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Shaft drive?

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Don't laugh. 

What would be a disadvantage to shaft drive on a dirt bike? Just weight?

I'm a very accomplished fabricator, and I might be getting an 80's Fourtrax 250 in a trade. I can't help but let my mind wander to the dark unknown... purchasing an old shaft drive street bike for the back half of the drive, and fitting it all into a bike frame, creating a Fat Cat-esque utility bike. It would be an e-start, auto clutch bear of a bike (with reverse!) for taking out in the spring to clear trail, or dragging crap around our property.

Thoughts? Am I missing something? Has this ever been approached before?

Edited by ITLKSEZ

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I'd say weight, strength and torque reaction would all be issues.

Shaftie street bikes (at least the ones I've ridden/owned) have terrible torque reaction, the rear goes up and down like...well.... you know what.....they also run through a fairly small universal joint, which is weaker when on a big angle (like a long travel dirt bike would do) and weigh a ton. And the rear hub is a big part of it, so lotsa unsprung weight too.

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12 hours ago, ITLKSEZ said:

Don't laugh. 

What would be a disadvantage to shaft drive on a dirt bike? Just weight?

I'm a very accomplished fabricator, and I might be getting an 80's Fourtrax 250 in a trade. I can't help but let my mind wander to the dark unknown... purchasing an old shaft drive street bike for the back half of the drive, and fitting it all into a bike frame, creating a Fat Cat-esque utility bike. It would be an e-start, auto clutch bear of a bike (with reverse!) for taking out in the spring to clear trail, or dragging crap around our property.

Thoughts? Am I missing something? Has this ever been approached before?

I think you also need to ask what the advantage of a shaft drive would be... I can't see one. If you're just looking for a cool unique project to get into, have at it. But if you're looking to build something practical and usable, I don't think this is it. Would be a fun project to goof around with tho

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10% power loss?? Really? Is that proven? Why do they use them then? Just for lack of maintenance?

 

I've been wanting to build something like this for a long time. The essence of a workhorse utility quad, but on two wheels. Like a 1wd Rokon with suspension and more versatility. Something with low COG and high flotation to travel over spring snow berms to get an early start on mountain trail clearing. Smaller than a BW350, and with auto clutch and reverse.

We live on 6 acres of treed mountainside that will flip anything that has more than two wheels if you attempt anything other than straight up or down. When a tree dies, I'm rolling it out piece by piece, and I'm getting too old for that crap. 

The quad I'd get in this trade runs, but the rear axle is broken. I'd consider shaft drive for this project for no other reason than it's virtually free and it would be interesting. I'm sure I'd end up rebuilding the rear drive to have a longer swingarm and beefier u-joints if possible, but we'll see. It might be more practical to part it out to fund a more practical base drivetrain. The one I've always envisioned for this project would have low range too. I'll check it out when I get it and see if it's worth the trouble. 

Thanks for your input guys.  

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On a large touring bike, a 10% loss would never be noticed as the riders rarely use even 30% of available power. On these bikes, the name of the game is long distance. A chain wears, is noisy, requires maintenance. So a shaft is the way to go. A belt is inexpensive,  pretty maintenance free, retains the power and is pretty quiet but, once they fail, you are stranded and replacement is often a massive job. Neither a chain or a belt survive well in harsh conditions.

So on a workhorse quad, where speeds are relatively low, the power loss of a shaft is more than compensated for by the durability. The ROKON chain drive is enclosed in a case (real old skool) with an oil bath.

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