Bosch motor cx inhibiting speeds above 20mph

[Rail7David]

I have a 2020 Trek rail 7 with a Bosch cx motor. If I attempt to pedal above 20mph it seems as though the motor inhibits my pedaling. If I turn the motor off I can more easily increase my speed above 20mph when pedaling. Is this normal?

 

[Akelu]

It's normal for the motor to shut off at 20mph, thats the limitter kicking in.
Previous ebikes had a big problem with going over the speed limit like it feels like theres a 'drag' on your pedalling, however the bosch cx gen 4 motor is one of the first motors that mostly 'solves' this problem (but still there to some degree). However compared to a normal bike, a bosch cx gen 4 ebike will feel a bit 'draggier' when pedalling over the limit. If its really intense drag, its probably not right and maybe check out another bike to see if doing same thing or take it back to dealer. But a little bit is normal.

 

[Gyre]

You're saying that above 20 mph, you feel a difference in pedaling resistance between OFF mode and any of the powered modes? Are you getting that same impression with all four powered modes?

 

[Zimmerframe]

I have a 2020 Trek rail 7 with a Bosch cx motor. If I attempt to pedal above 20mph it seems as though the motor inhibits my pedaling. If I turn the motor off I can more easily increase my speed above 20mph when pedaling. Is this normal?

As they said .. and

When you say off, you mean you're actually powering the bike off of just pressing "-" until you're in no assist, ie one mode less than Eco.

It could be that your motor isn't disengaging. The Gen4 Bosch is normally pretty easy to pedal once you're over the assistance limit and doesn't/shouldn't require you to change modes/power off to achieve that. It's still a bit strange that you then find it easier with no power as if their's a hardware fault, you'd imagine the motor would be engaged if it's powered on or off.

Just so we understand. To emulate this, do you start riding with the bike turned off/in mode 0 and then ride upto 25mph ? or do you ride with assistance to 20mph when the assistance stops and then turn the power off to find it easier ?

 

[Rail7David]

Thanks for your thoughts and questions. To be more precise, the motor drag I experience is in the "no assist" mode. I have only noticed the drag while in "tour". I will try the other assist levels and post my experiences. I was using "tour" assist to reach 20 mph and kept pedaling on a slight downhill and could only get to 22mph then switched to "no assist" and could reach 27mph with much less effort.

 

[Hamina]

Remove the chain and check that the motor resistance feels reasonable. Shouldn't be much in GEN4.

If it's somehow speed dependent then it might be a real problem.

 

[Gyre]

For what it's worth, I tried switching through all the modes today while pedaling comfortably above 20mph on my Bosch CX gen 4. Didn't notice any difference at all.

 

[Rail7David]

I tested my Bosch CX gen 4 yesterday on the same slight downhill section of dirt road. The results didn't matter if I was on "no assist", eco, tour, emtb, turbo, or shut off. I found that once I reached 20mph I experienced drag from the motor until I pushed through to above 22mph and then the drag seemed to cease. It was not easy to push through to above 22mph. It feels like slight braking has been applied. Sounds like a trip to the LBS especially after the "no difference" response I received.

 

[bennyuk]

I just demoed a trek rail 7 and the resistance when getting to 20mph (on flat road) was VERY noticable. Didnt manage to push through the drag, but it shocked me. Is this usual on emtbs? (thinking of getting trek rail 7)

 

[Gyre]

I just demoed a trek rail 7 and the resistance when getting to 20mph (on flat road) was VERY noticable. Didnt manage to push through the drag, but it shocked me. Is this usual on emtbs? (thinking of getting trek rail 7)

More resistance than driving an acoustic MTB is normal. It's a matter of degree. If I was to put a number on it, I'd guess about 30 watts worth of drag.

 

[Hamina]

I just demoed a trek rail 7 and the resistance when getting to 20mph (on flat road) was VERY noticable. Didnt manage to push through the drag, but it shocked me. Is this usual on emtbs? (thinking of getting trek rail 7)

It's the wide low pressure tires in 25kg full suspension mountainbike without assistance, not the motor.

 

[Zimmerframe]

This is interesting.

Most motors just cut at the limit (25kph in Europe for instance). It feels a bit like hitting a wall as you suddenly have this very heavy bike and all the rolling resistance to overcome on your own.

With the Gen4 at 25kph it doesn't just stop. The assistance drops off smoothly until a dribble at about 27.6 kph (seems to vary, I can't decide).

Then you're on your own, so you don't get the same "wall" feeling. I personally find the gen4 easy to pedal over the limit, even with Magic Mary's. Certainly easier than any other bike I've had.

I wonder for those of you state side, who have a cut out of 20mph if the "dribble zone" algorithm doesn't take into account the extra power needed because of the higher speed you'll be travelling, and therefore higher drag. So for us, it dribbles then you feel the motor disconnect and the whole thing feels like a nice smooth handover. For you, the motor's staying connected to "dribble" , but not giving enough to overcome the extra drag of the bike, so it feels like it's actually harder to pedal than it is until you hit 22mph and the motor completely disconnects.

You probably need to develop a technique where you accelerate upto 20-22 and push through to make it easier ?

 

[Gyre]

This is interesting.

Most motors just cut at the limit (25kph in Europe for instance). It feels a bit like hitting a wall as you suddenly have this very heavy bike and all the rolling resistance to overcome on your own.

With the Gen4 at 25kph it doesn't just stop. The assistance drops off smoothly until a dribble at about 27.6 kph (seems to vary, I can't decide).

Then you're on your own, so you don't get the same "wall" feeling. I personally find the gen4 easy to pedal over the limit, even with Magic Mary's. Certainly easier than any other bike I've had.

I wonder for those of you state side, who have a cut out of 20mph if the "dribble zone" algorithm doesn't take into account the extra power needed because of the higher speed you'll be travelling, and therefore higher drag. So for us, it dribbles then you feel the motor disconnect and the whole thing feels like a nice smooth handover. For you, the motor's staying connected to "dribble" , but not giving enough to overcome the extra drag of the bike, so it feels like it's actually harder to pedal than it is until you hit 22mph and the motor completely disconnects.

You probably need to develop a technique where you accelerate upto 20-22 and push through to make it easier ?

I don't have a very good frame of reference since I just know my Wild at the limiter and can't compare it to anything else.

That said, I'm really surprised to hear that you're experiencing any assistance at all over 25kph. My Wild cuts out a little prematurely. I'd put it at just over 19mph, sometimes I felt it cut out while the cyclecomputer is still reporting as low as somewhere in the 18's. To me, it feels abrupt but that could be the lack of reference. I always had the impression that Bosch is being conservative and cutting out completely with a bit of margin before 20mph.

Next chance I get I'll make a deliberate effort to pedal through from 19-23mph or thereabouts and see if I can feel anything change around 22. I haven't sensed anything like that this far, but I haven't made a concerted effort to look.

 

[TheRealPoMo]

This is interesting.

With the Gen4 at 25kph it doesn't just stop. The assistance drops off smoothly until a dribble at about 27.6 kph (seems to vary, I can't decide).

You sure about that? I would have thought a 25kph assistance limit is a limit, government regulations being what they are. It would explain the perception that Gen 4's are better at cutoff than Gen 2's tho.
In that case, no reason Bosch can't supply a Gen 2 update to do the same.
... except of course they want us to buy new bikes....

 

[Zimmerframe]

That said, I'm really surprised to hear that you're experiencing any assistance at all over 25kph.

Yes. It's definitely there, not much, but you can feel it . It's not really 25kph though. It's Purion 25kph. On GPS it's about 23kph, so it fully cuts out in real world speeds at about 25kph.

 

[Zimmerframe]

You sure about that?

100%. I guess they could argue it's not assisting anymore at that point, it's just countering it's own resistance ? Part of me thinks you can actually hear the physical disconnect when it does fully stop assisting. You can certainly here the actual motor spinning when it is assisting, whilst it's quiet, it's noticable compared to the older quieter Brose 1.3. So the "physical disconnect" I hear could be just the sound of that stopping. Will try it later and pay a bit more attention to sounds and maybe try to video it.

I think we've seen with all the motor/bike manufactures there's very little time or effort given to legacy support. You can't imagine them investing time in software development on an old motor platform - even Bosch who seem better than most.

 

[Hamina]

Just take the chain off, turn the motor and feel that the resistance is very small.

 

[Mteam]

There's virtually no drag from the motor itself when over the limit (or switched off), what you're feeling is the real effort required to pedal a 25kg full sus mountain bike with nobbly tyres.

As mentioned above, put the bike in a stand, take the chain off and turn the pedals by hand with the motor off, there is virtually no drag added by the motor.

 

[RickBullotta]

It's just as much an illusion of drag when 250W of assist is instantly removed!

 

[leix_toffee]

I have felt the same experience but as above I have put it down to 250w removed from a very heavy bike with extra wide nobbly tires and pretty much accepted it is what it is

 

[Gyre]

As mentioned above, put the bike in a stand, take the chain off and turn the pedals by hand with the motor off, there is virtually no drag added by the motor.

Well, that would back up my reluctance about using DHF/DHR2's on my acoustic bikes!

 

[Hamina]

I've just put 2,2bar (31,9083023 pounds per square inch for you 18th century folks) in my Minion DHR/DHF combo and thats enough to make the transition very very smooth at 25kmh limit. This is only for gravel like touring trips.

 

[Gyre]

I rode a few times to 23+ mph (Kiox speed) on today's ride with different times and places riding in a single gear looking to see if there's a change in pedaling drag around 22mph. In short, there wasn't anything that I wouldn't chalk up to running a higher cadence at higher speeds (and thus doing more work) as speed picked up. OFF mode didn't cause any noticeable change in resistance.

If there's something material going on with the drivetrain, it's either a one-off or below my sensitivity threshold.

 

[The EMF]

For what it’s worth my Whyte E-150 RS is a great bike to pedal. Yes when the motor assistance is turned off and the gradient increases the bike does feel heavier but I’ve never experienced any form of drag from the motor when pedalling above 20mph. I know this situation doesn’t happen too often (pedalling above 20 mph ) but often enough for me to notice any change in motor characteristics. I’ve had this bike over a year now and it still amazes me how capable this bike is.

 

[LowStandards]

I went out last night and I get a hard cut at 15.9mph after which it feels like i'm peddling through soup until 22-23ish when it appears to pedal like a normal bike.

Both in emtb lite and emtb

 

[Hamina]

I went out last night and I get a hard cut at 15.9mph after which it feels like i'm peddling through soup until 22-23ish when it appears to pedal like a normal bike.

Both in emtb lite and emtb

That doesn't sound logical.

 

[LowStandards]

That doesn't sound logical.

It's how it was, I tested it several times.


Really hard work until 22-23mph


No idea why or the physics/mentality of it, but there you go

 

[1oldfart]

I am pretty sure serious manufacturers do not mess with the law. I am in Canada so our legal limit is 32km/h.
Let say full assist happens at 29km, at 30 we get 90%, at 31 we get 50% at 32 we get 0% from the assist.
Depending on tires size some readings might be a bit off but do not trust all numbers you see.
Just like all 2.6 do not mesure 2.6, not all 32km/h are the same.
Like 3-4 years ago some manufacturers were 100% assist at 31 than 0% at 32
today most simply transition from 100% to 0% of assist in a smoother way.