I am considering a cheap Schwinn bike for my next ebike. I have narrowed it down to a couple of choices, both with steel front forks. My concern is that I occasionaly read on this, and other forums, that front forks with suspension are not recommended for front hub motors. What is the reason for this? It would seem to me that if the forks are steel and you provide enough slack so your wiring cannot be pulled out, that front suspension would be alright. What am I missing? Thanks for any input. Tony
Front suspension is it a problem?
- Thread starter nb141fd
- Start date
Sacman
10 kW
nb141fd said:
Front forks with suspension are designed to take compression loads that are axial (or in-line) with the shocks. Picture this... If you tie a rope to your bike's front axle and tied the other end to the rear bumper of a car. Now imagine that you are sitting on your bike and someone drives off in that car. The rope is going to put a TENSION LOAD on your front suspension forks that is SIDEWAYS or non-axial to the shocks. It will literally yank really hard sideways on the shocks.The shocks on your front forks were NOT designed for LARGE sideways tension loads. But that's precisely the load that you put on the forks when you put a front hub motor on it.
I definitely would not put a front hub motor on a cheap bike (from WalMart) with cheap suspension forks. I would only try it on a stronger, higher quality front suspension fork.
Tiberius
10 kW
There are production electric bikes with front hub motors and suspension forks, but they are quite probably non-standard forks.
I'm not so sure about the longitudinal load issue: far larger forces are generated during braking than from the motor.
One reason people caution about mixing front hub motors and suspension forks is the problem of axle width. Quite often the hub motor is wider than standard front wheel hubs. With non-suspension forks it is possible to just spread the forks a little, but with suspension forks this can stop the suspension working.
Nick
I'm not so sure about the longitudinal load issue: far larger forces are generated during braking than from the motor.
One reason people caution about mixing front hub motors and suspension forks is the problem of axle width. Quite often the hub motor is wider than standard front wheel hubs. With non-suspension forks it is possible to just spread the forks a little, but with suspension forks this can stop the suspension working.
Nick
dogman dan
1 PW
Again on this thread. Over 1000 miles on cheap steel suspension forks with a WE BD36 hub. No problems. I ride 25mph and hit the bumps hard enough to get some air. Aluminum forks, forget it. The only problem is clearance but there is nothing but tubing in the bottom 4 inches of these cheap forks, so you can just squash em in a vise to make clearance. There is a thread on it buried here somwhere in either ebike tech, or general. You can't squash enough space to fit an x5 motor, but for a small one there is. The forks are dogs, with 40 mm of travel, but it's good enough for street commuting. For dirt riding, get a rear hub so you can use nice forks.
You can definitely see the forks flexing under the longitudinal load, but at 1000 miles, I see no more flexing than when new. They flex twice as much when braking than when the motor pulls. Just don't ignore it if the flexing starts increasing. These are cheezy forks for sure, but weak they are not.
You can definitely see the forks flexing under the longitudinal load, but at 1000 miles, I see no more flexing than when new. They flex twice as much when braking than when the motor pulls. Just don't ignore it if the flexing starts increasing. These are cheezy forks for sure, but weak they are not.
RLT
10 kW
The cheap 5 year old old Walmart Mongoose full suspension bike I built my 2WD on has pretty strong steel front suspension, and has managed not to break, even off road, despite total bike and rider weight being 350 pounds. Not that I ride as aggressively as BMXers or Downhillers. But I do pull up to 2800 watts through that front motor.
That's not to say that it won't break sometime in the future, but so far so good. I do have faith in it.
Not so for the new super cheapie Walmart "Roadmaster" front suspension 'comfort' bike I bought there last month for a 'test bed'... I won't be hanging a motor on those forks.
But a few caveats: since it is two wheel drive, with the rear pushing, there is generally a lot less torque on the front end than if it were just the front motor pulling. And my home made torque arms were designed to help to reinforce the lower suspension tubes. But I don't think I'd hesitate to run a front hub motor system limited to somewhere under a thousand watts on the older Mongoose front forks, even without the rear motor... In fact, I have done so, for a few miles of cautious on and off road riding when I first started the build.
If you use good judgment in building AND riding, and good torque arms, you don't have to rule out putting a 'legal wattage' hub motor on a decent pair of steel suspension forks.
I'd refer you to this as well:
http://www.electricrider.com/crystalyte/hubfaq.htm#Can%20I%20use%20a%20front%20wheel%20motor%20with%20a%20suspension%20fork?
That's not to say that it won't break sometime in the future, but so far so good. I do have faith in it.
Not so for the new super cheapie Walmart "Roadmaster" front suspension 'comfort' bike I bought there last month for a 'test bed'... I won't be hanging a motor on those forks.
But a few caveats: since it is two wheel drive, with the rear pushing, there is generally a lot less torque on the front end than if it were just the front motor pulling. And my home made torque arms were designed to help to reinforce the lower suspension tubes. But I don't think I'd hesitate to run a front hub motor system limited to somewhere under a thousand watts on the older Mongoose front forks, even without the rear motor... In fact, I have done so, for a few miles of cautious on and off road riding when I first started the build.
If you use good judgment in building AND riding, and good torque arms, you don't have to rule out putting a 'legal wattage' hub motor on a decent pair of steel suspension forks.
I'd refer you to this as well:
http://www.electricrider.com/crystalyte/hubfaq.htm#Can%20I%20use%20a%20front%20wheel%20motor%20with%20a%20suspension%20fork?
totals
10 mW
I ride a 5303 on front suspension forks. I read alot about the risks, but so far, I haven't had a problem. I would just recommend that they are steel... alumium snaps easier, and without warning.
Rory
Rory
No doubt, safety straps or torque arms in place in case of failure for aluminum dropouts. I have a forged (hoping :| ) aluminum crown with steel steerer tube and stanchions. The crown would be the only danger if there is one. The whole fork flexes quite a bit with 100mm travel. Its tall. I would of rather had 80mm but those don't come with the steel tubes. Got about 1500 miles on my fork with 408 hub motor.
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