Electric Bikes - bike frame structure integrity?

hi...
i once got something similar to these bikes
http://www.greenwheels.co.il/bikes/large/kor002.jpg

which have 250watt engine and can go up to 20kph on the lowest gear.

i'm considering upgrading my "regualr" bike which are trek 7300 model with a 500 watt engine (same structure as the 250watt) and 2 batteries.
according to my calculations considering that the engine on the folding gives me around 5-6 kph boost the new engine on the new bike should go around 30-35 kph on the lowest gear.

however i was warend ,the bike frame was not designed to have such a stress of this speed, and that it have fractures, during regular use, not to mention shock absorbents failures.

is this true?

I don't know what a Trek 7300 bike looks like but if it is as you say "a regular bike" then it will be fine. 35kph is not fast in the ebike world. However, if the motor is a hub drive motor you should add a torque arm to the drop out especially if it is a front motor.

Bob

http://www.trekbikes.com/images/bikes/2011/xl/7300_bluesilver.jpg
and as you can see from the former image the motor is a chain motor.
they talked abotu how keeping a constant 35kph or more is not suited for such bikes.


I don't know what a Trek 7300 bike looks like but if it is as you say "a regular bike" then it will be fine. 35kph is not fast in the ebike world. However, if the motor is a hub drive motor you should add a torque arm to the drop out especially if it is a front motor.

Bob

hi...
i once got something similar to these bikes
http://www.greenwheels.co.il/bikes/large/kor002.jpg

which have 250watt engine and can go up to 20kph on the lowest gear.

i'm considering upgrading my "regualr" bike which are trek 7300 model with a 500 watt engine (same structure as the 250watt) and 2 batteries.
according to my calculations considering that the engine on the folding gives me around 5-6 kph boost the new engine on the new bike should go around 30-35 kph on the lowest gear.

however i was warend ,the bike frame was not designed to have such a stress of this speed, and that it have fractures, during regular use, not to mention shock absorbents failures.

is this true?

I personally think that if you were told the bike wasn`t designed for it ,.... I think you should listen.

Thats a hybrid designed for city driving and the OCASSIONAL trip out loaded for a picnic. Yeah - it would even be OK to pull a trailer (kids trailer). Hybrids weigh in around 24lbs.

But people don`t drive hybrids at average speeds over 20kph - thats a fact. Mostly its leasurely driving on bicycle trails, even more so with a trailer attached.

OK - lets look at touring bikes. There the frames are STRONGER in anticipation of carrying more weight on a regular basis. As a result, touring bikes usually weigh in around 30lbs. But a touring bike doesn`t average 30kph loaded either.

So lets consider some pecularities of electric bikes in `kitsl. Aside from a motor, there`s a battery that normally requires a rack. In most cases that ends up over the rear wheel. If your motor is also in the rear, thats even more weight in the back.

Weight distribution is important to stability and touring bikes loaded are recommended to do a 60/40 front/back weight distribution and keep the centre of gravity as low as possible.

So all this helps explain why dedicated electric bikes like Velec,arguably the best e-bike in Canada, is built with a centrally located battery, oversized tubing, heavy duty rims and comes with a front suspension system. A computer controlled limiter restricts the top speed to just over 30kph because thats the legal limit for e-bikes here. But it`ll do that against a bit of a headwind and is covered by an extensive warranty program.

So althought you might be able to put together something `functional` with a kit and a hybrid, it wouldn`t be stable and you would void the warranty on the frame.

Personally if I was to put together an e-bike using a kit, I`d start with a mtb bike. And not just any model. It would have to be a frame designed for dirt jump. That would be strong enough to handle the additional stress and would have a decent front suspension.

becouse i carry my 100kg on them, so the 5kg addition of the engine and battery shoudln't matter much.
however i do agree about the distribution, that's why i've enclosed a picture of the kit, as you can see this is a chain engine, and battery is also located instead of water cage (and on the hybrid it could also be placed horizontally..
currently i' chose the standard 250 watt, but they have trouble mounting the engine on them (they need better, the central axis seems rather complex to them) as well they are currently unable to remove the peddle.s


I personally think that if you were told the bike wasn`t designed for it ,.... I think you should listen.

Thats a hybrid designed for city driving and the OCASSIONAL trip out loaded for a picnic. Yeah - it would even be OK to pull a trailer (kids trailer). Hybrids weigh in around 24lbs.

But people don`t drive hybrids at average speeds over 20kph - thats a fact. Mostly its leasurely driving on bicycle trails, even more so with a trailer attached.

OK - lets look at touring bikes. There the frames are STRONGER in anticipation of carrying more weight on a regular basis. As a result, touring bikes usually weigh in around 30lbs. But a touring bike doesn`t average 30kph loaded either.

So lets consider some pecularities of electric bikes in `kitsl. Aside from a motor, there`s a battery that normally requires a rack. In most cases that ends up over the rear wheel. If your motor is also in the rear, thats even more weight in the back.

Weight distribution is important to stability and touring bikes loaded are recommended to do a 60/40 front/back weight distribution and keep the centre of gravity as low as possible.

So all this helps explain why dedicated electric bikes like Velec,arguably the best e-bike in Canada, is built with a centrally located battery, oversized tubing, heavy duty rims and comes with a front suspension system. A computer controlled limiter restricts the top speed to just over 30kph because thats the legal limit for e-bikes here. But it`ll do that against a bit of a headwind and is covered by an extensive warranty program.

So althought you might be able to put together something `functional` with a kit and a hybrid, it wouldn`t be stable and you would void the warranty on the frame.

Personally if I was to put together an e-bike using a kit, I`d start with a mtb bike. And not just any model. It would have to be a frame designed for dirt jump. That would be strong enough to handle the additional stress and would have a decent front suspension.

I recently started an E-Bike build. I thought finding the bike frame was going to be easy, but in the end, it turned out to be the hardest thing to find.

Perhaps I'm a little picky, as this is my second E-Bike build, and I don't want to repeat the mistakes I made on my first build. But I ended up looking at many bike frames, and I was shocked at how thin the metal was on many of the frames I saw.

BTW, most of the drop outs on the front forks of mountain bikes... (With the shocks) Are aluminum. Do not mount a motor in the front wheel of a bike with Aluminum crowns. Even with Torque arms its dangerous.

Cast steel, or alloy will flex when stressed, but the cast Aluminum crowns won't flex, they will shatter like glass. Mount the motor in the back if at all possible. (If we are talking about hub motors)

190523
^^ The frame I ended up with after the search.

this is not a hub motor, look at the first picture, it's chain one.