember just the right ratio. That is a nice simple chart. 16 to 1 is good for the small 1hp Briggs and this old fart, but 12 to 1 is better for all around ..................Curt
I was looking for something like that,as couldn't remember just the right ratio. That is a nice simple chart. 16 to 1 is good for the small 1hp Briggs and this old fart, but 12 to 1 is better for all around ..................Curt
Ended up with a 32 tooth sprocket .Only took a week to get LOL ! I ended up using the tensioner wheel I got from curtisfox . It worked out well ! Here is it running and Ill try to get its first ride up next.
https://www.youtube.com/watch?v=TPJK4rz4sh4&feature=youtu.be
https://www.youtube.com/watch?v=TPJK4rz4sh4&feature=youtu.be
Heres the first run . It topped out at 29 mph , need a little more out of it though 
https://www.youtube.com/watch?v=ppzQjLpgHio
https://www.youtube.com/watch?v=ppzQjLpgHio
Hey Ninetoe,
I would like to offer help on your gearing. I am still not sure how many teeth are on your clutch, but I will guess 10. If you have 10 clutch, 32 jackshaft input, 10 output jackshaft, and 46 at the axle, that gives you a 14.72 ratio. If you change the jackshaft input to 26, that would give you a 11.96 ratio, just about 12:1. I think this will give you a little more top speed. The bike will take off a little slower though.
Hope this helps
Gilbert
I would like to offer help on your gearing. I am still not sure how many teeth are on your clutch, but I will guess 10. If you have 10 clutch, 32 jackshaft input, 10 output jackshaft, and 46 at the axle, that gives you a 14.72 ratio. If you change the jackshaft input to 26, that would give you a 11.96 ratio, just about 12:1. I think this will give you a little more top speed. The bike will take off a little slower though.
Hope this helps
Gilbert
If you want to change the rear wheel sprocket, you would need to have it be smaller than 44 to get closer to the 12:1 range. This should help your top end speed. If you made the rear sprocket a 38 tooth, that would give you a 12.16 ratio.
Gilbert
Gilbert
You're topping at 30 because 12:1 is too low gearing. I have a 148cc briggs powered schwinn with a two speed and my first gear is 12.2:1, top gear is 7.6:1. I ran with 8:1 single speed for a long time and it was perfect apart from the heavy clutch chatter.
I suggest you go to a 9:1 or 9.5:1. With that ratio you will be turning 4600 rpm at 40mph. Your engine will float the valves around 6k so you might comfortably reach 45mph at around 5200rpm.
Your max torque clutch is going to complain, so consider adding heavy weights and a heavier spring to make engagement smoother. See greaser monkeys thread "max torque clutch tuning mods".
Far as gears, ditch the 10t on the jackshaft and go with an 11 or 12t on the jackshaft. Your final drive chain will last longer. Put a 23t on the jackshaft. I have one right here I'm not using, $10 shipped it's yours (#41). 10-23, 11-44 is 9.2:1. Or keep your setup bit only change the 32 to a 23, that will give a 10.12:1 which is 40mph @ 5250rpm.
The heavier clutch weights and springs can be had from agk.
I suggest you go to a 9:1 or 9.5:1. With that ratio you will be turning 4600 rpm at 40mph. Your engine will float the valves around 6k so you might comfortably reach 45mph at around 5200rpm.
Your max torque clutch is going to complain, so consider adding heavy weights and a heavier spring to make engagement smoother. See greaser monkeys thread "max torque clutch tuning mods".
Far as gears, ditch the 10t on the jackshaft and go with an 11 or 12t on the jackshaft. Your final drive chain will last longer. Put a 23t on the jackshaft. I have one right here I'm not using, $10 shipped it's yours (#41). 10-23, 11-44 is 9.2:1. Or keep your setup bit only change the 32 to a 23, that will give a 10.12:1 which is 40mph @ 5250rpm.
The heavier clutch weights and springs can be had from agk.
Last edited:
One more run in the cold . Will change gears this weekend for a little more top end speed.
https://www.youtube.com/edit?o=U&video_id=HljL-E7CS30
https://www.youtube.com/edit?o=U&video_id=HljL-E7CS30