Friction Drives; Ultra-light and Surprisingly Powerful

A Friction-Drive (FD) is an electric bike drive system that spins a roller that’s pressed against the bicycles tire. FDs have been around for over 100 years. Small gasoline engines (the size of a chainsaw) have been used to drive a roller on a bicycle tire almost as soon as small gasoline engines were invented. A company that still makes these kits is

An electric friction drive patent by John Schnepf from 1899


A concern that some builders have about an FD is that…in wet weather, the roller might slip some. This is somewhat true in my experience, however…there are some unique advantages to an electric-FD that may make them worth consideration over a common hub-motor. Several creative FD builds have been mounted to the seat-post, and if you’re using a lever-actuated post-clamp, you can easily and quickly remove both the seat and drive from the bike with no tools. This can be useful to a college student who must park his bike outside, or an apartment-dweller who lives on the upper floor and wishes to leave the bike at ground level.


FDs that mount to the seat-post, and drive the top of the rear tire


There is a limit to how much power we can be put through a friction drive, because acceleration is dependent on the roller keeping a solid contact with a small patch of the tire. Increasing the peak power of your drive by a little too much may result in the roller simply spinning-out. I have personally put 1000W through my system while maintaining constant roller traction, and several builds have been configured for a top-speed of 30-MPH. Both of these goals can be met with a drive that is surprisingly small and light, if you are willing to use some components that have been designed for RC model planes. (see our Astro motor story)

A builder named Kepler noticed that the style of motor frequently used for RC models is called an “outrunner”, and it spins its outer-shell. As a result, a drive could be made where the motor is the roller, rather than attaching a separate roller to the motor-shaft. He is from Australia, and he has begun marketing these drives to the public which he calls the Eboost Power Assist. (visit him here)

One clear feature of this shell-drive design is that the starting-torque of the motor is what causes it to swing out and grab the tire. Once they are touching, the spinning shell pulls itself deeper into the tread as needed. This also means that when the motor is unpowered, it does not touch the tire at all, and because of this, there is absolutely no drag when simply pedaling, so it freewheels exactly like a regular bike. This system is the smallest and lightest E-drive I can imagine for a bike, and is very quick and easy to install. This system installs and uninstalls so easily that you can decide to go with or without your drive system when you take your bike out. It takes less than 2 minutes to install the system once you are use to it. The Eboost can be used on 90% of bikes, but not bikes with rear suspension.


A typical Kepler “eboost” drive, with an 8300-mAh LiPo battery


When using a shell-drive, the large diameter roller (2-1/2 inches for a 63mm diameter RC motor) will draw fairly high peak amps when powering-up from a dead stop. The constant-draw amps are very low due to the high reduction and high RPMs of these small but powerful RC motors. For a Kepler-style RC motor-shell drive, I recommend using an RC-controller that is rated for a minimum continuous output of 100-amps. If you want a physically small battery, you may need to use a high C-rate LiPo battery. (recent edit: if you need high-current batteries, they are now available in the very safe 18650 format from the cordless tool industry “Amazing new cells 18650 cells for ebike batteries in 2015“)

I have used some of the affordable generic Electronic-Speed-Controllers (ESCs) for RC-motors. Some of them suffered from a “loss of sync” failure. The ESC I recommend is from Castle Creations, and I have never had any problems with them. I would use the Phoenix ICE-100 (made for 18V-34V, 100-Amps). Also, in order to reduce “voltage ripple” (which could damage the ESC), you should add two low-ESR capacitors to the red/black power inputs to the ESC. Like this $2 example.

Why would someone want an FD instead of a hub-motor? They are not for everybody…

If you want to go faster than 30-MPH…I would only recommend a DD-hub and a voltage that is more than 48V. Be aware that even if you have a short commute, you may still need at least a 15-Ah size of battery to have an adequate C-rate when using the popular LiFePO4 battery chemistry.

If you have medium-difficulty hills, and spend most of your time at less than 27-MPH, most people seem to be very happy with 36V / 48V and a geared hub. Since the internal gears allow the motor to spin five times faster than the wheel, peak amps on start-up are lower than a DD-hub, and a modest 10-aH battery should be adequate as the minimum.

But…If you live where it’s pretty dry, you like the idea of an ultra-light drive, and you think you can be happy with a 1000W system that tops out at around 27-MPH, a Friction-Drive might be an option for you. And in spite of how small an RC-motor appears, the hill-climbing power is very good…

Parts list for a total of roughly $800
$350 (Aus) Eboost  drive system, seatpost mount with space for one LiPo battery pack

$60, 170-kV Aeolian RC motor / 22V, 25-MPH

$140 Phoenix ICE-100 controller

$45 LiPo battery 22V / 5-Ah

$80 power supply and charger for 6S LiPo

 = $800 plus taxes and shipping


For more information about the Kepler Drive system, read the endless-sphere post here.

Coming soon, information on the similar “Commuter Booster” friction drive from Adrian (currently in beta testing). Also, my personal prototype RC-drive where the roller and motor are separate (designed by EVTodd), and an argument for the possible benefits.

10 reason why you might choose a friction drive system over a hub motor:

  1. Friction drives look different, and appeal to the ebike geek in a lot of us because they were used historically on some of the first ebikes.
  2. Friction drives are the easiest install imaginable, so much so that your bike will be able to double as a regular bike since the drive system can be taken off of it in a minutes time.
  3. Friction drives offer much more power to weight than a hub motor.
  4. Friction drives mean no extra weight in the wheels, a basis for good ride feel.
  5. Friction drives mean weight is centralized, in the middle of the bike, making a well balanced ebike.
  6. Friciton drives are an ideal solution for a road bike or a fixie bike where there is not much space in the hub for a hub motor.
  7. Friction drives allow you to use a super cool rc motor to drive your bike.
  8. Friction drives are rare. Hub motors are everywhere, the basis for 95% of modern ebikes.
  9. Some people like the motor noise a friction drive makes….more of a sensation of riding an electric bike.
  10. Depending how configured, a friction drive can be more efficient than a hub motor.
10 reasons to stick with a hub motor and forget about a friction drive
  1. Hub motors are made in mass quantities and are therefore more cost efficient. More motor for the money.
  2. Hub motors are readily avialable.
  3. Hub motors are so cheap that if you blow one out you just replace it no sleep lost.
  4. Hub motors are comparably silent.
  5. Most hub motors can be ridden in the rain or wet conditons.
  6. Most Hub motors are super reliable and proven so.
  7. Hub motors make you feel like part of a huge crowd of like wised thinkers.
  8. Some hub motors can be over-volted to give you incredible performance, both top speed and hill climbing.
  9. Hub motors can be used on rear suspension bike, a friction drive cannot.
  10. Hub motors properly installed are much more stealthy than a friction drive unit


My personal DIY Friction Drive. The neck of the drive is an adjustable angle handlebar stem.


A drive I made for ES-member “rearengine”, mounted to the V-brake flange of a recumbent, using the same roller and motor as my personal DIY kit.


Adrians "Commuter Booster"
Adrians “Commuter Booster”

converted goped friction drive!


Keplers first prototype for his “Eboost” drive



A commercially available friction drive, with two motors that drive both sides of the rear tire.


Zap Bike, one of the first modern commercially available ebikes was a friction drive. Two small brushed motors share the same shaft that holds a roller against the rear tire.


Additions to this Article in 2015

This was the first article I ever wrote for I noticed recently that it is still getting a significant amount of clicks, so…I want to update a few things:

A company called Rubbee has burst on the scene with a clever friction drive design.



In December of 2015, a company called ShareRoller launched a successful Indiegogo campaign to fund their expansion. It is a well designed unit that is definitely worth consideration.


The ShareRoller friction drive.


Written by Ron/Spinningmagnets, May 2012

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego. Hydraulic mechanic in the 1980's/Los Angeles. Heavy equipment operator in the 1990's/traveled to various locations. Dump truck driver in the 2000's/SW Utah. Currently a water plant operator since 2010/NW Kansas


  1. I think the old Zap Bikes were friction drive too.

    • You are right they were…i will find a picture and post in story.

  2. Do you guys sell just an engine? If so, how much would one go for?

  3. Shouldn’t Rubbee be listed here? Seems like they are one of the best in the friction field now.. 🙂

    • Well…sleekest and most polished perhaps.Have you actually tried one yet? I will be doubling the battery capacity as well as addressing the motor noise soon. And mine is nearly new! Practically a piece of art yet under-powered and I wish I was brave enough to increase the voltage to the motor. I would estimate the polyurethane roller absorbs 20 or more percent of the output. Try pedaling with the roller engaged and the electric off. Whew! Still fun tho…terrific design. Very portable. I like mine but hope some tweaking will bring it alive!

  4. All good ideas. Thinking of working on something similar to one of the above but solar powered so I have all the range I need for day time commuting. For night time trips I’ll need to figure out a way to make it so it can go from solar to battery power.

  5. I’d like to try one of these variations on my mountain bike/xtracycle cargo bike. I’d like to tour on it. So, battery life and climbing power would be a plus. But I do like to go fast. .. .. ; ) ,, Any ideas??

  6. go-e have a friction drive called ONwheel. Only 930g and up to 600W and 45km/h. I think this will be one of the most powerfull and light weight system.

  7. The Commuter Booster seems to be dead. The web page looks nice but no updates in several years.

  8. I have the 1000 watt 48v Lanke Leisi C-750 Plus from SUPER SWEET!!!! This is almost as fun as jet skiing and because it is almost free to charge it is the best imo

  9. FD,s can be used on rear suspension bikes,I’m running DeWalt 54v brushless chainsaw motor on diamondback mason 27.5,I use the motor on lever operated hinge,60kmh 1500w

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