750 watt vs 500 watt motor

[DragNLady]

I am planning to buy a trailer to pull on my bike. The weight of the trailer and person will be 200 pounds. I will only be pulling the trailer on the rail trail, flat terrain, no hills, no streets to cross. I will be getting a RAD City Step-thru with 48v and 14 amp. and a direct drive hub motor. Will a 750 motor make a big difference as compared to a 500watt motor? It will cost me $400. more for the 750 watts. Is it worth it? If so, how will the 750 watt outperform the 500? I know the watt hours are the most important aspect of choosing a bike, but I cannot find that much information on whether a 750w motor would be that much better than a 500w motor. What advantage would a 750 motor give me over a 500 motor? Thanks!

 

[rich c]

I am planning to buy a trailer to pull on my bike. The weight of the trailer and person will be 200 pounds. I will be getting a bike with 48v and 14 amp. Will a 750 motor make a big difference as compared to a 500watt motor? I will be riding on mostly flat terrain, no hills. It will cost me $400. more for the 750 watts. Is it worth it? If so, how will the 750 watt outperform the 500? I know the watt hours are the most important aspect of choosing a bike, but I cannot find that much information on whether a 750w would be that much better than a 500w. Thanks!

Watt hours is just the capacity of the battery. Not the most important factor in buying an eBike. Both those motor numbers are a nominal rating, not the max. Also the manufacturers can put any number they want. My 350 watt Haibike pulls better than a 500 watt Bafang hub motor. The programming in the controller also comes into play. The motor only responds to how much energy is sent to it. Experience related information is the only true evaluation. Not numbers on a sales page.

 

[DragNLady]

I am confused. I have read on many different sites that the battery capacity in watt hours is the most important factor to consider when buying a bike.

 

[JRA]

I seriously doubt that spending $400 more for the 750w bike will be worth it. Even without knowing exactly what motor type we are talking about the difference between the two is down to the amount of Amps coming through the controller basically. On flat ground and not expecting to go really fast the 500w should be sufficient. I would check to see that it is a geared hub motor if in fact it is a hub motor you are considering though.

And yes wh's are important for range requirements. Also if you are going to be pulling a load you will be using more wh/mi than a lighter bike, once again dependent on how much you are asking of the system. At 672wh's your battery is above the average of 500wh batteries so it should be fine.

 

[Justin Fischer]

I am confused. I have read on many different sites that the battery capacity in watt hours is the most important factor to consider when buying a bike.

That is very important, I think, but you may be confusing the nomimal power output of the motor (500w vs 750w) with the watt hours of the battery (capacity) So a 48v x 14Ah battery = 672 Wh, no matter what kind of motor you have it attached to. Personally I think upgrading to a 52V and close to 900Wh pack would be a better use of $400, if you can.

Then the controller matters too, if the controller can handle it. A controller's maximum power output to the motor is multiplied by the voltage of the battery. For instance my 52V CCS has a 20amp controller. Fully charged the pack is 58.9v x 20A = 1178 watts to the "750W" motor. This cuts off at 28mph, but if you're hauling something, or going uphill, higher voltage from the pack would be a big factor.

 

[Deleted member 18083]

I am confused. I have read on many different sites that the battery capacity in watt hours is the most important factor to consider when buying a bike.

My choice…

1. 500 watt versus 750 watt motor:
   I'd save $400 and choose the 500 W motor because I doubt that I'd ever need the 50% extra power.
2. 500 watt hour versus 750 watt hour battery:
   I'd spend the extra $400 and choose the 750 Wh battery that would give me 50% extra distance.

 

[jazz]

Power = battery voltage x controller amps. That gives a true indication of power not necessarily the motor wattage. So if you have a 500w motor and 750w motor and both are running a 48v battery and stock 20amp controller they are essentially putting out close to the same wattage most of the time.

 

[rich c]

I am confused. I have read on many different sites that the battery capacity in watt hours is the most important factor to consider when buying a bike.

If all you do is ride distances of 40-50 miles, bigger batteries may be required. Most of my rides are in the 10 mile range, with frequent 20 miles rides. If you do those distance of rides and pedal like a bicycle, save the weight and get a smaller battery. If you intend to ride the eBike like a moped and ride throttle only, then big batteries are required. Riding style dictates battery size. No universal law that biggest is best.

 

[indianajo]

Watt hours is range. Like fuel tank size on a car.
Watts is how much air resistance or weight carried uphill the motor can withstand.
I have two 48 v "1000 watt" hub motors. Controllers are 48v 26 A rated. Both can start me bike & supplies at 330 lb gross weight on a 15% grade. You sound as if you don't have 15% grades in your area.
Torque multiplication matters in comparing motors. Mid drives have an internal gear that allows the motor to spin faster than the crank, and use the sprocket set of the bike, which allows more starting torque but wears out the chain. Geared hub drives have internal gears allowing motors to run at more efficient high speeds. Direct Drive motors have no gears, so high wattage is important in those to start up steep hills. I have DD and geared hub motor. I bought 17.5 AH battery (840 wh) as I hope for 80 mile round trips, 40 with me pedaling unpowered, 40 with the motor doing all the work.
I suspect your trailer produces a lot of air drag. That chews up watt hours, shortening range versus light weight hunched over head first riders. My pannier bags cause some drag, but possibly not as much as a trailer since they are right behind my legs.

 

[Off road all day]

I am confused. I have read on many different sites that the battery capacity in watt hours is the most important factor to consider when buying a bike.

You have not stated if it's a mid drive, shiftable, hub drive or frame drive. You want the maximum , pulling 200 lbs plus the bike and you, 1000 watts for safety. How far are you going?
Watt hours are important for range not power. For increased range and power you need a BIG battery and go to a 60/72 volt motor.. By the end of it the bike

 

[AHicks]

I'm not sure about how you feel about it, but when I point my bike at the opposite side of a busy intersection and tell it to go, I want to get to the other side as quickly as possible.

For that reason, given a choice between 500 and 750 watt motors, this is a no brainer. When adding a trailer to the decision, that makes it even more of a no brainer.

When acceleration or hill climbing is no issue, lets's say the 500 watt motor pulls XXX amount of power at 10mph (due to the factors in play at the moment).

Same identical bike, same identical factors in play as the earlier 500 test, but with a 750 watt motor at 10mph, still pulls XXX amount of power as it's doing the same amount of work the 500 was doing. The 750 watt motor is only using 500 watts! Kinda like the throttle isn't open as far as it was on the 500

The difference between the 2 is the increased amount of power available with the 750 - when or if you want it, and yes, when the 750 is going faster or pulling harder than what is available with the 500 it WILL be pulling more power. In simplest terms, 750 watts vs. 500.

 

[DragNLady]

My choice…

1. 500 watt versus 750 watt motor:
   I'd save $400 and choose the 500 W motor because I doubt that I'd ever need the 50% extra power.
2. 500 watt hour versus 750 watt hour battery:
   I'd spend the extra $400 and choose the 750 Wh battery that would give me 50% extra distance.

… David

Thank you David, but I don't understand what you wrote. I am pretty simplistic when it comes to understanding anything about e-bikes. (I race a dragster, but all I know about the car is HOW to race it, my mechanic takes care of all the rest). I don't know much about e-bikes either, except how to ride it. LOL. It is the motor I am talking about. I assume the batteries will be the same on both bikes? I will be buying a RAD, just don't know whether to get the 500 w or 750 w. I don't want to spend the extra $400. if I don't really need to. But pulling a 200 pound load, I don't know if the 750 w would be better than the 500 watt.

 

[DragNLady]

Power = battery voltage x controller amps. That gives a true indication of power not necessarily the motor wattage. So if you have a 500w motor and 750w motor and both are running a 48v battery and stock 20amp controller they are essentially putting out close to the same wattage most of the time.

Thank you for your reply. I need to know WHY someone would buy a 750w vs a 500w then. What is the advantage???

 

[DragNLady]

I seriously doubt that spending $400 more for the 750w bike will be worth it. Even without knowing exactly what motor type we are talking about the difference between the two is down to the amount of Amps coming through the controller basically. On flat ground and not expecting to go really fast the 500w should be sufficient. I would check to see that it is a geared hub motor if in fact it is a hub motor you are considering though.

And yes wh's are important for range requirements. Also if you are going to be pulling a load you will be using more wh/mi than a lighter bike, once again dependent on how much you are asking of the system. At 672wh's your battery is above the average of 500wh batteries so it should be fine.

Both bikes are Rad City Step-thru.

 

[DragNLady]

I seriously doubt that spending $400 more for the 750w bike will be worth it. Even without knowing exactly what motor type we are talking about the difference between the two is down to the amount of Amps coming through the controller basically. On flat ground and not expecting to go really fast the 500w should be sufficient. I would check to see that it is a geared hub motor if in fact it is a hub motor you are considering though.

And yes wh's are important for range requirements. Also if you are going to be pulling a load you will be using more wh/mi than a lighter bike, once again dependent on how much you are asking of the system. At 672wh's your battery is above the average of 500wh batteries so it should be fine.

Thanks for your reply. It is a direct drive hub motor.

 

[DragNLady]

You have not stated if it's a mid drive, shiftable, hub drive or frame drive. You want the maximum , pulling 200 lbs plus the bike and you, 1000 watts for safety. How far are you going?
Watt hours are important for range not power. For increased range and power you need a BIG battery and go to a 60/72 volt motor.. By the end of it the bike

The RAD has a DD hub motor. When I am pulling the trailer with my 90 year old mother in it, I will not be going far. I would guess 20 miles. Without the trailer, I will be riding 50 miles, most of the time in PAS 1. (But I just rode a century ride two days ago and want to do more of them. I needed 11 bars, so 2 batteries were not enough.)

 

[John from Connecticut]

Thanks for your reply. It is a direct drive hub motor.

Hello, I don't know if this is helpful or more confusing, but here goes. I have two eBikes. Both have Bosch motors mid drives,
a 400 and a 500 watt battery and Identical controllers. I flip flop the batteries all the time and feel no difference in response based
on the battery.

One bike is a commuter the other a Mtn. The gearing on both is similar. The difference in feel is in the motors. One has
63Nm of torque (commuter) and the other has 75Nm (mtb), and that difference and the slight gearing is significant. The bike
will climb a 'brick wall' because of the different motor. My commuter bike is built for speed and doesn't have the
same hill climbing ability.

The Rad City Step-Thru motor has 40Nm of torque and I'm guessing is designed for cruising and speed vs pulling carrying a load. I don't
know for certain, nor am I familiar with the torque characteristics of a direct drive motors vs a mid drive like mine. Someone with
a lot more knowledge can comment.

 

[Feliz]

As pointed out earlier, it doesn't matter what motor you have it depends on the battery and controller! Battery voltage times controller amps V x A = W. For example, my stock Radrover put out 500 watts. I changed my controller to 35A and with the 48 volt battery I'm running three times the wattage ( 35X48=1680 but my controller is limited to 1500 watts. That makes riding safer and more fun. I've done similar things to some of my other low powered bikes.

 

[Alex M]

I wasn't aware that RAD offer their City in reduced speed configuration for Canada. Could be due to some Canadian red tape, and then you don't have a choice. Motors are likely the same, the speed is limited by controller. But, if you do have a choice btw 750W DD City and 500W DD City, there is no sense getting 500W DD version, especially with heavy trailer in mind.

As noted by others, watt-hours are a measure of battery capacity and have little to do with motor. Motor power is in watts. More watts - more pull, or more speed. More watt-hours in battery - longer range.

So which one are you talking about - 500W motor or 500WH battery?

 

[AHicks]

I think you missed jazz's point.

In your post, you said things like "500W motor" or "750W motor" which made us feel that you're thinking the power was determined by the motor.
However, it's NOT the case. It's the speed controller that's sending more energy to the motor.

Juiced Bikes for example, they have had several lineups, 350W motor, 500W motor, 650W motor and 750W motor. (They have 1000W and 1100W HyperFat but those are different)

Anyways, what's the difference between those 350W to 750W motor? Nothing.

Though I agree that often the same motor will have different ratings due to the power available to it, that's not always the case. The geared 750w hub that Rad uses, as compared to the "real" 750w motor that carries a 750w rating from Bafang, obviously are not the same motor for instance (a fact made pretty obvious in one of Bolton's videos). A DD hub with a larger diameter and wider rotor will have more torque than a smaller one even if they are rated the same. This is getting into a level of detail that's likely well beyond the scope of this question, but for my money, bigger/higher wattage is nearly always better.