Hub Motor eMTB?

[Leora]

Hey. I currently have regular a mountain bike; I do a lot of riding around the city but do also do a good amount of trail riding. I'm hoping to convert it to electric shortly, sounds like a fun project and hopefully it will get me riding more.

But with pre-built/commercial eMTBs, I always see them using some sort of mid-drive system, never hub motors. My best guess would be that it's either for better torque or due to the fact that rims aren't that difficult to damage on the trails? Regardless, will it be a big issue if I take a hub motor on the trails? I was a little concerned about rim strength, for one. I would probably run slighter higher PSI than I otherwise would, just to be safe.

Furthermore, would any of you have any motor suggestions? I'm wanting to spend less than 500CAD / 400USD. I'm on 27.5" rims and would be looking for between 1KW - 2KW of power. Will probably be using a 52V battery. Any suggestions re geared vs direct drive?

 

[Astro66]

Putting motors in the wheels means your suspension travel is also needing to move all the extra weight of the motor. So the suspension on a hub motor EMTB would be far less reactive.

Also not driving the motor through your gears, means the torque at the wheel would be much less compared with a mid drive, when you are in first gear. So your ability to climb is reduced.

And lastly. It unbalances the bike, having the weight of the motor in the rear or front wheel, compared to having in the middle of the bike, with a mid drive.

 

[Joecrow]

You might also want to bear this in mind before considering a conversion!


Some e-bikes to be banned on most TfL services

Quote:- "TfL drew on its own analysis which it said suggested bikes adapted using electronic conversion kits posed a greater fire risk than purpose-built e-bikes, although it pointed it could be hard to differentiate between modified and unmodified e-bikes."

NB. TfL (Transport for London)

 

[nickf]

My first ebike was a DIY build with a MAC 1500W max rear hub motor mounted into a beefy rim. I fitted it on an old 2003 Orange Patriot to see how it would ride on my local steep and rocky trails. It did OK. But curious to see how a "real" eMTB would compare I test rode a Trek Rail from my local bike shop and it simply blew me away. I ordered one on the spot.

Everything that Astro66 said is correct and I have to admit that my rear hub eMTB experiment might have saved me the considerable expense of buying the Rail if I had chosen to go for a BB-mounted rather than hub motor.

At the time I had considered the Bafang BBS02 or the Tongsheng TSDZ2 which were among the go-to DIY motors that simply fit into the bottom bracket. The Tongsheng has an internal torque sensor, which the BBS02 does not, and as a result gives a more natural ride characteristic.

I have recently used the MAC hub motor on an off-road trike project but despite its massive 1500W power rating it couldn't cope with the demands of moderate trails as it doesn't benefit from the bike's gearing. Having said all that there's an EMBN video where they try out a basic hub-motor eMTB, and as long as you stick to gravel or easy manicured trails it might just be OK for you. But from my experience, whether you go the DIY route or buy a proper EMTB, you will find that a centrally mounted motor is far superior to a rear hub motor bike. YMMV.

 

[Tim1023]

With the budget you mentioned, anything you buy new would likely be a tad dodgy.

You may want to look at second-hand ebikes. Also not without its risks, but you should get more bike for your money.

Re where the motor is, you can get away with a hub motor if you're just riding on roads, but if you're planning on going off-road, you really want the motor where you are peddling, not only because of wanting to minimise unsprung weight, but also because that is where your centre of gravity is.

 

[nickf]

With the budget you mentioned, anything you buy new would likely be a tad dodgy.

You may want to look at second-hand ebikes. Also not without its risks, but you should get more bike for your money.

Re where the motor is, you can get away with a hub motor if you're just riding on roads, but if you're planning on going off-road, you really want the motor where you are peddling, not only because of wanting to minimise unsprung weight, but also because that is where your centre of gravity is.

Agree with all this. You're likely to need all your $500 budget just to buy a decent quality battery! And you shouldn't risk buying cheap Chinese batteries that may use poor quality cells and/or not have adequate BMS protection and be a potential fire hazard. Moreover, whereas a mid-drive motor kit like the Bafang or Tongsheng is pretty much plug and play, you will need to buy a separate controller, display, and pedal assist sensors with all the associated cables if you go the hub motor route. All this adds cost.

Building your own DIY ebike can be a fun project if you have the necessary technical understanding and skills. But I agree with Tim1023 that you could get a better bike for your money by buying a 2nd hand eMTB, especially in the current market where 2nd hand prices are really low. Lots of great deals to be had if you look around.