Homemade minibike gear ratio

[Cotmullion]

I've been building a minbike from scratch. I've used a 2.5hp 100cc cylinder mower engine and a frame which I built myself. It is clutchless (push start) and has two 10 inch pnuematic wheels. The gear ratio is 9 on drive, 26 on axle, so about 3:1. Is this OK?

 

[jr dragster T]

It's ok if you want it to bog ALOT and then go 50 MPH. You need a MUCH larger sprocket on your axle. You want around a 6:1 ratio. For example, I have a 12 tooth on my torque converter and a 72 tooth on my axle. With this gear ratio setup and a TAV 2 30 torque converter I have mega torque.

 

[crazycart]

I agree with tyler especially because its a direct drive and no way in hell would i want to be going that fast with it lol...

 

[Cotmullion]

It is calcuated to go at about 16-20mph. Is that too fast?

 

[jr dragster T]

No thats pretty slow atually. Hard to belive that with that kind of ratio and 3600 RPM and your tire size it calculates out to 16-20 mph?

 

[Cotmullion]

I believe the RPM is 1800 to 2000.

 

[Kenny_McCormic]

If its only going that high something is wrong or you have a old engine worth serious dough. Is it governed?

 

[Cotmullion]

I just heard that engines like this had about 1800 to 2000. I haven't measued the RPM myself. Does 1800 not sound right?

 

[crazycart]

1800 is like idle speed. What kind of engine is this?

 

[jr dragster T]

1800 is like idle speed. What kind of engine is this?

What you mean not all you guys idle your engine at 3000+

And most engines top out at 3600 RPM on the governer.

 

[crazycart]

Most Engines? Mostly just the little flathead and ohv 5 hp's and up...the "Utility engines" My trikes 4 stroke 400 redlines at around 12,000 RPM.

 

[jr dragster T]

Ohh sorry I ment most small engines. My JR runs 9 grand at the top end of the track.

 

[crazycart]

Hey tyler, just wondering what CC that engine is?

 

[jr dragster T]

It's around 350+. But cc's is nothing realy when running this many performance parts.

 

[crazycart]

Yeah i know i was just wondering...

 

[jr dragster T]

Cool Cool..Its a 3 inch stroke and a 3 5/16 bore.

 

[Cotmullion]

1800 is like idle speed. What kind of engine is this?

It's a Qualcast 98cc cylinder mower engine. I the whole mower for 15 pounds.

 

[crazycart]

2 stroke, 4 stroke?

 

[Cotmullion]

http://www.cotmullion.com

4 stroke. Read about all my projects, including my homemade minibike, at the website above.

 

[oscaryu1]

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