Author Topic: Bafang PAS senso  (Read 1855 times)

lamonabike

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Bafang PAS senso
« on: June 27, 2026, 10:31:50 PM »
Hi. Has anyone recently converted their Rohloff-equipped Thorn with a Bafang front motor?
There’s a couple of issues Id like to understand.

The online sales stores (Amazon, etc) offer a left side and right side PAS sensor, neither of which seem very compatible with Thorn’s BB. Has someone fitted either of these successfully?

Also the Thorn dropouts are 9mm. I can’t tell but I imagine the Bafang kit requires 10mm. Has anyone successfully installed this and what was the solution?

Thanks!

Andyb1

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Re: Bafang PAS senso
« Reply #1 on: June 28, 2026, 06:45:52 AM »
On my wife’s hybrid I had to file the front fork dropout to 10mm to take the hub motor axle.   Could you find an older / cheaper fork?

lamonabike

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Re: Bafang PAS senso
« Reply #2 on: June 28, 2026, 02:18:44 PM »
Thanks. Could do yes. I’d rather avoid either!

Filing down is something I could live with.
I’m less convinced that the PAS sensor will fit and there doesn’t seem to be a way to check

Danneaux

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Re: Bafang PAS senso
« Reply #3 on: June 28, 2026, 04:55:20 PM »
Rather than modifying the fork, I'd be inclined to try filing flats on two sides of the axle, where it protrudes past the bearing locknuts. If you measured carefully to make sure they were in the same plane side-to-side, I think removal of only the threads (0.5mm each side) would fir the dropouts while still leaving adequate full threading for locknuts.

Best, Dan.

Andyb1

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Re: Bafang PAS senso
« Reply #4 on: June 28, 2026, 08:40:20 PM »
The axle reacts the electric motor rotation and it is imperative that it can not spin in the fork (or the wiring will twist badly and get wrecked).  ‘Torque brackets’ are available in stainless steel on ebay that go on the axle and bolt to the mudguard stay holes, but are probably only made for a 10mm axle.

lamonabike

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Re: Bafang PAS senso
« Reply #5 on: June 28, 2026, 08:59:28 PM »
Thanks all.

How about the PAS sensor. Has anyone got it to work on a Thorn using either the left or right side version?

lamonabike

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Re: Bafang PAS senso
« Reply #6 on: July 08, 2026, 06:03:38 AM »
I thought you might be interested to hear the latest on this.
I bought a left handed PAS sensor for £12 or so and installed it on my Thorn Raven crank.
It went on okay but as I was installing the crank arm back on it felt like I was crushing the sensor.
Just been out for a short ride and the turning of the cranks feels different.
I’m still not convinced it will all work but I think I just need to go ahead and buy the full kit and see what happens.

lamonabike

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Re: Bafang PAS senso
« Reply #7 on: July 08, 2026, 06:04:34 AM »
Photo of the PAS sensor

Andre Jute

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Re: Bafang PAS senso
« Reply #8 on: July 08, 2026, 07:19:33 PM »
There's a clearer photo of the sensor, and its receiver, in my 2012 set of articles Building an Electric Bike, which deals with fitting a Bafang front-drive motor and its control elements, starting at
https://www.coolmainpress.com/BICYCLINGbuildingpedelec1.html
The second article
https://www.coolmainpress.com/BICYCLINGbuildingpedelec2.html
contains the clearest photo of the sensor and receiver:
https://www.coolmainpress.com/miscimage/pedelec/133%20pedelec%20Ekit_Sensor.jpg[/img]]

Note that while I left off the sensor and its assorted electronics as counterproductive to my intention on hand of advice from my local police here in Ireland, in Britain fitting the sensor may be a regulatory matter depending on the intended use of the bike. (On my current installation of a Bafang centre motor on my everyday bike which is not a Thorn, the sensor and its receiver are both internal.)
« Last Edit: July 15, 2026, 05:44:23 PM by Andre Jute »

lamonabike

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Re: Bafang PAS senso
« Reply #9 on: August 03, 2026, 09:53:35 PM »
Okay so I’ve installed the Bafang motor!
Not without messing a few things up that ended up costing me an extra £200. But that’s still a lot cheaper than the Cytronex and other kits which have a lot less torque.

My crank fell off a few days after I installed the right hand PAS sensor so that doesn’t work. I do have the left hand sensor but haven’t bothered to try it yet. Am just using the thumb throttle (yes, yes, I know).

At the time of buying/ writing, Bafang doesn’t give you that much in the way of instruction. So if you’re a bit of an idiot like me you can make some silly mistakes.
I may write a bit more later.
The main thing I learnt is that you absolutely need to put torque arms on your forks otherwise the motor will spin out of the forks (even a centrimeter or so) which pulls the cable and destroys the connection. I had to buy a new motor.

However it works well now and the hills of Lewes are manageable even on the lowest setting.
I have Andre Jute to thank for writing about the level of power/torque you need.

Pictures later.

lamonabike

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Re: Bafang PAS senso
« Reply #10 on: August 03, 2026, 10:00:55 PM »
This is what my loaded rig looks like (minus a 5 year old and some panniers).

Andyb1

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Re: Bafang PAS senso
« Reply #11 on: Today at 12:34:03 PM »
Please check the current law incase I am wrong, but my understanding is that in UK when adding an electric motor to a secondhand bike then a PAS is not needed and just a thumb throttle is fine.
On a new ebike I think it is mandatory.

I never fitted a PAS to my wife’s hybrid - and like that she could start by just using the thumb throttle.  Which at times (upslope, in too high a gear) could be very useful.

Andre Jute

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Re: Bafang PAS senso
« Reply #12 on: Today at 04:13:45 PM »
At the time of buying/ writing, Bafang doesn’t give you that much in the way of instruction.

That's true of almost every Chinese manufacturer and was true nearly twenty years ago when I first fitted a front motor. It may be that they deal mainly with OEMs aka bike manufacturers, who don't need instruction. And, of course, Chinese mainland consumers have no consumer rights -- if they bollox the kit, if it is broken in transit, if it is a Monday morning hungover job with bits missing or broken, in all cases it is their fault, not the manufacturer's liability. It's one of the reasons I bought my kit from a British supplier, Asian of some denomination, who had made instructions of their own for the 8FUN strain of Bafang, which was refined in Switzerland (I kid you not) for the sensitivities of Western consumers -- still without the slightest thoughtvc`zas≥/ by Bafang of providing instructions. The instructions weren't up to the standard of those I once wrote for a Belgian manufacturer of electronic kits, but if you knew a little about electricity, you could busk your way through.

I have Andre Jute to thank for writing about the level of power/torque you need.

My pleasure. One of the good things about this forum is that so many members give credit where it is due.

Hurrah for you getting it working.

I never fitted a PAS to my wife’s hybrid - and like that she could start by just using the thumb throttle.  Which at times (upslope, in too high a gear) could be very useful.

I not only live up a steep hill, I live on a steep hill. Starting out for the countryside on this side of town is uphill, so a throttle is more than just useful, it is essential because the whole pedelec legal concept, designed by German lawmakers who were actively hostile to cycling (Germany lived by automobile exports until the Greens wrecked their country so that there is no electricity to keep the factories running), is counterproductive to real life cycling, where you need more assistance when starting up, not less, but the pedelec gives you less when starting up, and on a hill, and when you're heavily loaded, less and less as your legs get tired. Ugh!