Carrera CityCross assistance glitch

[user00856]

Odd one this, bear with me...

We have two of these Carerra CityCross ebikes; OH's is 2 years old and works fine, mine is 6 months old and doesn't. Both were bought second hand quite recently.

On OH's bike on full assist (mode 3) the motor propels it smoothly to about 15.5mph then drops out, as expected. Once the speed drops to about 14.9 it cuts in again and increases the speed smoothly back to 15.5 or so, exactly as expected and how you'd want it to work.

On mine it reaches 15.5 / 15.6 in the same smooth way, but then as the assist drops out the speed drops steadily all the way back to around 13.3 / 13.4 before the assist kicks back in. It actually takes quite a while for that drop to happen - pedalling is the obvious answer but there's a real sense of fighting against the motor to get the speed back up. If it's allowed to drop to 13.n the assist softly kicks in and pushes it back to 15.5 +/- in the usual way.

I've recreated this consistently (we have a closed road just round the corner) using the Garmin off my road bike and pedalling slowly in a low gear to keep the assist on, and it never changes - hit 15.n, drop steadily to 13.n then back to 15.n. It makes it almost unrideable with the speed dropping that slowly and therefore the assist MIA for that time. Compare and contrast with OH's bike which momentarily and unnoticeably loses assist at 15.5 / 6 before gracefully returning at just below 15mph

I've cleaned the sensor on the bottom bracket but tbh it's so consistent that it can't reasonably be that. My hunch is that it's a s/w glitch that fails to trigger the assist at the intended speed (14.9) and instead lets it fall all the way to 13.3 before kicking it back in.

Anyone else seen this? Any suggestions?

Thanks.

 

[Drago]

2 year warranty, take it to the shop.

 

[user00856]

Warranty not transferable so not an option.

 

[ebikeerwidnes]

I know that they changed the motor/battery/controller system a while ago
Check if the motors are of the same make - they may just be made to react in different ways

 

[gbb]

Are both bikes fitted with exactly the same system (mine has no assist, eco, tour, climb and sprint)
If I tootle along in eco, it doesnt propel me along at 15 mph, probably 13.
If I tootle along in tour, it does propel me along at around 15.

Also, are both bikes in the same gear ? If I tootle along in eco and its beginning to struggle (say on an incline) , change up a gear...and the motor kicks in harder.

If both those bikes have differing systems and gears, that may explain it.

 

[Drago]

They will have different set ups, as Carrera switched to the HESC+ torque sensing set up very late in 2019.

It still sounds like something might be awry though.

 

[user00856]

Are both bikes fitted with exactly the same system (mine has no assist, eco, tour, climb and sprint)
If I tootle along in eco, it doesnt propel me along at 15 mph, probably 13.
If I tootle along in tour, it does propel me along at around 15.

Also, are both bikes in the same gear ? If I tootle along in eco and its beginning to struggle (say on an incline) , change up a gear...and the motor kicks in harder.

If both those bikes have differing systems and gears, that may explain it.

The City Cross has a very simple implementation; in effect the rider selects the speed to ride at with the assistance either off or at 9, 12 or 15mph. There are no torque sensors to adjust the assistance depending on pedal input and as the motor is in the rear wheel hub the gears are outside of the equation for assistance.

The issue arises if we're going up a longish incline - the speed tops out at 15.5 then all assistance is lost until the speed drops to about 13.3, and in the meantime pedalling is harder as it feels like I'm trying to overcome the motor drag as well as pedal a 19Kg bike (+ me) up a hill. That pretty much defeats the point of having an ebike, esp as OH is busy disapearing into the distance at 14.9-15.5mph.

It still sounds like something might be awry though.

Indeed. Which is where we came in. I plan to go direct to the manufacturer, but was interested to see if this was a known issue that other Carerra Cross City ebike owners had encountered and whether there was already a fix out there.

 

[Drago]

Well, I can reassure you on that one - it's the first time I've heard of those symptoms.

 

[ebikeerwidnes]

Mine is pre the 2019 changes
but if it helps - I have 3 assist levels - in all levels the assist will continue up to about 15.5 mph - just at different amount of assist
so you have to pedal more to get to 15,5 in low assist than you do in high assist - but you still get there and I can still hear the motor helping

 

[user00856]

Hi E. Thanks for the response but I suspect yours has different running gear to our 2 models. On both of ours the assist tops out at the speed that maps to the selected assist setting, so either 9, 12 or 15mph. You're right that the motor continues to run above the lower thresholds but it's not adding anything other than providing a baseline of 9 or 12mph, and it cuts out at 15.5 (+/-) anyway. My experience is that pedalling harder to hit any speed higher than threshold is fighting not just the combined total weight of the bike rider & any payload, it's also figthing against the drag of the motor. As I said, it rather defeats the point of having an ebike, unless pootling along at 9-12mph is all the rider wants.

 

[Drago]

Thats deffo not right. When above the motors assistance range you shouldn't feel anymappreciable drag. I presume they feed just enough current to the motor to kind of idle it with little load, but whatever, it shouldn't be resisting you.

 

[ebikeerwidnes]

Thats deffo not right. When above the motors assistance range you shouldn't feel anymappreciable drag. I presume they feed just enough current to the motor to kind of idle it with little load, but whatever, it shouldn't be resisting you.

I concur with my learned fiend (sorry friend - probably)

this is based on the 4 ebikes I have owned - no drag seen above the cut off on any of them