Power reduces nearing limiter.

[Wodger63]

I have done a lot of reading on this forum and in other places but it's hard to get a definitive answer.
Little bit of history, previous to my Trek with the Gen 4 I had a Giant with a Yamaha PWX @ 80NM.
By all reports the Gen 4 @ 85 NM is meant to be a kick ass motor and I assumed it would feel stronger than my previous Yamaha.
I still have the Giant and it is now ridden my GF, she now thinks she is a cycling goddess and the worst thing is I can't catch her on the flats without making a huge effort.
Weight and aerodynamics aside, I ride 200klms per week, she would be lucky if she did 50klms in a month and when we rode analogue bikes together I needed to constantly wait for her, so it's not fitness.
I have swapped between the 2 bikes a few times but it's a PIA swapping seats around, setting heights and losing your setup trying to get comfortable again.
It would seem from the seat of the pants and GPS that the Yamaha is a couple of kph faster before it hits the limiter at 26-27 kph and secondly the Yamaha delivers full power right up to the cut off.
The Gen 4 on the other hand seems to be tapering off at about 22 kph and by the time I hit 25 kph it's all over red rover.
Speed is measured by GPS on a Bryton 420 and confirmed by my Fenix 6 pro, Purion is telling me near on 28 kph.
This is not a problem so much off road in Tour where I ride most but when I hit Turbo it is really pronounced.
I returned to the LBS to confirm I had the latest software and 85 NM, which they did.
Anyone care to comment on their experience, is the Gen 4 just a mid range engine for punching up steep inclines, because it feels like the closer I get to the limiter the more gutless it gets.
Would a derestriction chip fix my issue, I'm not looking to go way faster than 25 kph, it just feels that the motor is giving up just before I hit that nice cadence/cruising speed on the way from a ride.

 

[Zimmerframe]

G-Day !

The Gen4 tapers off the power as you get towards the limiter. On GPS, this normally coincides with a speed of 25kph. On the Purion, it shows 27.x. From the Purions perspective (as in what you see), it just tapers off the power so you don't get that horrible STOP you get with some motors which makes it a lot harder to carry on pedalling over the assistance point. For me, I find it far easier to ride the Bosch over the assistance than the other motors because of this gentle "hand over" - where your body has time to adjust and start taking over the load.

As for why the Purions generally show about 2.5-3kph or 2mph more before the full assistance stops, I'm not sure, maybe to comply with the legal restrictions of the real speed being 25kph/15mph - whilst still giving the rider the feeling that they still get to 25kph then the assistance tapers. For me, I like it as it is. It also means that once you get used to it you can ride more or less on the limit and not be using much power, so cover big distances whilst still being helped just enough.

One thing you might be suffering from is a lack of cadence. The Yamaha motor seems to encourage a lower cadence as it still gives you lots of assistance. With the bosch, if you want lots of assistance at higher speeds, you have to be also putting in some power - ideally with a higher cadence - then the motor really delivers.

You'll read of several people saying they feel like the motor is holding them back once they get to the limit, invariably, it's people with a low cadence, so when the assistance stops, it feels like you're trying to pedal a 200kg bike with tractor tyres up a vertical slope, because ultimately, it's still a 25kg bike with high drag tyres doing 15mph/25kph and the rider's hardly putting any (relative for what's required) effort in, so the assistance stops and suddenly you have to do it all yourself.

Something like a volspeed would enable you to tune the taper off point a couple of kph quite easily. Or just enjoy riding behind your GF, it's normally not an unpleasant experience.

 

[RustyIron]

she is a cycling goddess and the worst thing is I can't catch her on the flats

Darn! Ain't it a bitch when you're slower than the ladies and the old men?
At least you still have your good looks... if that's any consolation.

P.S.
I'd be surprised if any top tier motor manufacturer didn't ramp down the level of assist as speed approaches the cut-off. Instantaneous on/off would create a strange riding experience.

 

[Wodger63]

G-Day !

The Gen4 tapers off the power as you get towards the limiter. On GPS, this normally coincides with a speed of 25kph. On the Purion, it shows 27.x. From the Purions perspective (as in what you see), it just tapers off the power so you don't get that horrible STOP you get with some motors which makes it a lot harder to carry on pedalling over the assistance point. For me, I find it far easier to ride the Bosch over the assistance than the other motors because of this gentle "hand over" - where your body has time to adjust and start taking over the load.

As for why the Purions generally show about 2.5-3kph or 2mph more before the full assistance stops, I'm not sure, maybe to comply with the legal restrictions of the real speed being 25kph/15mph - whilst still giving the rider the feeling that they still get to 25kph then the assistance tapers. For me, I like it as it is. It also means that once you get used to it you can ride more or less on the limit and not be using much power, so cover big distances whilst still being helped just enough.

One thing you might be suffering from is a lack of cadence. The Yamaha motor seems to encourage a lower cadence as it still gives you lots of assistance. With the bosch, if you want lots of assistance at higher speeds, you have to be also putting in some power - ideally with a higher cadence - then the motor really delivers.

You'll read of several people saying they feel like the motor is holding them back once they get to the limit, invariably, it's people with a low cadence, so when the assistance stops, it feels like you're trying to pedal a 200kg bike with tractor tyres up a vertical slope, because ultimately, it's still a 25kg bike with high drag tyres doing 15mph/25kph and the rider's hardly putting any (relative for what's required) effort in, so the assistance stops and suddenly you have to do it all yourself.

Something like a volspeed would enable you to tune the taper off point a couple of kph quite easily. Or just enjoy riding behind your GF, it's normally not an unpleasant experience.

I do understand the drag big tyre weight transition from assistance to no assistance and the extra effort required.
Under good conditions I have exceeded (peddled) well over 35 kph so I am well aware of the effort required once assistance stops.
(it is hard to maintain for any length of time)

If I didn't have the Giant/Yamaha to compare to I would not know any different and when I'm by myself it becomes a non issue.

Funnily you mention cadence, with my current gearing I find myself in that situation when on the flats where one gear is too high and the other too low.
I will take more notice of cadence v engine response in up coming rides but TBH I think it just the nature of the Gen 4 and that I prefer the Yamaha motor characteristics.
As for riding with the GF, she only wants to ride bike paths and bails out when it comes to the more off road techy stuff which I prefer.

 

[Expidia]

Older post, but I figured I'd comment because I currently own both a Trek with a 2022 Bosch Performance CX 250 watt 85 Nm and a 2021 Giant with their Yamaha SyncDrive LifeGiant 250W 80Nm motor.

I talk in mph as it's easier for me. I put around 440 miles on the Giant in the first month and the handoff after it's assist up to 28 mph was very smooth. A month later I bought the Trek and as soon as I hit 20 mph it's like a heart punch where the Bosch motor seems like it just stops in mid flight (as the assistance just abruptly just disappears).

I attributed this to the design of the different motors and also the Trek Powerfly has 2.4 mm tires that are knobbier than the 2 inch tighter tread gravel tires on the Giant which are closer to road bike type tires.

The Bosch has an instant dead spot hit of drag at 20 mph with their draggier Trek Bontrager tires. I can get it over 20 mph on the flats, but that comes with a lot of effort on my part. With the Giant Yamaha motor the transition over 28 mph was a lot less noticiable. So much so that after a few weeks I went on a quest to put similar 2 inch gravel type tires that came with the Giant to get less road resistance on the Trek Powefly.

Turned out to be a bad idea as cornering on especially damp surfaces was down right dangerous and I was not getting less road drag anyway . . . so I went back to the OEM Trek 2.4 wide tires and I've grown to really like them on all types of terrain.

@Zimmerframe comments were right on the money from my experiences with both e-bikes and the two different brands of motors. He had interesting comments as to it's all about cadence and that's something I'm going to work on during my next rides with the Boach motor.

But I know exactly the feeling the OP is describing with the Bosch. You are peddling away at 19 mph and then all of a sudden it like a WHUMP to your heart at exactly 20 mph. I've read users complaining about this sucky Bosch transition in other reviews, threads and forums. But everythings a trade off as these same reviews give the Bosch motors kudos for their low end torque over the Yamahas.

Update: Tested the Bosch yesterday (20 top). Frustrating that it starts it's handoff around 18 mph. From the last time I used the the Giant . . . the Yamaha motor (28 top) does not start it's handoff at 26! Transition was very smooth.