durability of carbon fiber fork with front wheel motors

Colleen McGuire

New Member
I have converted a Specialized Allez road bike to e-bike with a bike kit: the battery sits on rear rack and the front wheel hub has the motor. The bike has a carbon fiber fork. I have read a carbon fiber fork is vulnerable to cracking and instantly crashing when the front wheel hub has the motor. Please give me feedback. Is my set-up an accident waiting to happen???
 

Ann M.

Moderator
Colleen, it's not recommended to mount a hub motor on carbon forks. You might want to consider replacing the carbon forks with a rigid steel fork that has good strong dropouts. Also be sure to use some type of torque arm to prevent the wiring harness from ripping if the mounting bolts loosened. Grin makes some the strongest and easy to mount; available for about $30 from ebikes.ca.

Of course, there's another option; sell the hub motor kit and go for a mid drive system if you really need to keep the carbon forks :)
 

Thomas Jaszewski

Well-Known Member
The above advice is best, however, I wouldn't hesitate to mount a SMALL 250W front hub motor with a PAIR of Grin torque arms. But ONLY UNDER THOSE CONDITIONS.

NEW fork would be best, and not that expensive. I could never get along with a single bike. I'd find another frame to build if you are going the kit route.
 

JRA

Well-Known Member
I have about a thousand miles on a carbon fork on my any road bike with a front hub motor. I have been riding it in varied conditions and terrain without any signs of stress. I do use a proper torque arm setup, the one from Grin actually and made sure the interface at the dropouts was correct so that the nuts/washers seat on the flat not the lawyer lips and keep a close eye on it. If it hadn't come with the bike I wouldn't have gone with CF as a first choice and going forward I probably won't spec it again. Aluminum or steel, and still only with a good torque arm setup, for the long run is an overall safer bet.
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Front hub motors, although not popular, have their purpose in the overall scheme of e biking in general. Done right they work as well as anything I have tried, and in some ways better for my needs at least, and installed properly should cause no issues at legal wattage.
 

Thomas Jaszewski

Well-Known Member
Front hub motors, although not popular, have their purpose in the overall scheme of e biking in general. Done right they work as well as anything I have tried, and in some ways better for my needs at least, and installed properly should cause no issues at legal wattage.
Thanks! I have a front drive as well as 5 mid drives and I find myself using that F DD bike more and more. I REALLY like front drives and think it's to bad they get the bum wrap.

I'd do exactly what you have done but what I do and advise are often different. I think it's a decision for a more experienced bike rider hobby mechanic.

Love those Grin arms! I should do a side by side photo of the arms others are selling at nearly the cost. Absolute junk for sale out there. Questionable steel and stamped out parts seem to rule. Even the newest market leader is selling junk.
 

JRA

Well-Known Member
" I think it's a decision for a more experienced bike rider hobby mechanic."

No doubt but if there is a reason to go in this direction the fwd aspect alone makes it worth pursuing for me. It doesn't interfere with my drive train so I can have the range of gearing that I want and can shift at any time necessary. Also if I ever desire to have it be just a regular bike at any time I can swap out the front wheel for the stock one and leave the battery home with only a slight weight penalty for the battery base, controller and wiring. As I am not a racer type that will not make a difference doing a group ride pace.

There are enough issues in setting one up correctly that it does take a more experienced level mechanic to accomplish. The bulk of the Chinese hub motors axle width at 9.5mm which don't fit in 9mm dropouts, disc brake interface and torque arm requirements can take some head scratching. The Any Axle Grin motor I have now still took time to figure out how best to make it work safely but any repeat installations would go fairly quickly and going forward will address any of the problems I have had with the stock Chinese ones.
 

George S.

Well-Known Member
I have two front hubs (Mac, small Golden) and can't see any problems between f/r. I learned from my first install. The Bikes Direct hybrid had an aluminum suspension fork, which is not good. So I bought a Surly fork, overkill, but it looks tough. The other bike I bought because it had a steel fork, though the bike was cheap. Both have the very adaptable Grin torque arm. The Mac is troublesome with disk brakes, the Golden less so. I miss the suspension fork which smoothed out mildly rough terrain.

Aluminum is not supposed to bend before breaking, unlike steel, so steel can be inspected. Steel bikes with good torque arms are reassuring for hub motors, front or rear, but a front fork of steel solves that problem.

I mostly ride a rear hub, the big Golden. That's mostly because of the front suspension, but it also ends up fitting me very well, and has a step through low bar frame. It's easier to change tires on the front hub. The front gives you all wheel drive, in a sense. The front can give a feeling of pulling you through a turn. If there is little weight in front, the starts can be more difficult with the front wheel spinning out.

A front hub with a controller in the wheel makes life simple, especially something thin like the Goldens with few brake issues. Since I had the steel fork and used a rear rack battery (generally more balanced with a front hub), the install was very simple. That's my member photo deep discount cruiser. In many ways it is the most casual and satisfying to ride since I never push it. It works only because it has a motor. Without it it is a torture machine on any grade. You can't stand up or really leverage the pedals in any way. But with a motor it's fine. Motor change things, for me, so I would buy a very basic bike, put a motor on it, and just love it death. Throttles mostly, speed control...
 

Thomas Jaszewski

Well-Known Member
We seem to be sharing some "rule breaking". I did a 750W DD on an aluminum suspension fork for a fellow , a friend, who insisted. He didn't want to give up his 8 spd IGH on an original Townie. This is a year round daily rider for two years. Two Grin torque arms. Dual batteries with gauges and switch to go between. (another idea everyone said no to). I'm sure it has 2-3000 miles. It's just a flat street cruiser so there's no real stress on the fork. Again a matter of how it's used. My new MAC will be a front motor. Until such time I sell off enough for a 2wd. For no good reason other than I'm curious and maybe can.
 

JRA

Well-Known Member
Here are a couple of mid drive/front hub hybrids.

A Bosch/Grin Haibike in Switzerland:
Screen Shot 2017-01-02 at 5.10.16 PM.png


A DIY mid drive/Grin modified Intense in Australia:

Screen Shot 2017-01-02 at 5.07.27 PM.png


Both these are running higher voltage/wattage, the red bike is 3000w, than I am or ever will. The through axle capability of the Grin hub and integral torque arm makes using a front suspension fork possible.

As to two wheel drive I grew up riding Rokons as they were manufactured in my home town and my father had one that he used for hunting and I used to ride all over the place. It was a slow beast and didn't allow for power transfer between the wheels as modern AWD does via a viscous coupling and although it would go anywhere it would get you in trouble at times because there was equal power going to the wheels.

I would think the hard part of getting two electric motors to operate with the same input yet be able to sense which one needs the more power applied as a viscous coupling would do would be tricky. I suppose you could use a lesser wattage motor on either end that might help to simulate it perhaps. Or perhaps control it via PAS by using different modes? I am happy being the viscous coupling between the front and rear drives via my legs/gearing so that is as much as I am going to think about it.
 

Thomas Jaszewski

Well-Known Member
Actually a couple of my former customers have done 2wd and quite successfuly. I have much to learn but the information is there. From what I have gathered it is not tricky at all. That is what I enjoy about endless sphere. Once I had sorted out who to live stent to and to learn from, it became a much more inviting place. It took a long time, but I have time. And a passion. I'm limited due to disability as to frames. i have considered adding front drive to one of my 1000w mid drives but am more interested in doing something and using a motor I have not yet used. Thanks again for the sharing!