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Motorizing a flip-flop fixie racing bike

Hi, I am looking into modifying my flip-flop fixie racing bike by mounting a 750w motor beneath the seat and running a standard bike chain between the motor and the fixed gear. MY1020 should work just fine for this application. I just have a few questions about the product. -Can I order this motor with a standard bicycle chain drive gear? -Do you also sell the battery specified for this motor? If not, where can I buy one? -And lastly, if your motor turns out to be suitable for my application and I need dozens of them at a time, can your company offer a quantity discount? Thank you very much for your time and consideration, -Jesse.

I searched online and found that most fixie racing bikes have around 24" wheels. If your bike has that large of a wheel then a gear motor would be needed if you want to keep the wheel sprocket size small (14-22 teeth). If an MY1020 motor was used with a 24" wheel then an 80 tooth or larger wheel sprocket would be needed, and an 80 tooth sprocket has a 12.75" diameter which is almost the size of a medium pizza. Either way will work though, it just depends what size wheel sprocket you want to use. 

We carry an 11 tooth bicycle chain sprocket that fits MY1020 motors. It is our item # SPR-B10100 which is available on our Bicycle Sprockets Page. On the same page, we also carry a bicycle chain sprocket item # SPR-B1711 for most of our MY1020Z Gear Motors that are available in both 450 Watt and 600 Watt versions. 

We carry batteries, controllers, throttles, power switches, etc that work with our motors so we can supply all of the electrical items that are needed. We can make a list of compatible parts or we can make a pre-wired kit with matching and labeled connectors out of the parts.

We can help with choosing the right sprocket size to obtain the top speed that you want the bicycle to travel at under the power of the motor. We do offer discounts on bulk quantity purchases. 

Please let us know if you have any questions and we can take it from there?

This bike has 700 X 25c tires, which are 27 inch. When you mention 80 tooth gears, I presume you're thinking of start up gear ratios. With this bike, I plan to start by pedaling (it has a single gear pedal that drives a freewheel sprocket on the right side) then once I'm going about 15-20 mph (that's about as fast as it goes pedaling... It's really just geared for quick start ups) I can engage the motor and stop pedaling. My aim is to get a good top speed of at least 40 mph, if possible, with only one gear. The bike has a 17 tooth fixed sprocket on the left side of the back wheel. Would it be possible to find the size of gear that wouldn't put too much strain on the motor engaging it at 15-20 mph but could eventually accelerate the bike to around 40, or possibly faster? I was thinking probably a smaller gear, like the 11 tooth you suggested.

The 80 tooth wheel sprocket with 24" wheel calculation was relating to a top speed of 25 MPH that a 750 Watt 2750 RPM motor could obtain without the addition of human power. This calculation was a little padded as a 750 Watt motor could obtain 31 MPH on flat ground with no headwind. 

For a 40 MPH top speed on flat ground with no headwind, 1500 Watts of electric motor power, or 1500 Watts of electric motor+human power would be needed.  

On flat ground with no headwind, virtually all of the power needed to sustain a certain speed goes towards overcoming aerodynamic drag (air resistance). Theoretically, a person who can output 500 Watts of pedal power could propel a bicycle to incredible speeds such as 100 MPH in a perfect vacuum. However, in earth's atmosphere, the air resistance would only allow for a 27 MPH top speed of the same person. The amount of power that aerodynamic drag consumes follows a non-linear curve with respect to speed, so the faster the vehicle travels at the more power per MPH is needed to propel the vehicle. For example, 500 Watts of power can propel a bicycle to 27 MPH, 1000 Watts can propel to 35 MPH, 1500 Watts can propel to 40 MPH, and 3000 Watts can propel to 50 MPH.

A 1600 Watt motor could propel a bike to 40 MPH on flat ground with no headwind. Here is an example of a gear ratio for a 40 MPH top speed using our 48 Volt 1600 Watt 4800 RPM brushless motor along with a 27" wheel.

Please let us know if you have any questions. 

I see. So basically, I can use any gearing ratio I want with a 750w motor, but I will never exceed 31 mph on flat ground with no wind factor. And toying with different gear ratios will only take away from your top speed to add torque, or vice versa, to the point you either have all torque and no speed or you're geared too high so that you don't have the torque necessary to reach your motor's target RPMs. Makes sense. I'm still going to have to go with a 750w motor to remain 'bike lane legal' in my state. Although, I was hoping, since my bike weighs about 20 pounds, has 27 inch wheels and is exceptionally aerodynamic, it would possibly be able to push 35-40 mph on 750 watts :-/ Well, I'm still probably going to push ahead with the project, and I was just wondering how long one of your 36v battery packs will run a 750w motor continuously at full throttle on a single charge. Thanks again for all your help.
I see you have several types of batteries, but none exceeding 24v that I saw. Would I need to combine several 12v batteries to produce 36v or should I look into purchasing other batteries?

If the motor will be used without the addition of human power and exclusively on flat ground, then for a 750 Watt motor the gear ratio could be calculated for a 31 MPH top speed. If under these conditions the gear ratio is higher then the motor will lug which will cause it to provide less speed and power, and also to overheat. If the bike will not exclusively be used on flat ground then we recommend gearing it even lower, such as for 25 MPH, so the motor will not lug and overheat when the bike is going up inclines. 

A gear ratio that is too high for the motor will cause a slower than possible top speed and quite possibly damage the motor or controller. If you plan to continuously pedal along with the motor then the gear ratio could be raised to the level that the motor's 750 Watts of power will provide along with the continuous human power that the rider will provide. For example, if the motor provides 750 Watts of motor power, and the rider provides 250 Watts of pedal power then the gear ratio could be calculated for a 1000 Watt motor and a top speed of 30-35 MPH depending on the terrain the bike will be used on.

The minimum battery pack size that should be used with a 36 Volt 750 Watt motor is 36 Volts 10Ah - this would be a battery pack made from three 12 Volt 10Ah batteries. With a 36V 750W motor on full throttle all of the time, a 36V 10Ah battery pack will provide around 35 minutes of runtime, a 36V 15Ah battery pack will provide around 55 minutes of runtime, and a 36V 22Ah battery pack will provide around 80 minutes of runtime. On an electric bike pedaling along with the motor will greatly increase the runtime. Many people who own electric bikes have noticed that by continuously rotating the pedals with a moderate amount of force that the runtime of the battery pack can be doubled. 

Practically all sealed lead-acid electric scooter and bike batteries are 12 Volts and three of these 12 Volt batteries can be wired together to create a 36 Volt battery pack.

We can help with compiling a list of compatible parts for your project or making a kit out of the parts. Please let us know if you have any questions.

I would gladly pedal along with the motor to conserve power and/or improve my top speed, but it's a single speed bicycle geared for start-ups, so the pedals basically become useless over 20 mph. So, based on the information you've provided me regarding wattage, gearing ratios and top speed, perhaps I should go with a 1000w motor and gear it for 35 mph. Item number MOT-361000 appears to be in the rpm range that I want. Do you think it might be suitable for my application? Also, do you carry a battery pack that can power it by itself? I'm thinking of splurging on a lithium-ion battery pack as well, as I prefer not to deal with big clunky lead-acid batteries and/or multiple batteries.

With the proper gear ratio, the MOT-361000 will work very well for an electric bicycle application. We carry an 11 tooth sprocket for bicycle chain item # SPR-B1011 which fits the MOT-361000 motor. 

Every controller for brushed motors that we carry and which we know about have low Voltage cutoff levels that are designed for lead-acid battery packs and not for lithium battery packs. Lithium battery packs have a much wider range of Voltages that they are safe to use with than lead-acid battery packs do. For example, a controller for lead-acid battery packs will have a low Voltage cutoff of 42 Volts while a controller for lithium battery packs will have a 37 Volt cutoff level. So if a controller for lead-acid batteries was used with a lithium battery pack then the controller would shut down before the lithium battery pack was deeply discharged. 

If you want to use a lithium battery pack then we recommend using our MOT-481600BLDC or MOT-481600BLDC-MB 48 Volt 1600 Watt brushless motor along with item # SPD-481600BLDC controller which has a 37 Volt cutoff level. These brushless motors run at a higher RPM than the brushed motors do so a larger wheel sprocket would be required is the only downside.  

If you need an 1800 Watt motor to comply with a 750 Watt maximum power electric bicycle regulation then a Throttle Top Speed Adjustable Limiter with High/Low Speed Switch Connector could be installed between the throttle and controller and adjusted for a maximum motor power output of 750 Watts. This limiter has a connection for a switch which will turn the limiter on and off so the limiter can be turned on when the bike is used on public property and can be turned off when used on private property. 

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