If you are looking for help on choosing between a purpose built e-bike, like a Bosch powered Xtracycle, and a converted e-bike, we highly recommend checking out this article first: All you need to know about purpose built e-bikes and converted e-bikes.
IMPORTANT NOTE: When shopping for an e-bike conversion kit, Xtracycle only recommends kits with a max 20 MPH assist. We recommend against kits with an assist higher than 20 MPH or any kit (regardless of max assist level) with throttles.
Let’s get started, shall we?
What types of conversion systems are available?
When it comes to options for electric-bike conversion kits, there are three types to consider:
- Mid-Drive conversion kits: With mid-drive kits, the motor installs on the crank of your frame, where the pedals install on your bike. The battery is installed on the frame or in a bag carried somewhere on the frame.
- Rear hub conversion kits: These kits have a motor in the rear wheel. The battery is installed on the frame or in a bag carried somewhere on the frame.
- Front hub conversion kits: These kits have a motor in the front wheel. The battery is installed on the frame or in a bag carried somewhere on the frame.
Knowing the pros & cons of mid-drive systems vs. hub systems will help you decide what system is best for your needs.
Mid-drive system: pros & cons
- LOTS OF TORQUE: Mid-drive systems have a lot of torque (rotation force) for carrying rear passengers and hauling heavy loads on flat surfaces and up hills. This added torque is thanks to the fact that the mid-drive motor combines the power of your motor and your bike chain to create force.
- IDEAL OPTIONS FOR HILLY AREAS: This added torque prevents mid-drive systems from overheating like hub drive systems, making them ideal for hilly rides where you are carrying lots of weight.
- KEEPS WEIGHT CENTERED ON BIKE: Because the bulk of this system’s weight sits in the middle of a bike (in the crank where the bike pedals are located), a mid-drive converted bike will handle a lot like a regular bike since no significant weight has been added to the front or rear wheel. While the bike might feel heavier, this won’t cause the bike to feel like the front or back moves differently than that of a regular bike.
- CHANGING A TIRE IS THE SAME AS WITH A NON-E-BIKE: Because the electrical components on a mid-drive system are not connected to a front or rear wheel, changing a flat on a bike converted with a mid-drive system is the same as changing the tire on a regular bike. It does not require unplugging wires or carrying any more tools than what you would normally need to change a bike tire.
- MORE MAINTENANCE REQUIRED: The higher torque of a mid-drive system adds a lot of demand on the drivetrain. The drivetrain of a bike is made of the chainrings (the rings of gears attached to the pedals), the front derailleur (the arm that changes your front gears by moving your chain on the front chainring), your chain, the rear cassette (where your rear gear rings are located), and the rear derailleur (the arm that changes your rear gears by moving your chain on the rear cassette). With a hub drive, the power is conveyed directly to the wheel but with a mid-drive system, the power from the motor goes through the entire drivetrain before being passed along to the wheel. Because all the power of your system is spread over these components, they will wear faster or need adjusting more frequently than a regular bike or hub e-bike.
- MORE COMPONENTS INVOLVED WITH THE SYSTEM MEANS MORE PARTS THAT CAN MALFUNCTION: Since the momentum of a mid-drive converted e-bike involves the motor and all the parts of the drivetrain, if any one part of the drivetrain fails, you won’t be able to ride your bike.
- INSTALLATION CAN BE MORE INVOLVED: Installing a mid-drive requires uninstalling a bike’s crank arms, front derailleur, chain, and other drivetrain components. This can lead to the installation being more involved than that of a hub motor, which tends to simply require installing a new wheel and wiring. That said, most mid-drive kits are made to be very user friendly with the assumption that regular riders are installing them.
- CAN BE HIGHER COST: In some cases, mid-drive motors can be higher in cost than hub motors.
Hub drive systems: pros & cons
HUB DRIVE: PROS
- LOWER MAINTENANCE: Hub motor kits are relatively self-contained with few moving parts, which means they require little to no maintenance and adjusting.
- PUTS NO STRAIN ON DRIVETRAIN: The absence of strain on the drivetrain puts less wear and tear on these parts.
- FEWER PARTS TO BREAK: This self-contained system combined with the lack of strain on the drivetrain means the fewer parts at risk of breaking or needing replacing.
- SYSTEM CAN RUN EVEN IF PART OF DRIVETRAIN BREAKS: Since the hub motor is not connected in any way to the bike chain, if your chain breaks, you can still use your motor, ideally to somewhere where you can fix your chain.
- RELATIVELY EASY INSTALLATION: If you can remove your bike’s tire, you can install a hub drive kit. Conversion kits rarely require specialty tools.
- LOWER COST TO PURCHASE: Hub systems tend to be simpler which substantially affects their cost, making their price tag lower.
HUB DRIVE: CONS
- NOT AS MUCH TORQUE AS MID-DRIVE SYSTEM: Hub drive motors rely entirely on the motor to generate torque and they do not use the drivetrain to help generate this force. So they are not as powerful as the mid-drive systems.
- MIGHT NOT BE THE BEST CHOICE FOR HILLY AREAS: Combined with the fact that a hub drive doesn’t utilize a bike’s drivetrain to generate force, the motor on a hub drive systems carries all of the burden of powering a bike up a steep hill with fewer options to downshift within the motor. This can cause hub drive motors to overheat on hills with a 4% grade or higher.
- NOT ALL SYSTEMS HAVE VARIOUS ASSIST MODES: Some hub drive systems only have one or two assist modes. There are systems with various modes.
- HANDLING CAN BE AFFECTED BY WEIGHT ON THE FRONT OR REAR WHEEL: Hub drive systems add the bulk of the weight of the system to the front or rear of the bike. This can cause the bike to handle differently than a regular bike. With rear hub motors this can cause the bike to “fish tail” (when the real wheel slides to the side due to the added weight). For a front hub motor, this can make the front of the bike feel heavy.
- CHANGING A TIRE IS MORE INVOLVED THAN FOR A NON-E-BIKE: Changing out a flat tire on a hub motor can require a few more tools and a little more effort when on the road than for a regular bike or mid-drive e-bike tire.
What system is best for you?
When it comes to deciding on mid-drive vs. hub drive, one of the most important factors to consider is “Do you need the added torque of a mid-drive system to power up hills?” A hub drive system can handle heavy loads on flat or relatively flat surfaces as well as a mid-drive system, but moderate and steep hills might present more of a challenge for a hub drive, especially if they are frequent. If your commute contains multiple steep hills, a hub system might overheat and not be up to the task. In that case, a mid-drive motor might work best for you.
Torque aside, the pros and cons of each system should be considered. What is your budget? Do you want a system that requires more maintenance for the benefit of added torque? One of the easiest ways to navigate all of these questions is to contact the company who manufacturers the system you are interested in buying. This is a great way to get assistance in figure out what system will work best for you, and it is also a fantastic way to figure out if it is a company that stands behind their products. (More on that below in “What systems you should NOT buy.”)
A few quick notes about hub drive systems that might be factors to consider: regen braking and throttles.
Regenerative breaking is a feature available on some hub motors. In short, “regen braking” is when the motor is used to help your bike slow down or brake. The main benefit of regen braking is that it puts less wear on your brake pads. Another benefit, though less substantial, is that the power in the braking is put back into your battery which can slightly increase your range. This slight increase in range, however, is not enough to significantly impact your range capabilities. The main benefit of regen braking is the minimized wear and tear on your brake pads which means you don’t have to replace your pads as often.
Throttles are controls on e-bikes that work like the throttle on a motorcycle. You push a button or twist the handlebar and the bike moves forward, whether you are pedaling or not. Some e-bikes offer this as an option combined with the normal pedal assist (that is when the motor boosts your efforts only when you pedal). Like all choices, there are pros and cons to throttles. Bikes with throttles can move independent of the drivetrain. For example, if your chain breaks, you can use only the throttle to get to the bike shop or home for a repair. With a pedal assist only bike, if your chain breaks, you won’t be able to propel your bike forward. Throttles can also be used to overcome the initial starting lag at stop signs and lights. The downsides of throttles are they can be dangerous for some riders – for example, you are at a stop light and accidentally hit the acceleration button prematurely. They also are a huge drain on the battery and your range so most manufacturers recommend against exclusively using the throttle.
What about choosing the right battery size? We have a fantastic in-depth article about how to choose an e-bike battery here.
What does it take to install the system?
Most e-bike conversion systems are sold as a DIY solution for consumers to electrify their bikes. Because of this, most kits are relatively easy to install. If you can change out your bike’s tire, you can certainly install a hub-drive motor. A mid-drive conversion involves working on the bottom bracket which requires additional tools – like bottom bracket lock ring wrench (which looks like this) and bottom bracket tool (which looks like this). Despite additional tools being required to install a mid-drive system, these are also made to be very user friendly and don’t require any special skills.
Another benefit to doing a DIY installation of your conversion kit is if something goes wrong with your system, you will know your bike and system very well and will likely be knowledgeable enough to trouble shoot any issues that might arise. One of the most common malfunctions for an e-bike is a wire becoming unplugged. If you installed the system yourself, you will know every connection point along your system and will be armed with the skills you need to check them.
If you do not feel comfortable installing your own system, the next best thing is a good friend, bike savvy neighbor or your local bike shop. Keep in mind that most of these folks will be using the same installation manual you have at your disposal, they might just be more skilled with bike maintenance or they might already have all the tools needed.
What systems you should NOT buy.
In short: Do not buy a kit from a company that does not have good customer support. If they don’t respond to calls or emails, if they don’t have good info on their website – etc., don’t buy that kit. With the boom in the demand for e-bikes there comes along those companies wanting to hop on the bandwagon and just make a quick buck. Sure this might make for a lower cost kit but that lower cost comes with a high price, typically in users being stranded without support while building their kit or in trying to repair/service their kit. It can also result in a kit that is dangerous.
As tempting as a low cost kit on an auction site might be, stick with brands that have a good reputation and stellar customer support. Before buying a kit, send the manufacturer an email, call them up, ask them questions. Their eagerness to respond and ability to help answer questions will be a great indicator of whether you should trust them with your investment.
Reading reviews on-line in various forums – social media, blogs, etc. – is another great way to get to know the system you want to invest in.