Hot-rodding an ebike is not as simple as some people might think. That is because you need to consider three critical interlinked components when hot-rodding, and if you don’t change all three components, your ebike probably won’t go any faster, and in fact might go slower or roast something. Think of it as the electric bike bottle neck…if one of your components can’t hold up to the extra power?…you’re not going anywhere faster, and…you might end up in the embarrassing position of pushing your ebike hot rod home (the “walk of shame“):
To begin with, let me say that the three main components of an electric bike are: the motor, controller and battery pack.
If you have bought a commercial ebike and decide you want to go faster, you are not taking on an easy task. It is usually easier and cheaper to just start from scratch, and build an electric bike by converting an old mountain bike you have in the garage that no one is riding. Almost all commercially available ebikes are not very fast to start with, and they pick the cheapest three key components they can to achieve at most a 20-MPH top speed (without pedaling). You can’t just buy some aftermarket part or an upgrade kit that is going to give you an extra horse-power boost, and some extra torque, or extra MPH. The most you may be able to find is a strap-on battery pack that might give you some extra range…but no extra speed or power.
However, a DIY home ebike builder who may very well have started with robust components, might easily be able to modify or swap one component and get more speed.
Lets take a look at the three components individually, and how each one fits into the equation. Think of it like this…the battery is the source of the power, which feeds through the controller into the motor. Of course the battery and motor are the true keys…but they need the controller as a middle-guy to function.
Now lets take apart the three components:
Part 1: The Motor
Starting with the motor, lets start to examine how to get speed out of an ebike. The motor is the end component…
To put it simply the more watts you run to your motor, the more speed and torque you should get. Of course you are lmited by gearing on how fast the bike will go, and each motor has its own gearing or winding. Depending on how a motor is wound it will have high torque or high speed. If your bikes motor winds out at top RPM and your ebike is going only 20-MPH, it won’t go much faster even if you push more amps through it, although for sure you are gonna get more torque (think: wheelie). So when hot rodding a bike you must consider gearing…even if using a hub motor.
Electric bike motors are usually a hub motor but on some more expensive complicated bikes, it may be a mid drive. With mid drives you can change the gearing just by changing a sprocket. The sweetest mid drives allow you to use the bicycles transmission to have multiple gears. However, if you run over 2,000W through the bikes gears, any more will wear out the components very fast (or maybe even break them!)
When you start pumping amps through an electric motor they will also naturally get hot. The larger and heavier the motor the more amps you can pump through it without overheating and ruining your motor. Small electric motors are sexy looking and light weight, but they usually cannot take high heat. (check out the astro motor for the ultimate in small, powerful and sexy ebike motor )
If you are going to pump more amps to an electric motor than it is designed for, you need to consider modifying the motor to dissipate the heat. In general, you can double the amps a motor can handle with active cooling technologies such as blowing air through a motor with a PC cooling fan. More rudimentary methods that work but not quite as good is drilling holes in your motor case (called ventilating). When you find yourself doing things like drilling large holes in your hub motor, or doing a tiny hole so you can inject oil into it so that it dissipates heat better to the side plates…you are on your way to thinking like an ebike hotrodder.
Check out this legendary ebike hotrodder Liveforphysics (LFP), and the penis-shaped holes he drilled into the sideplates of this hubmotor. The end result which was a blue fire ball of plasma flames. This bike cost under $1,500 to build and would do 80-MPH…but was obviously a bit unreliable at those power levels. This video shows you the death of “Pinky”.
So…lets just say…after watching the above video, you feel the need for speed and you decide to hot rod your $3500 Stromer St1 Platinum you just bought, and you bring it into the garage and start drilling holes in your brand new hub motor with your Makita drill. Your ebike is not going to go any faster, because…to pump more power to it, you’re also going to need to change or modify the two other main components…the controller and the battery.
Part 2 : Battery Pack
Now…if the motor is the “buck starts here” part of the equation, the battery is the basis of everything. The battery is where all the power comes from. If your battery is wimpy, then your bike is never going to go fast. The first question you ask yourself when you are trying to determine the hotrodding potential of your battery is…how many volts?. The voltage is a large determinant of how many watts you can crank out of a battery. If you multiply the volts by the amps you got the wattage that your battery is feeding your motor.
A 48-volt battery pack, in general it is going to be much easier to pump 1000 watts to an ebike compared to a 24-volt bike. Of course, if you had a 24-volt battery pack and a 50-amp controller, you could feed 1000 watts to your motor. But a 48-volt controller running at that same 50-amps would provide 2400 watts. For this reason, many home builders start out with battery packs that are 72-volts (and even higher!), but of course, the rest of the system…the controller and motor must be designed to handle this kind of voltage. For most everyday users 48-volts is more than enough voltage…it is enough to easily get an ebike to 40-MPH, which is enough for most mortals on bicycle components.
So once you have a voltage for your ebike pack picked out (hopefully high amperage) the next step is to figure out how much amperage you can crank out of it. Battery packs are limited by several factors on how many amps they can crank out. Most commercial ebikes have a Battery Management System (BMS) that limits the amount of amps they put out. The expensive AllCell pack for example has a 30-amp limit on its 48 volts, meaning you can get a total of 1500 watts out of it.
The highest performance BMS for ebikes currently available for a 48 volt pack will let you get 50-amps out of your 48 volt battery, which again would give you 2400 watts of power. Why do pack makers limit the amount of amperage their packs will put out? Most users want a warranty on their expensive battery packs…when a pack is putting out high amperage for extended amounts of time, it tends to get hot, which greatly reduces its life expectancy.
The other limiting factor of how much amps a battery pack will put out is the quality of its cells. Nice cells such at the Samsung 25R (in the 18650 format) have proven themselves to be stable and effective at putting out high amperage, while still retaining a decent life expectancy. Of course, most pack producers are not going to use expensive high-quality cells…so its important that you ask “which cells make up this pack” when buying a pack.
And finally you need to consider the Watt Hours (WH) of your pack, meaning…what is its capacity? (read our article on calculating watt hours). Basically, the larger the battery pack, the more ability it has to crank out large wattages. Also a fast ebike is by nature not going to be as efficient as a low-powered ebike that is ridden gently.
Part 3: The Controller
It seems that all you need for an ebike is a motor and a battery, but its not that simple. You also need something in the middle called a controller to dose the power to the motor. Most motors these days have hall sensors to make them run smoother, and also require a complex controller to dish out the power. The controller makes sure everything runs smoothly. Your throttle , motor, and battery ALL connect to your controller.
The controllers voltage must match with your battery pack. Also the more amps a controller is able to put out, the more beefy its components are, and the more expensive it becomes. A high-quality controller can actually make your electric motor run quieter, and also make it run smoother and more efficiently (check out our article on sine wave controllers). High amperage controllers, with high quality features are expensive. And if you want small and sexy looking you have to pay even more.
Putting it all Together
So when you plan your electric bike build, or plan on modifying an existing bike, you must consider all three parts of the ebike equation to come up with the correct building blocks for a fast electric bike. When you start to price components, and consider components, you will find that you have to make big compromises because its very difficult to have speed, light weight, reliable, and cheap.
Each Component Can be Sourced Separately for the Ultimate in Affordability
Now lets get into the nitty gritty on how a fast, semi lightweight, reliable electric bike can be built on the cheap. Endless-sphere is a forum made up of the most part of very smart guys trying to build the ultimate affordable fast bike. Lets call them smart cheapskates with a urge to go fast. This is a big generalization, but anyone who knows the endless sphere community knows that it’s true.
How Fast is Reasonable on an Electric Bike?
We at electricbike.com believe 30-MPH is a reasonable number for an electric bike to achieve without pedaling. This is a nice speed that is not too dangerous and allows you to go the speed of traffic. This is currently not available on any commercial available ebike for under $10,000. So basically if you want a reasonable fast electric bike you are going to have to start researching on how to build your own.
Fast Electric Bike = expensive equation
When you consider the three parts to the equation, that’s where it get tricky and expensive to build an ebike. You have three expensive components needed to make an ebike go fast. All three of these components need to be matched together. All of these components need to be either expensive, lightweight, or fast…and its really hard to get all three characteristics. What a few people in the DIY world have figured out is the best chance you have of getting all three is if you hand-select the components yourself and then build the bike yourself. Of course, it is also much cheaper to come up with a fast ebike this way. Most 40-MPH+ ebikes that are currently commercially available cost over $10,000 (such as the Stealth Bomber) , where as many home builders have figured out a way to build a 40-MPH conversion bike for $1,500. Of course these DIY bikes are often times not very pretty, and look like something Frankenstein would ride, and are also very heavy.
And fast ebikes do have their drawbacks:
Read our article on the high cost of electric bike speed.
Hope you enjoyed this article. If you have an example of a fast electric bike you have built using a good combination of components, please post in the comments what it cost and what kind of speeds you get without any pedaling.
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Eric Hicks, Editor… Electribike.com
April, 2015
