Forks for DIY

Joe EE

Active Member
#1
I am considering doing a DIY project on a bike that has “hi-ten steel forks with Chromoly legs”. Does that sound sufficient for installing a hub motor? Thanks in advance.
 

slomoshun

Active Member
#2
Generally, high-tensile and chromoly steels are adequate. The caveats are hub wattage and fork mass. A wispy road fork could be a problem.
 

JRA

Well-Known Member
#4
Plenty, you might want some gears though if you expect to pedal much. SE makes an adult bmx with gears for around $800 that I have my eye on
 

rich c

Administrator
Staff member
#5
Another concern about forks is the axle. A quick release can have a safety recess and open notch. You can still use that, but you need a special washer to make a flush mounting surface.
 

Joe EE

Active Member
#6
Thanks Rich. I don’t think I’m going to go with a quick release though. I think I’m going to bolt that drive wheel on securely. Just agonizing over which bike to use. Today I’m thinking Micargi Falcon GT.
 

Joe EE

Active Member
#8
Thanks for clarifying that. I didn’t think that sounded like a good idea. I have a Surface 604 Colt that has a quick release front wheel and I guess it’s a convenience but I don’t trust it as much as bolts.
 

JRA

Well-Known Member
#9
I meant the current bike forks axle mounting method. You can't quick mount a motor.
My Grin AllAxle front hub motor is set up to easily and securely remove and replace the hub motor without any tools. 1250w peak, aluminum fork never any signs of distress in 2000 not all that easy miles.

My other road bike is basically the same setup and has a bolt on axle that sits in carbon fiber dropouts at the end of a carbon fiber fork. Another 2000 miles of stress free riding from sea level to 11,000'. It takes a wrench and a hex wrench to remove however.

Both forks are inspected regularly as part of the routine maintenance. As one of the few people on here that actually uses a front hub motor I have to give it high marks for primarily road use. Failures can occur with any system due to improper installation and use, or abuse as the case may be.

IMG_5108.JPG
 

Joe EE

Active Member
#10
My Grin AllAxle front hub motor is set up to easily and securely remove and replace the hub motor without any tools. 1250w peak, aluminum fork never any signs of distress in 2000 not all that easy miles.

My other road bike is basically the same setup and has a bolt on axle that sits in carbon fiber dropouts at the end of a carbon fiber fork. Another 2000 miles of stress free riding from sea level to 11,000'. It takes a wrench and a hex wrench to remove however.

Both forks are inspected regularly as part of the routine maintenance. As one of the few people on here that actually uses a front hub motor I have to give it high marks for primarily road use. Failures can occur with any system due to improper installation and use, or abuse as the case may be.

View attachment 19851
My Grin AllAxle front hub motor is set up to easily and securely remove and replace the hub motor without any tools. 1250w peak, aluminum fork never any signs of distress in 2000 not all that easy miles.

My other road bike is basically the same setup and has a bolt on axle that sits in carbon fiber dropouts at the end of a carbon fiber fork. Another 2000 miles of stress free riding from sea level to 11,000'. It takes a wrench and a hex wrench to remove however.

Both forks are inspected regularly as part of the routine maintenance. As one of the few people on here that actually uses a front hub motor I have to give it high marks for primarily road use. Failures can occur with any system due to improper installation and use, or abuse as the case may be.

View attachment 19851
Hey, that’s very interesting info. Why do you think there is so much negativity about installing on anything but steel dropouts? That’s all I have read. I find your experience unique and I think it’s cool you have had success with aluminum and carbon even! Do you it’s because of the specific motor you chose or is there some other reason you can point to.
 

JRA

Well-Known Member
#11
The negativity is from the attempts at people to run their front hubs improperly installed is the short version. The "advice from others" is more a result of reading about it than actually using a front hub that is installed properly.

For a road type bike I like to have my drivetrain completely isolated from the motor. That way I can spin away at whatever amount of pressure and cadence as I desire without the motors influence. The motor maintains a steady output relative to the speed I want to travel. I rode my mid drive mtb on a 22 mile group road ride the other day and I kept up just fine in eco but I found not being able to vary my cadence without speed fluctuations was kind of robotic. For lower speeds where torque is required it is king however.

Weight balance was another factor in that with the front weighted now and the battery in the center triangle as low it will go and my weight on the saddle the bike feels well balanced. One can still do enough of a bunny hop to miss holes and such and handling is very stable even at speeds up to 40+ mph downhill with a tailwind. Corners carve nicely and low speed handling is not affected unless you have the wheel turned and hit on a bunch of power suddenly but that is not an everyday move. The two wheel drive aspect is just icing on the cake.
 
#12
New forum member. Sorry to lurk, but the fork question is a worry of mine. I am thinking of putting a 250 or 350 front hub motor (Leed or Hilltopper) on a Specialized SL3 Roubaix with carbon fork and alum dropouts. For hill assist only, hopefully variable throttle. I have spoken with a guy who put together same on a Dolce which has carbon forks for his wife and it is doing well in assist mode use after 9 months. I am concerned about an on-off button as I like to ride the paceline, too, and power surge is a good way to get kicked from the group. Any mechanical safety concerns?
 

rich c

Administrator
Staff member
#13
What kind of axle on that bike? For quick release you need an adapter washer to be able to use a standard nut because of the safety recess. I guess JRA will tell you it's okay to run in aluminum, but I've understood that to be a bad idea. Isn't the purpose of a carbon fiber fork is weight and flexibility? Not sure flexibility is a good idea with a hub motor.
 
#14
What kind of axle on that bike? For quick release you need an adapter washer to be able to use a standard nut because of the safety recess. I guess JRA will tell you it's okay to run in aluminum, but I've understood that to be a bad idea. Isn't the purpose of a carbon fiber fork is weight and flexibility? Not sure flexibility is a good idea with a hub motor.
Yeah, and getting a metal fork to drop in that year is gonna be hard. It came with a tapered steerer from 1 1/8 - 1 3/8 inch taper. What about a torque arm? And do they have quick release axles for these motors that are 9mm? The front has a standard quick release skewer and the dropouts are 9mm instead of the usually desired 10. Taking out that much material with a file also makes me nervous. I am reluctant to convert my 26" hardtail because everyone knows that can't hang in a paceline... My remaining option is to buy a cheap aluminum road bike that's going to come with a lot lower grade grouppo than I have been riding. Or a vintage steel bike. So many decisions. I am a paunchy 58 yr old who wants to keep up.
 

JRA

Well-Known Member
#15
The only QR Front Hub is the Grin one. It is adaptable to 9mm standard QR, 15 and 20 TA and is the lightest Direct Drive hub on the planet of its watt class. It also includes a built in torque arm that makes a very positive connection and in all my miles on the bike it has held the 9mm QR in place.

You are right about the 1mm axle size difference that all the other nutted axle hubs have which people mainly pull out the file for as you suggest. Taking 1/2mm off each side of the dropout is not that big a deal if it is done correctly. But there were incorrect procedures done that did result in failures that have obviously tainted the front hub system forever it seems. That said my V1 bike has a 9c motor with a nutted axle that I had the dropouts widened on. Oh, and they are carbon fiber. Using the proper washers and locking it all down with a torque arm has worked on that bike for a couple thousand miles also with no ill effect.

And the use of carbon is about weight but not flexibility. It is about its ability to dampen vibrations and have a softer ride quality than aluminum but are as or more stiff torsionally.

I did a group road ride a few weeks ago on my mid drive MTB just to see if I could hang and in the lowest mode and 15psi in the tires I was able to keep up just fine but they were only averaging about 20mph. I missed my hub bike though and the ability to vary my cadence without varying my speed.