Posted 01.25.2016 in Articles
Early in the development of electric bikes, the rear-wheel hub motor was the undisputed champ. Hub motors were the most effective, easily implemented, and least-expensive route to take when a rider or e-bike manufacturer installed an electric drive system.
Over the last few years, mid-drive motors have become a viable alternative to hub drives, but the majority of electric bicycles still use hub drives. Part of the beauty of hub drive systems is that they are completely separate from the rest of the bike’s drivetrain. Because hub motors are easily integrated into bicycle designs, you can find these drive systems on all kinds of bikes: urban commuters, cargo bikes, tricycles, pedicabs, recumbents. Bike manufacturers use hub motors to build electric bicycles using existing frames and build electric- specific frames to make the battery, motor controller and rider interface better integrated. They can be easily added to traditional bikes via aftermarket kits by DIY modders. There are even all-in-one wheel kits that include motor, controller and sometimes even a small battery in the hub.
Early model motors used internal “brush” contacts that wear out and require replacement. Today, almost all manufacturers have moved to a maintenance-free brushless design.
Hub motors are either gearless direct drive or geared. Geared motors, just as the name states, use gears which allow the motor to be lighter and smaller and still exert maximum output. The downside is the gears produce friction that creates addition noise and wear. So, in theory, because there are more moving parts inside, these hubs can wear out faster then their gearless counterparts. A benefit of geared drives is the ability for these hubs to freewheel. When electricity isn’t applied, the gears disengage and there is no drag, so the bike rolls with less resistance.
Direct drive gearless motors are simpler and have fewer moving parts. There are very few maintenance issues, and gearless motors are incredibly quiet. Some direct drive systems are configured to provide regenerative capabilities. When coasting or braking, a regenerative system turns the motor into a generator that creates electricity that can be used to charge the battery. Regen systems require more complex controllers to protect against overcharging, which can add to the cost of the system. A possible drawback to direct drive systems is they do not completely freewheel. If there is no power supplied to the system there will be a small amount of drag.
Hub motors take the place of the traditional hub. The axle goes through the hub motor and attaches it to either the rear triangle dropouts or the fork dropouts depending on the hub motor type. As the hub generates force to propel the bicycle forward, some of the energy produced is transferred to the frame. Electric bike manufacturers calculate the amount of force to be exerted on the frame or fork and beef up the dropouts to accommodate for the added stress. If installing a kit onto a traditional bike, talk to the kit manufacturer or dealer to ensure your bike’s dropouts can handle the torque.
Because hub motors are separate from the bike’s drive gears, chain or belt, sprockets, cranks and derailleur system, shifting gears is handled exactly the same as if the hub motor wasn’t there. The hub motor just gives you that extra oomph to climb hills with less effort, get to work without getting sweaty, or give you extra range when out riding for exercise or recreation.
Hub motors add weight toward whichever end of the bike the are mounted. For most commuters this isn’t a big issue, but it can play a role in bike handling if the bike is used for off-road riding.
Rear hub motors provide good traction because more of the rider’s weight is positioned over the drive wheel. Even though there are a large variety of power output ranges, most frames can handle the extra torque as long as the rear dropouts are well made or reinforced.
Wheels with rear hub motors can be cumbersome to remove/ install. With the added weight of at the rear of the bike, positioning of the battery is important so the bike doesn’t become rear heavy.
Front hub motors are easy to remove and install making maintenance and repair easier. Since the rear wheel is kept unchanged, makers can use any combination of wheel, gears, cranks, chain ring, derailleur, chain or belt wanted.
Weight is more evenly distributed because additional weight is out front.
Front wheel drives create an all-wheel drive system that adds traction in some terrains. Front wheel drive hubs may lose traction when on wet roads. Front hub systems require a sturdy fork with beefy dropouts. This can be easily remedied with aftermarket forks. It is recommended you talk to the hub manufacturer or retailer to ensure the fork on your bike is compatible with the hub.
This article originally appeared in the Electric Bike Buyer’s Guide included in the Q3 2015 issue of Electric Car Insider magazine. The Buyer’s Guide features 30 electric bicycle profiles. Each full-page profile includes multiple photos and important specifications so buyers can make informed buying decisions. The most current print issue of the magazine is available on hundreds of independent newsstands in the U.S and Canada including Barnes & Noble, Hastings and Chapters Indigo. Never miss an issue by subscribing today.