[pengyou]

to be used as a donor to make an ebike? I am thinking of installing a motor w/chain drive on the front fork so will consider some form of steel - maybe chromoly (not too expensive but still strong and is easier to weld onto). I want to find an aluminum mountain bike frame with a rear suspension to try to shave a few pounds off the total weight of the bike. My concern is that, when all is said and done, I will have 3 sets of li-on batteries, a 6 pound motor, a 2 pound controller on the bike in addition to the weight of the bike itself, as well as a second rider on the back...and I will be on this bike sometimes as long as 7 hours at a time.

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[Abneycat]

You're talking about a bike mounted motor driving the front wheel with a chain drive? I've personally never heard of that before. The front fork is really not made to handle torque, and most drives will exceed its tolerance unless its a solid steel non-suspension fork, so your steel fork is a good consideration for sure. Remember that if your rear wheel fails, usually the worst result is that your bike may be broken. If your front wheel gives out when you're riding, you flip. Hard, fast and brutal.

My concern would be that if you're having a second rider on the back of the bike, no aluminum bike would really be able to handle that plus the weight of your gear. Aluminum might be stiff and light, but if you go over a bump and exceed its tolerance, it will crack or bend. That won't take long to turn into something nasty.. You might want to look at basing your bike off of a Clydesdale.

[AllenG]

Trying to power the front wheel with a chain drive is not practicable.

An Al frame can handle a deal of weight though. I've got well over 10k miles on this set-up and have overloaded it regularly. Steel would last longer, but I've gotten a very useful life from this frame.
http://homepage.mac.com/awcg/.Pictures/Bike/Giant/XtraGiant.jpg

[Abneycat]

Trying to power the front wheel with a chain drive is not practicable.

An Al frame can handle a deal of weight though. I've got well over 10k miles on this set-up and have overloaded it regularly. Steel would last longer, but I've gotten a very useful life from this frame.
http://homepage.mac.com/awcg/.Pictures/Bike/Giant/XtraGiant.jpg

That looks like it would handle the load really well, but it also looks very purpose built. I'm not saying you couldn't build an aluminum frame for that purpose because you definetly could, but i'd be skeptical about taking a normal aluminum mountain bike frame and refitting it for a passenger. I think the average aluminum frame is designed to carry about 230lbs. Its not the static weight thats the concern, it would be how the aluminum would handle the load dynamically over time after going over bumps and such.

I really have to agree, powering the front wheel with a hub is good for some applications, but using a chain honestly seems like an odd idea. Considering that front wheels are usually tight fit into the fork, how would you attach the chain drive? Where would the motor sit?

P.S. that looks like a really nice bike, AllenG.

[AllenG]

Thanks Abney,
I've gotten a lot of use out of it. It's a Giant Lite/Twist with a long tail kit added.
I would expect an Al mountain bike would handle the load if one used a properly engineered extension. However this is the only Al frame I have. Agreed--I don't really care for the metal fatigue properties of aluminum either.

[meb]

Trying to power the front wheel with a chain drive is not practicable.

An Al frame can handle a deal of weight though. I've got well over 10k miles on this set-up and have overloaded it regularly. Steel would last longer, but I've gotten a very useful life from this frame.
http://homepage.mac.com/awcg/.Pictures/Bike/Giant/XtraGiant.jpg

The Currie E-trikes had a chain front wheel drive approach, so it is doable.

[pengyou]

Thanks for your thoughtful responses. I have a common ebike in China now. This whole idea started coming about when I was lamenting the ability to pedal my bike - I mean really pedal. The pedals on my ebikes are designed to get the bike to about 2 km per hour to take the stress of getting the bike going off the motor. When I am riding outside of the congested areas of town I really wish I could stretch my legs. It looks like steel...I think the difference will only be 5 pounds or so, so that doesn't matter. I have gone back and forth with the motor on the front wheel vs. mounting the wheel near the crank and finding a way to add a freewheel. I like the idea of spreading the weight out a little bit, even pushing some of it up front. The motor, mounting bracket and chain should add about 8 pounds to the front fork. I know a belt would be quieter.

[JeanCoutu]

The Currie E-trikes had a chain front wheel drive approach, so it is doable.

+1, I've crossed a so-equipped trike a few months ago.

If I recall properly, Scott at EVdeals (http://www.evdeals.com/) knows how to make a Currie fit on a front wheel.