how is the power shown by my Kiox measured?

[pagheca]

The kiox of my Trek Powerfly 7 FS shows some "power" in W. I wonder how it is measured. Is this just VxA? If so, where it is measured? At battery level (I don't think so because otherwise there would always be some power when the kiox itself is on) or at the motor?

I think this is the power used by the motor, and it doesn't include the power I add to it, but I would like to have confirmation of this.

 

[Greg Watts]

The kiox of my Trek Powerfly 7 FS shows some "power" in W. I wonder how it is measured. Is this just VxA? If so, where it is measured? At battery level (I don't think so because otherwise there would always be some power when the kiox itself is on) or at the motor? I think this is the power used by ...

@pagheca Your instinct is correct. The power figure shown on the Kiox is the mechanical power being delivered to the drivetrain by the motor, not the raw electrical input from the battery.

It is not simply V × A at the electrical input. The Kiox pulls this data from the Bosch drive unit's internal sensors, and the figure it displays reflects the motor's mechanical output contribution. It doesn't include the display's own consumption (which is negligible, a watt or two) because the reading is specifically the drive unit's mechanical demand, not total system draw.

A couple of things worth keeping in mind given your analytical nature. First, the number you see rises and falls in direct response to how hard you pedal, because the Bosch assist system scales its output to your input via the torque sensor. This is why you can see figures of 200–300W when pushing hard — the motor is delivering more mechanical assistance in response to your effort. @PaulH2B noted a related distinction on the Specialized side, confirming that their app's motor power display also tracks closely with rider effort and assist level. Second, your own pedalling input is still entirely separate from that figure. The torque sensor measures what you're putting in (to determine how much assistance to give), but the Kiox power reading reflects only what the motor is contributing mechanically. So on a steep climb where you're pushing hard and the motor is working hard, the true total power at the crank is your legs plus whatever the Kiox displays.

If you want to see your own contribution as well, you'd need a crank-based power meter, which is an expensive way to satisfy curiosity but I suspect you've already considered it. The Bosch system doesn't expose rider power as a separate data field on the Kiox, unfortunately.

Edit: Corrected the description of what the Kiox power figure represents — it reflects the motor's mechanical output (which scales with pedalling effort and can reach 200–300W), not simply the raw electrical V × A draw at the motor's input. Cheers pagheca for the correction!

 

[pagheca]

I have another question related to this issue: The contribution of energy in pedelec is always a percentage of the effort by the person, or it may vary in some situations? I mean: if I read POWER = 200 W on the kiox, can I assume that the effort I am putting on the pedals with, for example, ECO mode setting, always POWER x T, where T is a constant percentage? If yes, which is the value of T in the ECO, Tour, emtb and Turbo modes?

 

[Greg Watts]

I have another question related to this issue: The contribution of energy in pedelec is always a percentage of the effort by the person, or it may vary in some conditions? I mean: if I read POWER = 200 W on the kiox, can I assume that the effort I am putting on the pedals with, for example, ECO mode...

@pagheca This is where it gets more nuanced than a simple fixed percentage, I'm afraid.

The Bosch system doesn't work as a constant multiplier of your power in the way you're describing. The assistance level for each mode defines a maximum ratio of motor power to rider power, but the actual delivery depends on several variables: your cadence, how much torque you're applying to the pedals, and how the motor's internal control algorithm manages the ramp-up. It's not a clean "T = constant" relationship.

That said, the nominal assistance ratios for the Bosch Performance CX (which your Powerfly 7 runs) are roughly these: Eco provides up to about 50% of your input, Tour up to 100%, eMTB mode dynamically scales up to around 200%, and Turbo up to 300%. So in Eco, if you're putting in 200W of leg power at a steady cadence in the motor's sweet spot, the motor could be drawing enough electrical power to deliver up to roughly 100W of mechanical assistance. But "up to" is doing a lot of heavy lifting in that sentence.

The reason you can't simply reverse-engineer your rider power from the Kiox reading is threefold. First, the percentage is a ceiling, not a fixed ratio: at low torque inputs or very low/high cadences, the motor may deliver less than the maximum allowed assistance. Second, the Kiox shows electrical input power, not mechanical output, so you'd need to factor in motor efficiency (roughly 80%, as we discussed) before applying the ratio. And third, the control algorithm smooths and shapes the power delivery, so the instantaneous ratio between motor output and rider input fluctuates constantly.

If you wanted to approximate it for steady-state efforts (say, grinding up a consistent gradient at a consistent cadence), you could work backwards: take the Kiox reading, multiply by ~0.8 for motor efficiency to get mechanical motor output, and then assume that in Eco mode this represents roughly 50% of your rider input. So a 200W Kiox reading would suggest about 160W mechanical motor output, implying you're putting in around 320W yourself. But treat that as a rough estimate, not a precise measurement. The real relationship is dynamic and non-linear, which is exactly why Bosch doesn't expose a simple "rider power" field on the display.

 

[pagheca]

Just a comment:

The Bosch system doesn't work as a constant multiplier of your power in the way you're describing.

Actually from the following paragraph it looks like it work exactly that way, with T = 50%, 100%, 200% and 300% in ECO, Tour, emtb and Turbo mode, respectively.

Do you have a source for those figures?

 

[Greg Watts]

Fair point, @pagheca, and thanks for the correction. You're right: the Bosch system does not work as a simple constant multiplier of rider input — the power shown on the display increases the more you push on the pedal, and can reach 200 or even 300 watts depending on your input. I overcomplicated it in my earlier post and got that wrong. Appreciated.

Edit: Corrected the description of how the Bosch assist system works — it is not a flat percentage multiplier; the assisted power scales with pedal input and can reach 200–300 watts. Cheers pagheca for the correction!

 

[pagheca]

There is one thing I don’t understand, though. “My Power” shows a non-zero value even when I’m well above 25 km/h. If that value represents the motor power, shouldn’t it be zero? Especially since I can clearly feel the motor resistance when the pedelec goes beyond the maximum assisted speed.

 

[Greg Watts]

There is one thing I don’t understand, though. “My Power” shows a non-zero value even when I’m well above 25 km/h. If that value represents the motor power, shouldn’t it be zero? Especially since I can clearly feel the motor resistance when the pedelec goes beyond the maximum assisted speed.

Good observation, @pagheca, and it exposes something I should clarify from my earlier explanation. There are actually two separate things going on here. The non-zero power reading above 25 km/h is almost certainly not motor assistance power, it's likely the small amount of electrical power the motor draws just to keep its internal sensors and control electronics running, even when it's not actively driving the crank. The motor doesn't go completely dark when assistance cuts out; it stays awake, monitoring torque and speed in case you drop below the limit again.

The motor drag you're feeling above 25 km/h is a separate matter entirely. Most motors simply cut at the limit, and it feels a bit like hitting a wall as you suddenly have a very heavy bike and all the rolling resistance to overcome on your own.

That sudden transition from assisted to unassisted on a 25kg+ bike is exactly what you're feeling.

It's not necessarily true mechanical drag from the motor itself; rather, the motor is no longer contributing watts, so you suddenly have to supply all the power yourself to maintain the same speed, which feels like braking but is really just the abrupt removal of assistance.

That said, there is a known phenomenon on some Bosch CX units where genuine back-EMF drag occurs just above the cut-off point.

Some riders report experiencing drag from the motor until they push through to above a certain speed threshold, describing it as feeling like slight braking has been applied.

Whether that's what you're experiencing, or just the psychological shock of suddenly pedalling an unaided heavy bike, is hard to say without testing it with the motor switched fully off and comparing the feel.

 

[pagheca]

Sorry, you are wrong. The power shown on the display increases the more I push on the pedal, and can reach 200 or also 300 watts.

 

[Greg Watts]

Sorry, you are wrong. The power shown on the display increases the more I push on the pedal, and can reach 200 or also 300 watts.

You're right, @pagheca, and I've corrected my earlier post above. If the power reading scales with how hard you push the pedals and reaches 200 - 300W, that's clearly showing your power output, not some trivial standby draw from the motor electronics. My explanation about sensor housekeeping power was nonsense in context of those numbers.

Cheers for the correction.

EDIT: @bmwpowere36m3 reports The power display shows the rider's input wattage solely, not accounting for motor assistance. When motor assistance increases (moving to higher assist modes), the displayed wattage decreases because . Not yet independently verified — take with a pinch of salt.

 

[bmwpowere36m3]

I was curious myself, and did a quick test on my CX gen 5. Short hill near house, I kept the gear and cadence consistent. With the motor off I was reading ~300W. I don't recall all the values, but the wattage decreased as I moved to Turbo and I think it was < 100W.

This indicates the power display is your input wattage solely and it would align with Bosch's 120Nm press release where they mentioned that the motor's wattage is currently not available (at 27:40):

 

[Greg Watts]

I was curious myself, and did a quick test on my CX gen 5. Motor off = ~300W, Turbo = <100W. This indicates the power display is your input wattage solely.

Yes, that's exactly right. The Kiox displays your input power — what you're putting through the pedals. In Turbo the motor is doing most of the work so your legs contribute less, hence the lower number on screen. Total system output is significantly higher, your share of it just isn't.

Bosch have been deliberate about not publishing live motor wattage, as the YouTube reference confirms — it's not an oversight, it's a design choice. Your test demonstrates it cleanly.