Feedback with mid drive motors, heavy bike and Nexus (7)

[Plortus]

Hello,

This is my first post here. I hope I will follow the rules of this forum .

I am considering upgrading my Genesis Smithfield with a mid drive motor.
It's a heavy bike (28kg - 61.73 Lb) and it has Nexus 7 hub.

My typical trip is 10km with 120m elevation gain (6.2 miles - 394 ft).
On the way there, I don't want to sweat at all because I'll meet clients.
There are many stops on the way (traffic lights, roundabouts, etc.). So I'll have a lot of stops and starts.

I have a lot of concerns:
With pedaling sensors (Bafang):
1. Would I need a gear sensor for smooth shifting and no damage to the hub?
2. Can the stops and starts wear the hub? If yes, how to prevent that?

With torque sensors (Tonghsheng):
3. Does it work well without a gear sensor?
4. Will the assist be strong to avoid sweating at all?

Many thanks for your feedbacks.

 

[spinningmagnets]

When pedaling a bicycle with no motor, I always stopped pedaling to shift, and then gently ramp up power when pedaling resumes. That seems to provide a smooth gear-shift.

Ive found that using that technique with ebikes works well too. Some drive types and gear shifters may tolerate more abuse than others, but I don't know what issues would occur with a Nexus-7.

Ebikes have a 5V e-brake circuit, so that when the brakes are applied, the power is cut. The "gear sensors" use a hall sensor next to a magnet on the shift-cable to sense movement, and it cuts power for a moment to reduce shock to the gear-shifting.

 

[Plortus]

Hello spinningmagnets,
Thank you for your answer.
Regarding gear-shift, I'd like to be sure, we have the same thing in mind:
When I shift, I just release the pressure on the pedals so that there is no effort on the transmission when the shifting occurs.
I mean I don't completely stop pedaling, I just slow down.
Would you say this is enough with an e-bike? Or would you have to literally stop pedaling (no movement at all), then shift, then start pedaling again?

Atm, I would prefer the Bafang over the Tongsheng regarding my "no sweat" constraint and the ability to adjust the power map to preserve the Nexus 7?
But I'd like to keep enjoying pedaling my bike specifically regarding gear-shifts...

 

[AHicks]

To build on what spinningmagnets is saying (I think), is many of us are used to shifting multi geared bikes prior to riding our first e-bikes. We're already used to that pause in effort required for a smooth shift. It's a habit most don't even think about. That same habit works just as well when shifting an e-bike.

The shift sensor doesn't change a thing for me. About 90+% of the time I shift, it's pausing at exactly the same time I am. To the point you don't notice it's even there. Other times, maybe when your timing is off a bit, you'll notice it. Big thing in my mind is there is no downside to having one installed.

If shifting is new to you, or it's something you haven't done a lot of, I believe a sensor should be a welcome addition to your rig.

 

[Plortus]

Hi AHicks,
Yes I'm also used to that "pause of effort" during shifting. I used to ride a mountain bike on single tracks with 2000m elevation gain. Good shifting skill is mandatory on those steep tracks .
So it's great to hear that the same habit will have the same effect, I mean smooth shifting. I was wondering if I can save the extra money without risking to break the Nexus.

Regarding the Bafang vs Tongsheng stuff, would you have something to add?
Thanks!

 

[Chalo]

I would be very cautious about putting superhuman power through a Nexus 7. 750W if you're not pedaling in earnest, less if you want to jam on it. Don't use especially low gearing on the chain drive.

 

[Plortus]

Hi Chalo,
Thank you for your feedback.

At the moment I'm planning to use a 250W motor or maybe a 500W.
I read that installing a big chain ring with a small sprocket is a good practice to protect a speed hub like the Nexus.
What do you think?

 

[Chalo]

At the moment I'm planning to use a 250W motor or maybe a 500W.
I read that installing a big chain ring with a small sprocket is a good practice to protect a speed hub like the Nexus.
What do you think?

That power range should be no problem.

Raising the external gear ratio is a good idea, as long as your lowest gear is still low enough to ride the bike without power in your local conditions. Raising the ratio (with a larger chainring or a smaller rear sprocket) not only reduces the maximum input torque to the hub, but it allows you to pedal the bike along with the motor at higher road speeds than you would otherwise be able to.

 

[Plortus]

Thanks again for you answer.
That's very enlightening for me .
I should be able to increase the gear ratio a bit and still be able to ride my bike without the help from the motor.
Anyway, I'll keep that in mind.

 

[Braddudya]

I have a rather heavy bike with a BBS02 and a 13ah 48V battery. It is very easy to avoid breaking a sweat. Its a simple system to install and it just works. For shifting I have found I can just touch the brakes (enough to trip the sensor but not enough to actually engage the brakes) and quite easily shift. You can also get a shift sensor but I have no experience with it.

One of the best parts with the BBS02 is that is it nearly completely silent.

I think you would be very satisfied with this kit.

 

[raylo32]

You can certainly get a no-sweat ride out of Tongshen. Just use the highest assist level. Only caveat is how fast you want to go. For "normal" bicycle speeds you are good to go unless you have long steep hills, and then need to install the passive cooling mods.

 

[Chalo]

You can certainly get a no-sweat ride out of Tongshen.

No sweat, just fractures when it snaps off.

Oh wait-- you will have to sweat when pedaling back to base after the thing dies for one of several likely reasons.

 

[electric_nz]

How about a moderate front hub geared motor? Bafang 500w or similar?

 

[raylo32]

LOL... Not the normal 68/73mm axle TSDZ2. Unless you weigh 280#. It is up to the task for most riders. The longer fat bike version is the problem. Mine hasn't stranded me yet in 2 years, although since I mostly ride pedal bikes, it only has about 1000 miles. And I am in good enough shape to peal it home if needed.

You can certainly get a no-sweat ride out of Tongshen.

No sweat, just fractures when it snaps off.

Oh wait-- you will have to sweat when pedaling back to base after the thing dies for one of several likely reasons.

 

[Chalo]

LOL... Not the normal 68/73mm axle TSDZ2. Unless you weigh 280#. It is up to the task for most riders.

Nope. Its key design flaw was already recognized as a big problem over 45 years ago for the Viscount bottom bracket spindle:

http://pardo.net/bike/pic/fail-001/FAIL-012.html

Note that the Viscount spindle is 17mm in diameter, while the TSDZ2'S is only 15mm. That's inadequate even if it didn't have grooves cut in the wrong places.

 

[raylo32]

Agree there are design issues. But the shorter axles create less stress. I am a very strong 190 pound rider and I haven't broken mine yet. After the reports here I don't stand on the pedals in hard gears anymore, however. For most folks here riding these like an e-bike with reasonably gentle pedaling and letting the motor do the work, they are fine.

LOL... Not the normal 68/73mm axle TSDZ2. Unless you weigh 280#. It is up to the task for most riders.

Nope. Its key design flaw was already recognized as a big problem over 45 years ago for the Viscount bottom bracket spindle:

http://pardo.net/bike/pic/fail-001/FAIL-012.html

Note that the Viscount spindle is 17mm in diameter, while the TSDZ2'S is only 15mm. That's inadequate even if it didn't have grooves cut in the wrong places.