Question about Newton Meters

[Dfstarman]

What is the difference/significance between a 250 W motor with 80 NM of torque vs a 350 watt motor with 50 NM of Torque?


Thank You

 

[Sonoboy]

Gearing, basically. You could take two identical wattage motors, add different gear reduction to each, and get two different torque outputs. So, if you start with an 1800 rpm motor driving a 10:1 gear reduction drive train, the output speed is reduced to 180 rpm, and the motor torque is increased. The same motor with a 5:1 reduction would produce 360 rpm, but with less torque produced. It’s standard in industrial circles to refer to a motor with an attached gear train as a gearmotor.

Keep in mind that all ebike ‘motors’, with the exception of direct drive motors like the Stromer has, are actually gearmotors. Each type (center drive, geared hub, direct drive hub) has advantages, and capabilities overlap among all threee.

If the lower wattage motor serves your particular needs, it will be the more efficient of the two. If however, you want a speedy bike, and still want enough torque to aid in climbing that very steep hill you encounter in your daily commute, the higher wattage version might be the one you should choose. But don’t be deceived by numbers alone.

 

[Dfstarman]

so if you are evaluating an ebikes with midrives and one is 350 watts with 50 nm and one is 250 watts with 80 nm which would you choose and why?

 

[harryS]

If it's a completed bike, best to test ride. I might believe the ratings if published by a Bosch or Yamaha. If done by some importer out of China, the first liar hasn't got a chance.

Watts is really quite arbitrary too, when it's stamped on a motor. Euro laws are so restrictive on power ratings, I suspect everyone gets their engineer to say "yup",that's 250W" , when it is really a lot more. I wouldn't have said this two years ago, but if a Volkswagon is willing to cheat, you cannot trust anyone.

Without anything else to go by, with my engineer hat on my head, I'd always want more data. Which mid drives you lookingat?

 

[rich c]

You would also have to look at maximum wattage. The Bafang 350 watt motor on my Sondors puts out nearly 600 watts under full load.

 

[harryS]

After noting what bikes you were considering in your other thread, DFstarman, I don't think the specs matter that much as to whether the bike lets you be comfortable.

For range/performance, maybe tilt toward anything with 48V?

 

[Dfstarman]

I guess I will just have to try them to be sure.
I suppose I knew that at some level.

Thanks for all the responses.