e-Bike Power Compared to Road Bike Power Meter

aplcr0331

New Member
Region
USA
City
Inland Northwest
I'm interested in getting an e-Bike for my wife and am wondering about power. I have a road bike with a power meter so I'm aware of the power output that I'm doing for my rides. Is the power from an e-bike motor the same as the power that I'm producing? I'm guessing a watt is watt is a watt, correct? If I ride at 175 watts for 10 miles and my average speed is 15mph (estimated). Does that mean my wife could ride at 75 watts and the bike would provide an additional 100w assistance (based on level of assist she selected) and theoretically she would go the same speed as me, right?

We have a long climb here that I want to do with my wife. I average about 7-8mph up the climb so it's not like she needs to climb like Ruth Winder to keep up with me. I really would enjoy her company on these rides (she's a classy Dame and even after almost 3 decades together still seems to like my company as well) would a class 1 e-bike with a 250w motor/output allow her to do these longer climbs without too much effort?

Thanks.
 

Timpo

Well-Known Member
The short answer is no.
"Watt is watt" is way too simplified.

That's like saying turbocharged Honda Civic with generating 300 horsepower is same thing as V8 Ford Mustang generating 300 horsepower.
Well, "horsepower is horsepower", but they have completely different characteristics.

Also, I have ridden so many 500W ebikes.
Mid drive, hub drive, (geared hub, direct hub, etc) and they all had different characteristics in terms of assist and power.

I'm not an engineer, so I don't know about mathematical / theoretical / engineering / scientific part of the differences, but in real life, they're all different.
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
Does that mean my wife could ride at 75 watts and the bike would provide an additional 100w assistance (based on level of assist she selected) and theoretically she would go the same speed as me, right?
That is correct with a mid-drive motor. Technically speaking, any mid-drive motor e-bike is equipped with a torque * crank rotational speed = power sensor (because it is necessary to multiply the rider's leg input by Assistance Factor and provide as much of juice to the motor as to make the torque-based assistance promise happen). The point is, e-bike manufacturers are typically unable or unwilling to make the leg power input figures available to the cyclist.

Bosch offers rider's power input meter in the most expensive displays only. Yamaha/Giant does not show the user power figure. Not sure about Shimano. Of the established brands, Specialized have made it the best. You can track the rider's power input on the display, smartphone, a cycling computer or sports wearables. An independent BLEvo app allows you seeing both user leg power and the motor power online during the ride. You can also analyse the power figures post-ride, even on a PC.

So, for the mid-drive motor e-bike, the motor power is added to the chain-ring together with the rider's power input. In your own example, your wife needs 100 W of assistance with her input of 75 W. The amplification factor would be 100 / 75 = 1.33 x. With Giant/Yamaha e-bikes, the 1.25x or 1.50x amplification happens at Assistance Level 2 (Basic). With Specialized e-bikes -- for example Turbo Como 5.0 -- the assistance level would be Specialized 35% (and it is a typical value for the Eco mode - it can be fine tuned).

Hope that helps.
 

aplcr0331

New Member
Region
USA
City
Inland Northwest
That is correct with a mid-drive motor. Technically speaking, any mid-drive motor e-bike is equipped with a torque * crank rotational speed = power sensor (because it is necessary to multiply the rider's leg input by Assistance Factor and provide as much of juice to the motor as to make the torque-based assistance promise happen). The point is, e-bike manufacturers are typically unable or unwilling to make the leg power input figures available to the cyclist.

Bosch offers rider's power input meter in the most expensive displays only. Yamaha/Giant does not show the user power figure. Not sure about Shimano. Of the established brands, Specialized have made it the best. You can track the rider's power input on the display, smartphone, a cycling computer or sports wearables. An independent BLEvo app allows you seeing both user leg power and the motor power online during the ride. You can also analyse the power figures post-ride, even on a PC.

So, for the mid-drive motor e-bike, the motor power is added to the chain-ring together with the rider's power input. In your own example, your wife needs 100 W of assistance with her input of 75 W. The amplification factor would be 100 / 75 = 1.33 x. With Giant/Yamaha e-bikes, the 1.25x or 1.50x amplification happens at Assistance Level 2 (Basic). With Specialized e-bikes -- for example Turbo Como 5.0 -- the assistance level would be Specialized 35% (and it is a typical value for the Eco mode - it can be fine tuned).

Hope that helps.

Nice...this is good information I really appreciate it. I'm probably getting the Cannondale Synapse NEO that REI has on sale which is mid-drive. It's almost identical to my wife's current bike as far as looks/size/geometry. I'll just move the saddle and pedals over from her current bike.

It looks like, according to the Bosch website, that the model of motor on the Cannondale provides assist at the following levels; 40, 100, 180, 270. When you say it can be fine tuned do you mean you can adjust the levels of assist for each mode (in the case of the Cannondale it's Eco/Tour/Sport/Turbo) on the motor itself?

Thanks again for the replies!
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
No, the Bosch motor with Purion display cannot be fine tuned, unfortunately. The 100 or 180% assist should be fine.