Electric Bike Motor Kit for Thru-Axle?

Court

Administrator
Staff member
#1
Hi guys, I received the following question via email and wanted to share my response here and ask for input from the community so that more people could benefit.

Eric asked "I am wondering if you would be aware of any conversion kit (front or back wheel) that supports both a thru axle quick release and disk brakes?"
 

Court

Administrator
Staff member
#2
I personally have not seen ebike kits that work with thru-axles because the motor has to push against a fixed axle in order to turn the wheel (front or back wheel). Most hub motors are connected to a 12 mm threaded axle with 9 mm flats that slide into a dropout. Some of the more powerful geared or gearless motors and kits come with torque arms that attach to the axle outside of the dropout and help to spread the forces up into the fork (if it's a front kit), or chain stay and seat stay (if it's a rear kit). I've attached a couple of images below that helps to show this.

This picture shows the inside of a geared hub motor which is fixed to the axle along with the power cable running through and exiting at the end. You can see the threaded portion of the 12 mm axle as well as the flat cuts that allow it to slide into a fork dropout and push against the dropouts.

electric-bike-outfitters-phantom-kit-inside-of-geared-ebike-motor.jpg

This picture shows a heavy-duty gearless hub motor mounted to a cheap suspension fork, in order to fortify the dropouts and keep the motor axle from "chewing" into them as the motor starts and stops (and drags due to cogging in this case), a large torque arm has been installed. It has been connected with a metal worm drive fastener often used for securing ducts and hoses.

electric-bike-outfitters-clydesdale-2-0-kit-heavy-duty-torque-arm.jpg

In summary, while many hub motor style ebike kits do support disc brakes (where the disc can mount directly to the outer casing of the motor), I have not seen any kits that are compatible with thru-axle configurations. Axles are built-in to the motor and provide something for the motor to push against, with a thru-axle, the hub motor wouldn't have anything to push against to generate force and move the wheel and the power cable that connects the motor to the controller and battery would spin and get shredded off. Most designs that I have seen (with external batteries) have the power cable run through the axle and exit the right or left side.
 

Ravi Kempaiah

Well-Known Member
#3
I personally have not seen ebike kits that work with thru-axles because the motor has to push against a fixed axle in order to turn the wheel (front or back wheel). Most hub motors are connected to a 12 mm threaded axle with 9 mm flats that slide into a dropout. Some of the more powerful geared or gearless motors and kits come with torque arms that attach to the axle outside of the dropout and help to spread the forces up into the fork (if it's a front kit), or chain stay and seat stay (if it's a rear kit). I've attached a couple of images below that helps to show this.

In summary, while many hub motor style ebike kits do support disc brakes (where the disc can mount directly to the outer casing of the motor), I have not seen any kits that are compatible with thru-axle configurations. Axles are built-in to the motor and provide something for the motor to push against, with a thru-axle, the hub motor wouldn't have anything to push against to generate force and move the wheel and the power cable that connects the motor to the controller and battery would spin and get shredded off. Most designs that I have seen (with external batteries) have the power cable run through the axle and exit the right or left side.
There are few options:

Grin has thru axle options:
http://www.ebikes.ca/shop/electric-bicycle-parts/motors/grinhub-std.html
@JRA has run motors of this kind on his bikes. His may be QR but I have seen thru axle builds elsewhere.

thru-axle-adapters.jpg

The second options is from Bafang.
They just released a thru-axle motor made for fast commuter and MTB builds.
More details can be found here.

bafang-thru-axle-ebike-hub-motor.png
 
Last edited by a moderator:

JRA

Well-Known Member
#5
Note that the All-Axle Grin motor is front only. I do use a QR only as I haven't found a thru axle fork yet that suits my needs. And to boot road forks, mine is on a road bike, are 12mm a fact I have made Grin aware of. But the integrated torque arm not shown in the above pic is what really makes this motor stand out as all others must use one that fits the axle flats and attach to the fork/frame. Regardless it is always a good idea front or rear to use a solid torque arm.

Screen Shot 2018-05-20 at 8.30.05 PM.png




The mount that I made to secure it allows me to take off the hub motor without any tools. All I have to do is undo three connectors on the right side (which exit the motor independently from the axle at all as seen above, which are hiding the torque arm in this picture. The brass strap is the mount. It has a pin that fits into the TA slot so that it just slides in and out. Even running 1200w peak I have never observed any sort of axle movement nor undo stress the aluminum fork.

unnamed.png


Also the Grin motor is one of the few hub motors that is 32h. This really opens the up the choices for rims, especially TLR ones to easily allow tubeless to be used.

This motor has been as powerful as I need it to be, very reliable, efficient, has regen and super quiet, as in silent. Oh, and a little under 4kg which is around what a geared hub motor weighs and a couple kg's less than other hub motors of its class. Bike as shown weighed a little under 20kg. Due to the loss of the extra weight which acts like a heat sink the addition of Grin's Statorade keeps it cool enough to allow for sporty climbing if that is your thing and is easy to keep in the proper temp range.

Also all the Asian hub motors I have installed have 10mm flats which is a bit of a mystery to me? Although that standard has existed in the past the QR standard has been 9mm for years now here and abroad so in order to get one to fit some filing must be done and by far the fastest, easiest and most precise way to do this by hand is with a 10mm rotary burr file in a die grinder. They make them for aluminum as well as steel.
 

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