6kg front wheel (with Bafang BPM 500W) is to much??

[casainho]

Hello.

I am mounting a Bafang BPM 500W on a aluminum fork (a 100€ Suntour suspension) with arm torques. The full wheel weights 6kg and seems a lot me. Will be safe to use this bicycle?

[neptronix]

All that weight sits on the ground. Your bike sits on that wheel. So it is not a problem.

That is a powerful motor, almost as powerful as the MAC/BMC. Your main concern is proper torque arms. A front motor dropout failure is very dangerous.

[casainho]

All that weight sits on the ground. Your bike sits on that wheel. So it is not a problem.

Ok, I understand what you say, but and in the case of jumps/bumps?

That is a powerful motor, almost as powerful as the MAC/BMC. Your main concern is proper torque arms. A front motor dropout failure is very dangerous.

Yes, the dropouts did broke and I jumped over the handle bars, see here my original message: viewtopic.php?f=3&t=35323&start=60#p548462

To say the true, I am afraid to use this motor but at the same time, I like the speed and power it provides, and I am looking to that.

[neptronix]

I am disgusted that nobody recommended torque arms / plates to you. Wow. I could have told you that was going to fail.

During bumps and jumps; same thing. the fork pushes it's force on the hub.

You know what goes wrong? dropouts on bicycles ( front and rear ) are not designed to have a side-to-side twisting motion! They are designed to have an up and down motion only. This is why most people go with rear motors, and torque plates/arms are involved even in the rear.

Think about it - people on this forum use 7-11kG hub motors with motorcycle wheels sometimes - no problems! it's all in the torque arms / plates.

[casainho]

Thank you for your feedback. In 2 days i will receive the BMSBattery arm torque and test them. I will also weld them on a shop.

[Drunkskunk]

Thank you for your feedback. In 2 days i will receive the BMSBattery arm torque and test them. I will also weld them on a shop.

Just about NEVER use a hub motor with an aluminum fork. And in rare cases where it can be done, a geared motor is another big NO, because it generated higher torque on the axle, and twists out of and breaks the aluminum dropouts with even more power. And then abusing it off road adds even more HELL NO, and F**K NO to the equation here.

Its not the weight thats the issue, its the twisting motion and force of the motor against the dropouts that pushes them beyond their limits.

The BMS torque arms are steel. the fork is aluminum. You can't weld steel to aluminum. you could glue it with some industreal structural epoxy, but that hasn't been tried on a front fork, and you got damn lucky with the last break.


Get a steel fork

[dogman]

I'm one of the few that does run a motor on alloy suspension forks.

See me dirt riding it, doing jumps or tricks? Hell no.

Fine for a boring commuter, but not for hard riding.

[casainho]

Before receiving the arms torque from BMSBattery, I were preparing the fork dropouts and the washers. On the disk brake side I don't get room to a torque arm, to say the true, there is even not enough axle for the nut:





And on the other side, I get about 8mm free of axle. Note that since I have space, I am using one of the strong (4mm thick) "C" washers that BMSBattery sent with the motor:




And today I received the BMSBattery arms torque made of stainless steel:






On this side I have enough room for using 2 arms torque. I want to weld them on the local of the screw so they can't rotate on that "joint". Since the wheel will be moving forward, the torque will try to move the axle backwards and so I think this position will be the best since arm torque will be pushing the fork. Maybe I can weld also some bigger piece of metal in the end of arm torque to spread the point of contact/force against the aluminum fork.




And here a picture showing the other side of Bafang BPM 500W motor and not enough axle to hold the torque arm and the nut...


Please give me ideas, your opinion on what would you do on this situation were I have this material: the nuts, washers, arm torque and aluminum fork.

Thank you.

[e-biker]

I would take the advice drunkskunk gave you and get a steel fork!

[casainho]

I would take the advice drunkskunk gave you and get a steel fork!

Could be, but since I got my 2nd fork broken, I go now with rear motor.