Building An Electric Downhill Bike: A Step-By-Step Guide

Electric downhill bikes are an emerging trend in the world of mountain biking, offering riders a unique blend of thrill and assistance. While some purists argue that the inclusion of motors takes away from the traditional mountain biking experience, others embrace the advantages it brings, such as making uphill rides less tiring. Building your own electric downhill bike can be a fun and rewarding project, but it's important to prioritize safety and ensure compliance with local laws. In this article, we will delve into the process of constructing an electric downhill bike, covering essential components, safety considerations, and the legal implications of this emerging technology.

Choosing a donor bike

Bike Type and Purpose

Firstly, consider the type of riding you plan to do. If you intend to ride downhill and on challenging terrain, look for a full-suspension electric mountain bike (eMTB). These models typically offer 150-180mm of travel and more extreme geometry, ensuring stability and shock absorption for high-speed, downhill riding. On the other hand, if you plan to ride on gravel roads and casual off-road trails, a hardtail eMTB or electric hybrid with front suspension might be more suitable, offering a comfortable, upright riding position for extended periods.

Gearing and Motor Placement

The gearing system of your donor bike will impact its performance on downhill trails. While mid-drive motors are great for climbing hills, they are less efficient for downhill riding. Instead, consider a rear hub motor, which can provide more than enough power for downhill riding without the need for complicated gearing systems. If you opt for a front hub motor, ensure your donor bike has steel rigid forks to handle the additional weight and torque.

Braking System

Quality brakes are crucial for downhill riding, as they provide the necessary stopping power for heavier bikes travelling at high speeds. Look for hydraulic disc brakes with large disc rotors (180mm or more) and heavy-duty calipers to ensure safe and effective braking during your downhill adventures.

Frame and Wheel Size

The frame and wheel size of your donor bike will impact its handling and performance. Carbon fibre frames are lightweight but expensive, while aluminium frames are more affordable yet heavier. For downhill riding, consider a longer, lower, and slacker frame geometry, which is designed for gravity-focused riding. Additionally, larger wheels (29" or 27.5") offer improved speed and rollover power, making them a good choice for downhill riding.

Budget and Condition

Finally, consider your budget and the condition of the donor bike. You can find good deals on second-hand bikes, but be mindful of potential restoration costs if the bike is not in good condition. Ensure that essential components like turn signals, headlights, and horns are functional. It is also worth checking the chain, cassette, and brakes for wear and tear, as these may need to be replaced.

Remember, the key is to find a donor bike that suits your specific needs for downhill riding, and with the right modifications, you'll be flying down those trails in no time!

Buying a conversion kit

Electric bike conversion kits are a great way to add a boost to your current bike setup without the price tag of a full e-bike. When buying a conversion kit, there are several factors to consider. Firstly, you need to ensure the kit will fit the dimensions of your bike, including the fork width, rear stay width, wheel sizes, and brake type. You also need to decide on the location of the motor, with front hub motors being the easiest to fit, and mid-drive motors requiring more effort.

When it comes to power, bigger batteries are better if you're looking for a commuting tool. A 52-volt, 13.5-amp battery, for example, will provide ample power. It's also important to consider the charger, as incompatibility is a common cause of fires in electric bikes. To estimate the range of your setup, you can use the basic formula that a 100Wh (Watt-Hour) battery will last for one hour at 100 watts of power output.

There are several conversion kits available on the market, including the Swytch Kit, which offers a universal fit for all popular wheel sizes and comes with everything you need, including a battery, charger, pedal sensor, and motor wheel. The Bafang kit is another option, offering a front hub-based motor with various amp-hour choices for the power pack. If you're looking for a more powerful setup, you can find 1,000 W direct-drive kits and 48V Li-ion batteries that can help you achieve speeds of up to 30 mph.

While conversion kits can be a great option, it's important to note that they may void your bike's warranty, as bicycle brands typically do not condone converting their products into electric bicycles. Additionally, electric downhill bikes may not be for everyone, as some consider them cheating and argue that they take away from the traditional mountain biking experience.

Choosing a battery

When choosing a battery, it is important to consider the size and range. Generally, a larger battery with a longer range will provide better performance, but it will also add weight and cost to the bike. As the weight of the bike increases, it will require more effort from the rider to handle and manoeuvre. Therefore, it is essential to strike a balance between range and weight, depending on your specific needs and riding style.

The type of battery you choose will also impact the performance of your electric downhill bike. Lithium-ion batteries, for example, are known to be temperamental and require careful charging to prolong their life. It is advisable to only charge these batteries up to 80% or 90% to ensure they last longer. Additionally, consider the voltage and amperage of the battery. A 48V Li-ion battery is commonly used for electric bicycles with speeds up to 30 mph, while a 52-volt, 13.5-amp battery can provide higher speeds of up to 40 mph.

It is also worth noting that the battery technology you choose may impact your riding experience. Some batteries can be charged through regenerative braking, which can be beneficial in hilly areas. However, this technology tends to be expensive and may create drag while riding, impacting the overall performance of the bike.

Lastly, it is important to consider the safety implications of the battery you choose. Fast electric bicycles can be dangerous, and it is recommended to start with a reasonably powered electric bicycle first to gain experience. Additionally, check your local laws to ensure that your electric downhill bike complies with any regulations or requirements, such as adding mirrors and lights for on-road use.

Installing the battery

When installing the battery for your electric downhill bike, there are a few things to consider. Firstly, you'll want to ensure that the battery is securely attached to the bike. Some batteries come with a mount that can be attached to the water bottle cage mounting studs or the frame of the bike. If your battery doesn't have a mount, you can purchase an adapter to attach it to the water bottle mounts, or use extra attachment straps to secure it to the underside of the bottom tube. It is imperative to ensure that the battery does not move around, as this can cause damage.

Another consideration is the size and weight of the battery. If you're looking for a lightweight option that won't slow you down on those downhill adventures, consider a smaller battery or a battery that can be stored in a backpack. LIFT-MTB, for example, offers lightweight batteries that can be easily carried in a backpack, providing better performance and a more enjoyable riding experience.

When choosing a battery, it's also important to think about the voltage and ampere-hour rating. For a powerful electric downhill bike, you may want to opt for a battery with a higher voltage, such as 48V or even 52V. Additionally, consider the quality of the battery cells, as this will impact the performance and longevity of your battery.

Lastly, don't forget about safety. Lithium-ion batteries, for instance, are known to be temperamental, so it's important to invest in a good charger that will prolong their life. Additionally, some batteries come in fireproof protective bags for added safety.

Safety considerations

Electric downhill bikes can be a lot of fun, but safety should be a priority. Here are some essential safety considerations to keep in mind when building and riding your electric downhill bike:

Firstly, it is important to recognize that building and riding an electric downhill bike is not without risk. Electric downhill bikes are powerful machines, and any modifications or improper assembly can lead to unsafe conditions. It is recommended to have experience building custom electric bicycles before attempting to build your own high-speed electric downhill bike. Start with a lower-powered electric bicycle to gain familiarity with the process and the technology.

Next, it is crucial to select a suitable donor bike for your conversion project. Choose a high-quality mountain bike designed to handle speeds over 40 mph, as these bikes have rugged frames that can withstand high-speed downhill conditions. Ensure that the donor bike's brakes are upgraded and capable of sustaining high speeds. Hydraulic disc brake systems with 4 pistons are recommended for maximum stopping power. Check your brake pads regularly and service the brake system when the lever starts to feel 'spongy'. Remember to prioritize braking on the rear wheel when slowing down or stopping, especially when riding downhill.

Additionally, pay close attention to local laws and regulations regarding electric bicycles. These regulations vary depending on your location, so educate yourself on the rules and restrictions that apply to your area. Some areas may require you to add mirrors and lights or register your bike as a moped or light motorcycle. Check with your local authorities or legislation to ensure you are compliant and can ride safely and legally.

Furthermore, be mindful of battery safety. Lithium-ion batteries used in electric bicycles are sensitive and require careful handling. Avoid charging them up to 100% to prolong their lifespan. Consider investing in a charger that can limit the charge to 80% or 90%. Also, familiarize yourself with battery best practices, safety certifications, and proper disposal procedures for damaged batteries.

Lastly, always wear appropriate safety gear when riding your electric downhill bike. This includes a helmet and other protective equipment to minimize the risk of serious injury in the event of an accident. Stay vigilant and follow road safety rules, especially when riding in hazardous weather conditions or on challenging terrain.

Frequently asked questions