New QS138 90H V3


100 kW
Looks like QS has a new option for the 138 V3 “90h” The new 90h now has a gear reduction similar to the the 70h V3.


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10 W
I like it. I wonder how much power these can take for bursts.
I have a "4000W" QS hub motor in my Vespa. It tolerates several second long bursts up to 15,000W.

If I had the free time, I'd love to put this motor in a Ninja 250 or similar sized motorcycle.
I am really curious what this can handle in bursts. I have done a conversion on an rm 125 and a kx 85 with QS 138 70H V3 motors and I make 16,800w not accounting for losses when at 84V & 200 battery amps. Even doing 0-60mph drags up and down the dirt road repeatedly, going through deep sand etc. I’ve always been able to hold my hand on the motor only to pull it off out of boredom. So my guess maybe 130-140 degrees Fahrenheit. I remember reading a post saying the 138H should be able to handle up to 30% more power (makes sense based on the most simple of maths).

Did anyone also see that there is a reduction geared version of the QS 165 60H coming out as well? See pic below sent by Vito Ho at SiAECOSYS.


Off topic from here, maybe I should start a new thread?

I would really like to push the 138 90H motor to the limit with a fardriver ND96850 but maybe that is being way too ambitious.

Would love to make as much power as the starkvarg with a diy build. 450A battery with fully charged 24S pack would give me 60.8hp granted without electrical and mechanical losses, but I somewhat doubt they are factoring that into their marketing campaign either.

Any thoughts? Maybe I have to go for that 165 60H but by simpleton maths that shouldn’t be capable of anymore power than the 138 90H…I think… really dreading having to do the 180 90H as it takes up more space, more money, and I’d have all the extra fab work of a primary reduction *sigh*, but would be a lot more confident that it would get the job done.


Staff member
More options are a good thing. The "H" is the height of the magnet (its height if a hubmotor is laid on its side, don't ask me why).

If we are talking about a motorcycle kit that has the motor mounted cross-wise, with a chain/sprocket with one run between motor and wheel (which is the common orientation)...we might call the H-number the width of the motor stator in millimeters.

The 138/165 is the diameter of the cylindrical stator in mm. In some applications, the larger diameter motor will fit, and if it does, it will make more torque from the same amount of input watts.

You want to start any conversion with a motor that is as large as possible. Once the diameter and length are maximized to fit, then you can determine how many watts can be fed to it.

The factory 2:1 gear reduction is also very valuable, because without it, you may be forced to have one of those huge sprockets on the rear wheel. That wouldn't be horrible, but when it comes to replacing a worn sprocket or changing the tooth-count...a "normal sized" sprocket provides the best selection and lowest prices.


1 kW
I use this motor without the gearbox at 25 kW peak.
Someone on the forum is using the 35kW peak gearbox version.