When it comes to installing a hub motor, you’ve only got two options: a front hub motor or a rear hub motor. (There are actually a few electric bicycles with hub motors mounted as mid-drive motors, but that’s outside the scope of this article.) If you search around, you’ll probably find that the same hub motors are offered in both front and rear hub motor kits, begging the question “what’s the difference?”
Hub motors: weight matters
There are few issues to consider when deciding between a front or rear hub motor. Let’s start with weight.
Generally speaking, you want to try to spread the weight of your electric bicycle out as much as possible, front to back. You don’t want to have all the weight located in one area. Most batteries are mounted in the middle or rear of an ebike, meaning that a front hub motor helps spread the weight forward and can improve weight distribution of your electric bicycle.
Bicycles with heavy rear hub motors and batteries also mounted far to the rear, such as on a rear rack, are prone to “popping wheelies” during acceleration. This is especially true if the motor has fairly high torque and/or the wheels are smaller diameter.
While it may sound fun, this wheelie behavior can become rather annoying when it happens every time you accelerate after a red light or stop sign. It can also be dangerous if it happens when you aren’t expecting it, such as on a slight uphill. Letting someone test ride your ebike and having them flip it over on the first try isn’t good either.
Traction is affected by hub motor placement
Traction is another important consideration. While moving a hub motor forwards to the front wheel solves the problem of weight distribution, it can cause a different problem: traction control. Because there is already very little weight on the front wheel of the ebike, compared to the rear, a front hub motor has less traction.
The higher the voltage and the smaller the wheel, the more likely you are to “peel out” during acceleration with a front hub motor. 36V hub motors on a 26” can still usually get decent traction, but a 20” front hub motor wheel will almost definitely experience a spinning front tire, as will a 48V hub motor on any wheel size.
Most of your body weight is supported by the rear wheel of the bike, which is why a rear hub motor will get much more traction than a front hub motor. It would be very difficult to get a rear hub motor wheel spinning freely on a dry road with nearly any motor running at 48V or less. If you’re one of the guys pushing the limits of high voltage and high power ebikes, you can get about any wheel to spin though.
Hub motors and flat tires
Another thing to think about are flat tires. You are more likely to pick up road debris resulting in a puncture to your rear tire than your front tire.
Why? Because your front tire often kicks up objects laying on the road, such as nails, glass shards, staples, etc that were initially laying flat. They don’t cause much harm to the front tire since their flat surface isn’t sharp. Once they bounce up from the impact of your front tire though, every now and again you’ll be unlucky enough to have it land perfectly aligned to spear your rear tire as it gets passed over for the second time.
Flat tires are much more annoying to fix in a hub motor wheel than a standard wheel, so if you’ve got a rear wheel hub motor, you may find yourself with an annoying flat tire repair down the road. Regardless of whether you go with a front or rear hub motor, my article on avoiding flat tires can help you make this a non-issue.
Consider your hub motor installation
Another advantage of front hub motors is that they are easier to install than rear hub motors. You don’t have to worry about transferring over the freewheel or trying to adjust your derailleur to get rid of that funny chain noise.
With a front hub motor, you simply swap the tire on the wheel and place the motor back into the dropouts. Front hub motor installations are easier than pie, whatever that means.
Rear hub motors still have their advantages
Don’t count out rear hub motors just yet. Many people like their electric bicycle to look like a standard bicycle without any dead giveaways of their “assistance”, so to speak. Many small hub motors nearly disappear behind the gears of a rear wheel, and are often covered by the disc as well. This gives the bike an extra stealthy look and hides the dead giveaway of a naked front hub motor.
Powerful hub motors are also more appropriate for a rear installation because the higher power can be better handled by stronger dropouts in the rear of the bike.
So while front hub motors are easier to install, get fewer flat tires and help spread the weight around, but rear hub motors get better traction, provide smoother acceleration and can appear stealthier.
In practice, many small, weaker hub motors are used in the front of the bike to take advantage of the weight distribution while avoiding issues of tire spin due to the weaker motor, while larger more powerful hub motors are placed in the rear to take advantage of the gains in traction. In the end, it’s all about what works best for you.