yamaha pw-x assist in a steep climb

[bikero]

Hi guys!

I'm starting to notice an interesting fact about the Yamaha PW-X motor (I have a haibike fullnine 8.0 2019).
Let's say I start a steep climb so I'm in my second lowest gear in the back, small chainring in the front.
I switch from what I typically use all the time, eco, to std. At some point I start to feel it's difficult for my feet
so I switch to high or even expw.

The problem that I find is that in such situations. even if I switch to high or expw, I don't feel any extra assistance.
To test it, in such a situation, I went to expw, continued to pedal and then went back to std. I didn't feel any decrease
of assistance when going back to std. It's like std was my only assistance level.

Of course, high and expw modes do actually work but on more moderate climbs and on higher gears. However, I cannot
use higher gears on a steep climb as I'm not able to maintain a decen cadence this way.

Is this why riders prefers the Bosch CX, to get a consistent rate of assistance even on steep climbs?

My main expectation is that when I increase the assist level I gradually relieve the difficulty in pedalling but it seems this
doesn't apply on steep climbs with the PW-X.

 

[Deleted member 4210]

Bosch is not better on climbs. What you are experiencing is you are expecting the wrong thing from increasing level of assist. It's more for adding assist at higher speeds, than for adding power, especially on a hill. On climbing hills, You want to downshift as much as you would a regular bike, because that higher motor (pedal rotations) speed is needed to maintain a higher torque level. (That gives you the 'power' to climb the hill).

Use your bike's gears for leverage, and it'll be better for not only good torque, but longer range, and increase the longevity of your motor. If you force the motor to work to hard, while having too low of cadence, you'll increase amp draw, draining the battery faster, likely reach the amp limit of the controller quicker and possibly cause the motor and the controller to overheat.

So the gears are important for both you and the motor, particularly on a mid drive.

You'll never get to the right cadence in a higher gear on a hill, unless you too, are really strong like Tour De France riders.

 

[GregGritton]

Bosch is not better on climbs. What you are experiencing is you are expecting the wrong thing from increasing level of assist. It's more for adding assist at higher speeds, than for adding power, especially on a hill. On climbing hills, You want to downshift as much as you would a regular bike, because that higher motor (pedal rotations) speed is needed to maintain a higher torque level. (That gives you the 'power' to climb the hill).

The OP indicated that he had downshifted to the 2nd lowest gear on the rear chainring, and the smallest (lowest) gear on the front chainring. So I don't think downshifting too little is the issue. On the contrary, it may be downshifting too much. Yamaha drives really don't like high cadence. see https://electricbikereview.com/foru...rison-chart-bosch-yamaha-shimano-brose.14085/. Note that the data posted there is from an older Yamaha system and Yamaha has reported accepting a higher cadence since them. Yamaha spec'ed the older motors to only 100RPM, while the CX-W is speced to 110 maximum RPM, 120RPM in EXPW mode, according to Yamaha's web site.

 

[GregGritton]

The other possibility is simply that the OP reached the maximum torque/power level for the motor. If the graph near the bottom of (Link Removed - No Longer Exists) is accurate, the Yahama motor has the same maximum output torque in ECO, STD, and HIGH modes. It just takes less input torque to reach the same output torque in the higher assist levels. In that case, switching to a Bosch motor might not help much.