Class 3 Road Bikes

[Alaskan]

Here is a 36 lb. carbon frame ebike with a Bosch speed motor, 500 watt battery and a 2x11 drive train (32/48 front - 11-34 cassette) and 700c rims

Cannondale Topstone Neo Carbon 2 Speed Electric Bike - 2021 | REI Co-op

Off-road capable and on-road comfortable, the Cannondale Topstone Neo Carbon 2 Speed e-bike is a gravel bike like no other, withpedal assist up to 28 mph and a range of up to 78 mi.

www.rei.com

 

[Oski1997]

These graphs are weird. I know the blog, but he does a poor job of explaining how the graphs should be read. He also talks about tuning the motor (rewinding with thicker wires).

What you need is a power vs cadence (or torque vs cadence which give the same information).

To supply 70nm at 72rpm motor output has to be outputting 530W continuously. That is way over the stated nominal 250W and most likely not sustainable for long periods.

Ok thanks

 

[Alaskan]

The gen 4 Bosch speed motor on my trek Allant+9.9s has a nominal 250w rating and can output up to 85nm of torque at a cadence of 70 rpm continually. I did a climb this summer that was a steady 5-7% grade for 12 miles with an elevation gain of 3,000 feet. It was almost 2 hours of climbing and went without a hiccup.

 

[Oski1997]

The gen 4 Bosch speed motor on my trek Allant+9.9s has a nominal 250w rating and can output up to 85nm of torque at a cadence of 70 rmp continually. I did a climb this summer that was a steady 5-7% grade for 12 miles with an elevation gain of 3,000 feet. It was almost 2 hours of climbing and went without a hiccup.
View attachment 82093
View attachment 82094

Wow, That is awesome!!

 

[Johnny]

The gen 4 Bosch speed motor on my trek Allant+9.9s has a nominal 250w rating and can output up to 85nm of torque at a cadence of 70 rmp continually. I did a climb this summer that was a steady 5-7% grade for 12 miles with an elevation gain of 3,000 feet. It was almost 2 hours of climbing and went without a hiccup.

First of all at 70 rpm according to Trek's own data the maximum is less than 80nm. But let's put that aside.

The question is how do you know that you got 85nm ?

Let's make a quick calculation of battery consumption for the claimed 12 mile-2hour climb:

To have 85nm at 70rpm, motor has to output around 620W!. At that power level, with all the losses, the efficiency should be at best in the low 70's. But let's instead say %80. That means that your average power consumption is at least 620/0.8=775W during that climb!

In just that two hours of climb, that translates into 775x2=1550WH! That is only the 12 mile climb section.
I see that you have a total of 500+625=1125wh battery, where is the rest of that energy coming from?
In short, it is impossible to get anywhere close to that rpm/torque value continuously as claimed.

Also according to Bosch's own estimate the average motor output was around 187W (rider averaged 88W and it was %32 percent of the total output hence the computation follows) taking all the losses into account, the total consumption would be around 800-850wh during that 3.5 hours ride, if the Bosch's reported number is right.

This is why they separate nominal and peak numbers in the specs. One should think carefully before repeating marketing numbers...

Moreover,
The mechanical power output also does not add up.

Climbing 12 miles at %7 percent grade(assuming the worst) in two hours, that is an average speed of 6mph, for a total 270lbs rider + bike requires an average power around 265W!!! (given no wind). If as claimed one was getting 85nm at 70rpm hence 620W constantly, even without any effort on the rider's part, rider should be able to climb this hill at least at 13mph! hence less than an hour...

 

[Scarlet/Fire]

The Cannondale Topstone Neo Carbon series all have a gen 4 Bosch speed motor. The latest firmware update on that motor boosts the max torque to 85 Nm and a 500 watt power tube. I ride a Topstone Neo Carbon 3 which is the same bike, more gravel oriented with a lefty suspension fork, 650b rims, weighs 39 lbs. and a 1x11 drive train. The Neo Carbon 2 with its fixed fork, 700a rims and 2x11 drive train is a bit more of a road bike and weighs 36 lbs.

The turbo creo has way less torque but with the internal 320 watt battery plus the160 watt battery boost that mounts sits in the bottle cage at the bottom of the seat tube, the total battery wattage is 480. Also note the turbo creo is a full 8-15 pounds lighter than any of the others at 28 lbs. Clearly a bike oriented towards a fitter rider and not the hill eater that the Bosch powered bikes are, but it likely has the greatest range.

I’m curious about the torque numbers - if you have 70 on a hub and 70 on a mid drive how would they describe the difference with the mechanical advantage of the gears? I hear anecdotes like this mid drive climbs like a mountain goat - but don’t know of a numerical way to compare the two ? Sorry just a rambling thought/ cheers

 

[WattsUpDude]

I’m curious about the torque numbers - if you have 70 on a hub and 70 on a mid drive how would they describe the difference with the mechanical advantage of the gears? I hear anecdotes like this mid drive climbs like a mountain goat - but don’t know of a numerical way to compare the two ? Sorry just a rambling thought/ cheers

I think the simplest way to think about it is to imagine you’re trying to loosen a stuck bolt. If you’re using a short wrench (hub drive) it’s much tougher to loosen than if you’re using a long breaker bar (middrive + gearing) even if you’re putting the same weight on both tools.

 

[Johnny]

I’m curious about the torque numbers - if you have 70 on a hub and 70 on a mid drive how would they describe the difference with the mechanical advantage of the gears? I hear anecdotes like this mid drive climbs like a mountain goat - but don’t know of a numerical way to compare the two ? Sorry just a rambling thought/ cheers

The numerical calculation is quite simple. If we assume no drivetrain losses:

Torque at the Crank x (Number of teeth on the cog)/(number of teeth on the Chainring) = Torque at the hub.

Example, suppose you have a 42T chainring.

Assuming mid drive is giving 70 nm torque at the crank:
If you are at 11T cog on the cassette -> 70 x 11/42 = 18.3nm at the hub.
If you are at 46T cog on the cassette -> 70x46/42 = 76.6nm at the hub.

If you want to incorporate drivetrain efficiency, multiply the numbers with the assumed efficiency.