So You Want to Hot Rod Your Super 73 – Part 3 – How to Hot Rod Your Bike
The long awaited final post!
A RECAP of PARTS 1 AND 2
A quick recap of Parts 1 and 2: 1) United States federal law defines “electric bikes” as limited to 750 watt motors and not faster than 20 mph with throttle or 28 with pedal assist. Most states follow this scheme and if you go faster, the bike may require a license and cannot be operated on walking and bike paths. European Union countries and the UK are even more mellow: 15.5 mph max assist / 250W power limit.
2). A lot of e-bikes already go faster than what is legal. As a general rule, 750 watts is equivalent to 1 h.p. Super73’s new bikes (S-2 and R Series) feature a 2,000 peak watt motor and appear to be based on their analysis that they can get around the federal 750-watt limit. (The newly released off road RSD style bike is the same motor.)
The R-Series Users Manual says:
Additionally, an “Unlimited” mode enables up to 2000 watts of power under throttle and can reach speeds above 28mph. This mode is exclusively for riding off public roads and on private property.
Similarly, the ONYX bike, from Sweden, has a website front page that advertises a speed of 60 mph and 8hp from a 5,400 watt motor. However, the website states in the FAQ section: "ONYX RCR is limited to a top speed of 20 mph and 750 watt to comply with federal electric bike regulations."
3) If you build or mod a bike to go fast, pay attention to safety. Full face helmet and gloves at a minimum. Armor is prudent. (Yes we sell all that but you can find what you need anywhere - even your local motocross shop).
HOT RODDING - AN OVERVIEW
Some years ago - way back in 2019—Richard Pearce published an article called “Why you Don’t Want a Superfast Electric Bicycle. He described three categories of what he called “Superfast Illegal Bikes.” His article inadvertently provides a nice survey and history of electric bike hot rodding.
1. Chipping / tuning. Pearce observed that on some older models of e-bike all that was required to remove the speed limiter was to turn the speed sensing magnet on the rear wheel spokes sideways to disable it. Another method was to move the magnet in the PAS back so that rotations were sensed to be slower, thus increasing the amount of assist. This was typically done to the Class 1 bikes to bring them up to the speed of Class 3 bikes - 28 mph. Some chipped bikescould exceed 28mph.
In response, E-bike manufacturers began designing the speed limit into the brains of the bike so it was much less easily ‘accessible’ to the end user. In counter-response — in the EU especially — one could find after-market small electronic devices for sale on Ebay to make a bike run illegally fast, known as chipping or tuning. Pearce warned that “usually it means some degree of disassembly of the electronic internals of your e-bike, most likely negating any warranty and potentially causing expensive damage to it.” And that is a good point to bear in mind when you approach a hot rodding job - you are definitely voiding your warranty and assuming that risk.
2. Off-the-shelf models. Pearce’s second category of illegally fast bikes is essentially Super73, ONYX, Juiced, etc. “Some companies advertise themselves as selling complete, ready-to-ride ‘e-bikes’ with superfast speeds (ie more than 28mph), in an attempt to draw attention away from the fact that in no legal sense can they be considered e-bikes. They are implying they have all the legal advantages that e-bikes get i.e. no or very little red tape, without drawing attention to the fact they exceed the speed limit imposed on e-bikes for safety reasons.” Pearce continues in his criticism with this: “Why are the companies that sell such goods often not prosecuted? Many sellers of products that are illegal when used on public roads simply say ‘for use on private land only’. Obviously the vast majority of illegally fast e-bikes will not be used in this way, but it introduces a ‘paper’ defense that puts the legal onus on the riders of such machines.”
3. Retro-fit kits. The last method for hot rodding discussed by Pearce, and the most common one, is to replace the entire motor and controller. This opens up a lot of options. Pearce wrote: “ [I]llegally fast hub motors may be geared to achieve an illegal top speed. They may also put greater stresses on the ‘donor’ bike than it can safely handle.” This is a good thing to keep in mind. If you are going to add a fast motor to a Super73 RX, for example, either buy the new version with the improved front frame or consider having a machine shop weld gussets. Be aware that the companies who make electric bikes deliberately avoided testing them to safety standards of motorized vehicles.
4. Overvolting. Interestingly, the one category that Pearce did not discuss is “overvolting.”This is the original “hot rodding” of electric motors - and the most likely to end in smoked out or burning parts. The speed of a DC motor like the one in your e-bike is entirely voltage dependent. So higher voltages = higher speeds. (This is a speed tip to remember if you ever race your STOCK bike at Apple Valley: be fully and freshly charged!) Hot rodding a motor is simply running more wattage through your motor via a souped up controller. More amps or more voltage (or both) will give you better torque and a higher top speed. In general if you want more speed you run more voltage. And if you want more torque you run more amps, but…in general you get more speed and more torque whenever you pump up the wattage to the motor. Calculating wattage to the motor is simple: voltage X amps = watts to motor.
So if you have a 50-volt battery pack and you run it at 50-amps, you will have a 2500-watt set up, that will get you up to 40-MPH and beyond without pedaling, depending on variables such as tires size and the type of wind in the motor (its “Kv”).
A good resource for hot rodders is the E bikes.ca simulator: ebikes.ca hub motor simulator, which will allow you to estimate speed and efficiency given a particular motor, tire size, voltage, and amperage. Play with this simulator for a while and you will start to understand, and you can then plan a configuration.
Many bikes use a motor that can handle more juice than the stock battery. For example, a 750 watt motor may actually be a 1000 watt motor (the Chinese manufacturers deliberately mislabel the motors so they can be imported for electric bike use and comply with US law). Since motor speed is voltage dependent, using a higher voltage battery is the quickest way to substantially increase your speed. You can get more juice and more speed to a stock 750 watt motor with a bigger battery. However, before you upgrade, you’ll want to check that your controller can handle the increased voltage (most can accept slight over-volting). The voltage rating of your controller is usually written on the capacitors. Do not just swap out your battery without checking – you could risk frying your controller if it can’t handle the higher voltage. Also, note that any battery meter you currently have likely won’t read accurately anymore unless you swap that out for a new meter of appropriate voltage. Many people swear by a product made by Grin Technologies called the Cycle Analyst. There is a lot of technical advice to take in when using this approach that goes beyond the scope of this article. Google “How to Overvolt an Electric Bike” and dig in.
MOTORS AND DROPOUTS
One important piece of information you need when shopping for a fast motor kit for your bike is the “dropout” distance. What is that? Dropout spacing is the measure of the space between the two supports on which your rear axle sits in the rear fork. You can measure this by removing the rear wheel and measuring the distance with a ruler. You need a motor that fits this dropout space. A smaller size can be accommodated by using washers. But a larger size will not fit without spreading the forks out - you don’t want that. Here’s the dropout for Super73 bikes:
Z-1: 150 mm
S-1: 170 mm
S-2/R/RX: 190 mm.
SPEED AND TIRE SIZE
Hub motors turn your tire around, and depending on the diameter of your tire, that will determine the "gearing" and speed of your bike. A big 29-inch tire is going to provide high gearing giving you higher top speed. A small 20-inch tire is going to give you low gearing and better torque and hill climbing. Hub motors, like all electric motors, are more efficient and reliable when they spin fast (high RPMs). The larger your tire, the more likely you are to smoke your motor when you hot-rod it, but you are going to have fun doing it because you will also have higher top speeds.
KITS WE SELL
For our Moon Eyes build, we installed an NB 3000 watt motor and controller kit with a 72 volt battery and 80 amp controller to a new Super73 RX. This combination works together and fits the RX 190 mm dropout. Because this bike was made to show and ride casually, we left the stock battery on top to run our lights and 12 volt stuff. Since we have tested these kits and can vouch for them, we offer them here (fulfilled by MER). The controllers are the well-regarded Sabvoton and will hold up to the 72 volt battery.
For plus or minus every 750 watts you crank through your hub motor you can expect one-horse power. 3000 watts divided by 750 = 4 horses. If you can get 3-HP on a light weight bike frame, then you can hit 30-40 mph easily. With 4-HP, you should see around 50 mph. Definitely do pre-ride checks and tightening of bolts, checking tires and pressure and wear body armor, gloves, and a full face helmet and eye protection.
At 30 - 35 mph the Super 73 bikes have good efficiency, good reliability, good hill climbing ability, at a manageable speed. A 3000 watt motor will easily deliver this plus have that stealthy reserve power for passing. It is definitely worth your while to practice turns and take in some motorcycle training videos before riding fast.
Resources:
For more detailed information about overvaulting and motor kits, check out the blog on electricbike.com here. https://www.electricbike.com/modified-hub-motor/