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Old 12-06-2008, 11:56 AM
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Dan Dan is offline
Join Date: May 2008
Location: Moosylvania
Posts: 11,850
Default Re: Need mental and ratio help! Please!

Originally Posted by Ghost0 View Post
Good job on getting it figured out. I always try to not over complicate things. When I was designing the SBP Shift Kit, I figured the manufacture knew what they were doing. The China kits come with a 44 tooth sprocket amd has a 10 tooth output sprocket on the engine. So that is 4.4 to 1. That seemed like a good middle gear. So I just figured if I could get the final drive ratio to be the same on the middle sprocket of the rear cassette I would be in the ball park. I then had both lower and taller gears on the cassette. That way I didn't need to worry about the internal gear reduction, engine RPM, wheel size etc. So the same could apply here. If the Titan has an output sprocket of a 10 and the kit comes with a 50 then I would know that I would need to keep the overall drive at around 5 to 1. Now that I am designing the one for the 4 stroke kit I am using the same principal. And thanks to the Grubee and JL gear reductions they kindly have a 10 tooth output sprocket so the gearing will be the same.
Ghost0, I have been wondering about this. The stock 44T part. I completely agree with you that it is always best to go with the original engineer's thinking and not over complicate things. But I had always wondered why a rear 44T stock sprocket when it would top out a ChinaGirl at 30 MPH rather then make it cruising speed. I think it was Andy who first said that one tooth was about 1 MPH. (Yes Andy? forgive me if I misquoted you as I can not find the post) Dax suggested a 40 tooth which seems perfect for cruising closer to 30 MPH comfortably. So what I am thinking is that the producers of kit engines went with 20 MPH to be the middle ground and adhere to federal law. This all is a question not a suggestion. Where I live the speed limit for a motorized bicycle is 30, so I am aiming for a top speed of 40 MPH for just that reason.

Not questioning you but rather my own thinking.
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