Maro

My intention is to put a front electric motor on an old Miele CrMo road bike that sit unused in the garage.

I am afraid the the bike may not handle the additional stress: it is quite light for an iron frame, and it can only take 700 x 25C tires.

I do not care if I kill the bike, will make space for one more bike, but I do care if I kill or injure myself.

What the worst that will happen with this setup? Can the bike explode at 30MPH?

I intend to go with a not so big motor and battery, and just try it on paved roads.
Any mechanical engineer to help?

Thanks in advance for your advice.

Azreal911

if it's an old bike I would go with a rear motor cause the front forks might be old and would be too much stress on it they're built thinner than mtn bikes.

The worst that could happen is if the front fork snaps from the stress of the motor and you do a face plant at 20-30 mph. Think of the road rash that would do to you. The rear triangle would have alot more supports and could easily handle the extra power you are putting on it.

Maro

If I go with rear motor, would not be too much weight on the back of the bike: motor, batteries, and me?

Azreal911

it should handle you unless yer 300lbs or so. what's an extra 30-40lbs? people gain that much weight in a year. Also you yourself aren't exactly sitting right over the read wheel but more inbetween it. So it shouldn't flip over or anything like those cartoons.

Maro

When I look at the very small diameter seat stays, they look just glued to the seat tube, not welded... It does look very nice, but...
I see your point, though. When the rear wheel accelerates, the force is ALONGSIDE the the chain stays. When the front wheel accelerates, the force try to bend the fork.

SeizeTech

I think an old cromoly road bike would be a very fun electric bike.

I dont personally think that the forces delivered by a front hub motor are severe enough to cause strain on your front fork......

but instead of speculating on this from a mere opinion, why dont you do some math? or use a bit of scientific method for determining the forces that your bike fork will experience.

Here's my idea:

place a bathroom scale between the front tire and a wall, and crank that throttle to see what type of force you motor and battery can put against the scale.

then dig up a mathematical formula for calculating torque, I think its something like Torque = force times distance.

caculate the amount of torque that is happening at the front fork stem.

now go out to a yard sale, and buy a cheap road bike with a steal or cromoly steel fork

apply the caculated torque to the front fork on the cheapo bike......i'll bet it doesnt break or damage

now deliberately break or damage the cheapo fork, while trying to measure the torque.....i'll bet its significantly more than your calculated torqued.

Final step:

look at everything you did, and the numbers that you created and measured......now make a speculated decision on whether you think your idea is safe.

best of wishes to you

ST

hillzofvalp

I, too, am interested in fitting my '95 road bike with electric gear. Since mine will be for fun, primarily, I don't need a ton of capacity. That's why I'm going to try to use 26650 cells, half of which may even fit perfectly in the seat tube (others might go in water bottle). They are 2.3Ah A123 cells. they pack quite a punch. I'm not sure which motor to go with though. The extra front rim I have sure is tempting me to build up a matching front electric hub wheel. I have some links in my thread to another guy who did something similar with his road bike.

Mine is chromoly too, and it's a light race frame (4.1 pounds frame/fork). This is another reason why the A123 cells will work well. At 70g a cell in a 8s2p pack, my bike would be less than 4 lbs heavier plus hopefully less than 15 pounds for the motor/controller setup. I'm almost 200 pounds so I want to keep it at a minimum.