Don't Use Aluminum Forks with front hub motors!

[casainho]

So it's definitely a compromise. It's good within a certain envelope, and bad out side the limits. It works good for me for riding on dry pavement, or wet that is not too steep. It's no good for dirt riding, trail riding. You just gotta have a rear hub for that. Dual hub can be nice in dirt, but really I prefer to have a light front so I can pull a small wheelie over larger obstacles. I run 1200w max, 48v. So I burn a little bit of front tire rubber, but nothing that alarms me. You should get quickly used to a small wheel spin the first foot or so as you start. Do be cautious about going from 0 throttle to full on a corner with wet or sand. But if you are already spun up, you can power through a corner fine.

Ok, it's decided. I will go with the Bafang BPM 500W front motor on aluminum forks but using 2 arm torques.

My travel is 50km (25km + 25km to return) on flat dry pavement/tarmac roads (I live near the ocean). 2 years ago I did this with 180W front motor, 1 year after with 250W front motor and now I want to go with the Bafang 500W.

My controller gives 22A at 48V, which is 1056W at start. Since I came from a 250W motor and I just need more 50 or 100W, I will do 2 things:
- limit the maximum throttle with a circuit to 0.7, 500W*.7 = 350W
- ramp up the acceleration of throttle with the opamp circuit(or Arduino) to have 3 seconds of ramp from 0 to maximum power

Limiting the power to 350W to be safe, also because I don't have gears to go over 44km/h (maximum speed with the 250W motor were 38km/h) and I want to always pedal, also I will ride 50km with a charge but I plan to increase for the 70km/h.
I wish I could limit the power and ramp up on the controller, so when lifting to the air the wheel like on a bump, the wheel would take time to accelerate and so more safe.

I hope to survive to any possible accident due to front motor and have the chance to change for rear motor

My actual electric bicycle is this one (V2.1 in Portuguese):

It is a Cute-85 motor for 16'' but installed on a 26'' wheel, 250W, 24V. Battery 24V 25Ah.

 

[amigafan2003]

This carbon fork with alloy dropouts and a front motor will make many of you cringe then

Just passed 1000 miles on it.

 

[casainho]

This carbon fork with alloy dropouts and a front motor will make many of you cringe then

Just passed 1000 miles on it.

You are pushing your luck by not using arm torque. You don't know if you are near the limit.

 

[dogman dan]

It would make me cringe if it had any power. Properly installed, nut torque alone is proven to provide enough resistance for lower torque levels. And I do see a torque arm.

One thing to note, Sometimes the wider width at the cover common with gearmotors will not fit between the tubes of a suspension fork. You need the type of fork that has the dropouts mounted to the inside of the tube. Many forks have the dropouts centered on the fork tube, and typically the motor cover is too wide to fit. Usually a 9 continent dd motor will fit most forks. It's narrower at the cover, but sometimes still rubs on the bearing housing of a tight fork.

So measure it before you order.

 

[casainho]

It would make me cringe if it had any power. Properly installed, nut torque alone is proven to provide enough resistance for lower torque levels. And I do see a torque arm.

Sorry for my mistake amigafan2003, now I see you are using torque arm.

One thing to note, Sometimes the wider width at the cover common with gearmotors will not fit between the tubes of a suspension fork. You need the type of fork that has the dropouts mounted to the inside of the tube. Many forks have the dropouts centered on the fork tube, and typically the motor cover is too wide to fit. Usually a 9 continent dd motor will fit most forks. It's narrower at the cover, but sometimes still rubs on the bearing housing of a tight fork.

So measure it before you order.

dogman, thank you for sharing. Are you suggestion me to measure before order? If so, I already ordered 2 pairs of BMSBattery arm torque and a KU93 controller (current is KU123, the one that broke the alu dropouts).
I don't know if BMSBattery arm torque are good and if they will work, but before ordering I were ready to make myself them so I will verify and think the BMSBattery ones and if needed weld them or the steel sheet I will use.

 

[dogman dan]

I was talking about measuring the motor itself. Moot point if you have it already and it fits. Depending on the fork design, some motors are too wide for the forks. The dropout is still standard 100mm, but the measure between the two tubes might be only 80 mm. So the motor won't fit between the two tubes.

 

[amberwolf]

Sometimes the wider width at the cover common with gearmotors will not fit between the tubes of a suspension fork.

Yes, the first Fusin I got from you fit fine on DayGlo Avenger's cheap RST Omni fork. But the cover fasteners on it were domed phillips screws, and those on a second Fusin from you were taller squared-profile allen-head bolts, which would only fit if I took the lockwashers out, on one side. Why they fit on the other side I dunno, but they cleared fine there. :?

So even the very "same" motor from the same company may not always fit! And it might not be obvious why it doesn't fit at first, either. The Fusin was obvious, as it clicked on each bolthead. What wasn't obvious at first was that the suspension would "stick" once it went down, and not rebound, so the next bump wasn't absorbed as well or at all, with the spacer in there. Eventually it wore inside the fork enough to work normally again, probably less than a hundred miles.

 

[amigafan2003]

This carbon fork with alloy dropouts and a front motor will make many of you cringe then

Just passed 1000 miles on it.

You are pushing your luck by not using arm torque. You don't know if you are near the limit.

I am using a torque arm - look closer

EDIT: I see you've noticed

It would make me cringe if it had any power. Properly installed, nut torque alone is proven to provide enough resistance for lower torque levels. And I do see a torque arm.

Yeah, it's only pulling 750w max.

 

[mike46]

I snapped the aluminum drop outs on my forks with an Ebike motor coasting a hill, The forks just dug into the ground, crazy stuff
This stuff can be dangerous I only use the steel ones now, but you go to get a new frame, or forks that match to your alum frame.

Do these adapters really work?

 

[dogman dan]

You need to be a bit more specific. Adapter? adapt fork to frame? I'm confused what you are talking about.

 

[OptimusPrime]

If anything, reading this thread leads to the conclusion that Mid-drive is the way to go.

 

[dogman dan]

Or just install hub motors correctly.

 

[Tiggerink]

Don't ever use aluminum forks with a 1200 watt front e-bike motor. I just broke my second set of forks. Fortunately I wasn't going fast either time. I had a torque on securely mounted on BOTH sides of my front fork the second time and it busted on both sides of the fork. ******ONLY USE STEEL FRONT FORKS, ALWAYS AND FOREVER!!! ******
Oh, and also before I forget, never use aluminum forks, ALWAYS USE STEEL FORKS WITH FRONT WHEEL EBIKE KITS!!!

 

[LewTwo]

Or just install hub motors correctly.

AMEN

 

[Manbeer]

I've done a couple aluminum forks just because it was all I had at the time. I would conclude that in general it's not ideal but I would say also very install dependent and dependent on the quality of the fork and design of the dropouts

First one I did was on a cheaper JUDY TT Then I rushed to get done and didn't perfectly notch the dropouts. After using it, re-tightening a few times I still noticed that I was starting to get what looked like inevitable spin out So I got rid of that fork

Next up was a Marzocchi Bomber. Construction was slightly more stout And after retorquing And a decent improvised torque arm I marked the axle nut in the fork with a permanent marker to see if there was any movement and it stayed in the same position for the 5 or 600 miles I rode it.

Eventually, the heavy motor yanking up and down on the suspension just made the ride like such shite i shelved it.

As far as I'm concerned it's a few things. In general the dropouts, it's really also a matter of how well and tightly you fit them. Tiny bit of play and you'll ruin the fork and maybe your face in a hurry

next up the construction of the fork, I am biased against suntour and a lot of cheap forks. I would say that most of the better brands will probably be somewhat more stout. Eventually you will run into the issue of wearing out the bushings because of the constant back-and-forth tugging of acceleration and braking

Aluminum Rigid fork that you take your time on With a proper torque arm set up would probably be somewhat decent

All in all I wouldn't say it's impossible, I would say that it's not a good idea for first-time builders, the majority of whom would most likely be doing this type of install.
Then there's the fact that most of the off-the-shelf torque arm solutions don't really work so well with them

Also, decent 100x9 suspension forks are few and far between nowadays so think if you really want to destroy something that you may have a purpose for down the line and difficulty finding