Cadence range ?

[Link]

Is there a 'optimal' cadence for the Bosch motor ?, The only data I can find mentions that it supports cadence up to 120 rpm, but no minimum or ideal cadence. Whereas other motors seem to have a target cadence range. Maybe the Bosch doesn't have a target cadence limitation ?. That's a big selling point if true.

 

[1oldfart]

If you enjoy low cadence the best is Giant/Yamaha.

 

[Hamina]

The maximun power 600w is at 60rpm. On GEN2 and TURBO mode the torque starts descending after 70rpm.

 

[Link]

The maximun power 600w is at 60rpm. On GEN2 and TURBO mode the torque starts descending after 70rpm.

Not sure what you are saying there, anything above 70rpm cadence has a reduced torque delivery ?. That doesn't sound quite right

 

[Gyre]

Is there a 'optimal' cadence for the Bosch motor ?, The only data I can find mentions that it supports cadence up to 120 rpm, but no minimum or ideal cadence. Whereas other motors seem to have a target cadence range. Maybe the Bosch doesn't have a target cadence limitation ?. That's a big selling point if true.

On my CX Gen 4, I've never felt the motor fall off a peak no matter how fast I spin. Generally speaking, it feels very linear - put more torque and watts in, get more torque and watts out.

Edit: I do spend more than 95% of my time in Eco and Tour modes. In Turbo it does feel like the in/out ratio tends to be super strong down low and doesn't pick up at the same rate at higher speeds. Just my subjective opinion. I mostly use Turbo to haul my exhausted self back home after a long day.

 

[Hamina]

Not sure what you are saying there, anything above 70rpm cadence has a reduced torque delivery ?. That doesn't sound quite right

 

[Mikerb]

The Power/Cadence graph is more in line with my perception in riding my Whyte. Compared to my Levo I feel the Whyte needs a higher cadence to maintain a smooth power delivery......that is comparing Trail ( Levo) with EMTB ( Whyte). I dont know exactly but I would guess 70 rpm plus for the Whyte compared to 50rpm plus for the Levo.

Not sure that is the same in Turbo mode in both bikes though. The Levo seems to need a high cadence for best power delivery in Turbo whereas the Whyte in Turbo seems very powerful ...even brutish!.....from set off!.

 

[Link]

Interesting, so that's just for turbo mode...., like the other poster I don't use turbo, mainly eco, tour and sometimes emtb. I wonder what the graph looks like for the other modes.
Those graphs would indicate that there is a single cadence to get max power, anything below or above that it will drop away.

Obviously torque is what we are interested in, and that drops off after 80 according to this data. I would have expected Bosch to be highlighting this in their literature if it's important to keep below 80.
Is this a Bosch document ?, I had no luck finding anything official, not even a reference to cadence, apart from something about the cx works across a huge range of cadence. ?

 

[Gyre]

Keep in mind that the graph appears to be for Gen 2, not Gen 4.

 

[1oldfart]

The idea is to deliver the assistance when it is needed.
We start with a limited amount in the battery so delivering it when most needed is the key.
Otherwise it is constant drain, we need heavy bikes to carry a ton of energy.
Do you want 60 minutes of motorcycle feeling?
Do you want 3 hrs on a bike with some assist?

 

[Hamina]

There’s also torque sensor inside the motor to measure rider input.

Could be something like:
mode x rider torque x cadence = assistance.

Speedsensor provides feedback when to start ramp down assistance to keep assistance speed under 25kmh.

I think the motor has to also keep log somehow that it doesn’t violate the 250w max nonimal power.

 

[Darren]

Interesting, so that's just for turbo mode...., like the other poster I don't use turbo, mainly eco, tour and sometimes emtb. I wonder what the graph looks like for the other modes.
Those graphs would indicate that there is a single cadence to get max power, anything below or above that it will drop away.

Obviously torque is what we are interested in, and that drops off after 80 according to this data. I would have expected Bosch to be highlighting this in their literature if it's important to keep below 80.
Is this a Bosch document ?, I had no luck finding anything official, not even a reference to cadence, apart from something about the cx works across a huge range of cadence. ?

Looking at the red line on the graphs, 80 rpm is the point where both power and torque are both at maximum, indicating this is the most efficient rpm which would translate to max range.

 

[Gyre]

Ok, with a bit of hindsight (and at the risk of saying the obvious) it occurred to me that 90 NM torque at 80 RPM will put you just over 750 watts, which is the Class 1 limit in the US.

So anybody making a compliant eMTB is going to have to impose a lower and lower cadence taper point at their maximum assist level if they want to satisfy marketing with the highest torque figures. A bike with a hypothetical 100 NM motor would have to taper no later than 71 RPM in Turbo mode, and probably significantly sooner in order to offer some margin for error. That’s quite low.

Something to think about if a future round of bikes claims higher torque numbers.

Looking at the red line on the graphs, 80 rpm is the point where both power and torque are both at maximum, indicating this is the most efficient rpm which would translate to max range.

80rpm on Turbo assist would maximize the assist power and discharge rate. It would be close to the opposite of max range.

 

[L666GTB]

Spoke to the LBS.

They chatted with the Bosch rep a while back, saying that 90-100rpm cadence seems too be a good range for getting the most mileage from the battery.

 

[mak]

Without going into specifications its actually really obvious on the bosch where the ideal cadence is with just feel alone, providing the correct gear is selected.
The gen 4 does pull lower down the range since last years 85nm update was released but it has its lower limitations in the low 70 mark.
85 -90 feels optimised to me on a good climb in any mode although with turbo it feels like I'm putting no effort in at all

 

[JZA]

Ok, with a bit of hindsight (and at the risk of saying the obvious) it occurred to me that 90 NM torque at 80 RPM will put you just over 750 watts, which is the Class 1 limit in the US.

So anybody making a compliant eMTB is going to have to impose a lower and lower cadence taper point at their maximum assist level if they want to satisfy marketing with the highest torque figures. A bike with a hypothetical 100 NM motor would have to taper no later than 71 RPM in Turbo mode, and probably significantly sooner in order to offer some margin for error. That’s quite low.

Something to think about if a future round of bikes claims higher torque numbers.

80rpm on Turbo assist would maximize the assist power and discharge rate. It would be close to the opposite of max range.

I just thought I’d jump in here and give you some background into power and torque and how they are related. Power, in Watts, is equal to torque, in Newton Meters, times RPM I.e. cadence times a scaling factor for the units which in this case is 0.105 so Power=0.105*torque*RPM. You can flip that around to calculate torque so Torque=Power/(0.105*RPM). Let’s use the Bosch motor for example which we know can output a peak power of 600 Watts. So if we want to know what torque the motor is outputting at 90 RPM we can put those numbers in and get Torque=600/(0.105*90)=63.5 Nm.
My point is that motors don’t need to output maximum torque in order to reach maximum power output. Power and torque are two different things. Picture a tractor with a diesel engine that can produce 600 Nm of torque but can only rev slowly because it’s a big, heavy diesel engine with heavy pistons and a long throw I.e high piston speed for a given RPM. It has torque to pull/push things around but it can’t go fast. Now picture a sports car with the same 600 Nm of torque but it has a sporty, lightweight engine that can rev freely to high rpm. That engine is capable of producing far more power even though it has the same torque and in fact as the engine speed rises, it’ll start to produce less torque but still more power because it is gaining RPM while losing Nm at a slower rate. So even if an ebike motor is rated to 85Nm or 100Nm or whatever, this is only important for low RPM manoeuvring and once cadence/RPM increases, torque will decrease but power output will continue to increase. Ebike motor torque starts to taper off quite early. On the EP8 systems it has a little graph/line at the bottom of the screen that indicates the torque and you can see it only reaches 85Nm at very low cadence and most of the time it’s actually running around 75Nm and tapers even lower as cadence climbs. A high torque number is still useful when tractoring up a climb or taking off on a steep hill and it doesn’t matter if that torque output is lower at higher RPM because it’ll still produce more power which is more important for doing work I.e lifting an 80kg body up a hill or accelerating that body from a standstill up to 20km/h. But yeah as you mentioned, there is a legal limit on power output so that should be considered. The new Rocky Mountain e-bikes have 108Nm and apparently have a peak output of 880 watts so I’m not sure how that is legal but It’s pretty cool haha.

 

[Gyre]

I just thought I’d jump in here and give you some background into power and torque and how they are related.

Thanks. I have a pretty good idea of how power and torque are related. What I was trying to express (but perhaps the message was getting lost in the details) is that Bosch rewards as much cadence as possible in some modes but not in others. You kind of need to get to know each mode on its own terms and not just assume you're getting more of the same.