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gear ratio

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gear ratio

Unread postAuthor: jon_89 » Thu Aug 23, 2007 12:12 am

ok so i am making a gas scooter using a a razor kick scooter and a 22cc weedeater motor. i was wondering what a good gear ratio would be for this. i need to go up some pretty steep hills so i need a lot of low end power but i also need a little bit of speed somewhere around 15 mph. i have looked on tzi's website and everybody seems to have different ideas. does it matter whether the bigger sprocket is on the motor or the wheel? thanks
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Unread postAuthor: hi » Thu Aug 23, 2007 12:24 am

well yes it matters whether the big sproket is on the motor or wheel.

if the motor has the big sproket the scooter will go very fast, but if the motor has the little sproket it will have lots of power. its simple, big wheels give you speed, little wheels give you power.

if i were you i would go for power, that way you would never have to wory about stalling or anything like that, but thats just me. id be willing to bet that even with a low gear ratio you could still get 15 mph because most schooters can get up to about 35 mph or so.

have never built a scooter, so i cant give you a good ratio, but i can tell you what i just did. :wink:

i do have a problem with you using a little razor though. i simply dont think that little thing can take the abuse of a engine on it. it has very very small wheels that are about 1/3 the size of normal scooters. also, weed eater engines arent exactly the smothest running engines in existance, they tend to vibrate alot and that will probably just shake the schooter apart overe time.

maybe im worring about things that dont matter, i just think you need bigger wheels and a stronger heavier frame.
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Unread postAuthor: jon_89 » Thu Aug 23, 2007 12:31 am

so if i put the bigger sprocket on the wheel i have better hill climbing abilities?
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Unread postAuthor: hi » Thu Aug 23, 2007 12:39 am

yes.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: jon_89 » Thu Aug 23, 2007 12:46 am

do you know of a simple way to change between 2 gears like a high and a low?
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Unread postAuthor: hi » Thu Aug 23, 2007 1:07 am

again, ive never built anything like this, but maybe you could take the gear changer thing off of a mountain bike. its this little thing that simply pushes the chain over.

the problem might be that a schooter chain spins alot faster than a bike chain.

other than that, no, not simply or weight efficiant.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

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Unread postAuthor: silverdooty » Thu Aug 23, 2007 5:43 am

your better off picking a gear ratio that is somehere in the middle. if you are going to go up small hills you might want one that is a little lower end than one that is top end. that would mean a larger cog on the rear than the motor.
in singlespeed mountain biking the optimal gear ratios are between 2:1 - 1.6:1.

checkout sheldon brown's gear info

http://sheldonbrown.com/gears/

BTW: the gear changer thing is called a derailleur
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