Pedalling a Bosch CX without any motor assist

E-Wheels

Well-Known Member
Hi EBR Forum,
I'm just wondering how the Bosch CX motor works without any pedal assist
If for some reason I have to pedal with zero motor assist (as you would a normal bike) with a small 17 tooth motor sprocket and say a larger 30 tooth rear cassette sprocket it appears to be an under drive ratio
Does this mean that I will have a very high cadence and will be pedalling like a hamster in a wheel with these ratios or is there some sort of increased ratio mechanism in the motor even when no battery power is available to the motor
Thanks in advance
 

Ravi Kempaiah

Well-Known Member
Hi EBR Forum,
I'm just wondering how the Bosch CX motor works without any pedal assist
If for some reason I have to pedal with zero motor assist (as you would a normal bike) with a small 17 tooth motor sprocket and say a larger 30 tooth rear cassette sprocket it appears to be an under drive ratio
Does this mean that I will have a very high cadence and will be pedalling like a hamster in a wheel with these ratios or is there some sort of increased ratio mechanism in the motor even when no battery power is available to the motor
Thanks in advance
If it's eMTB with sprocket equalizing system, then it's going to be tough.

I'm fairly fit but pedaling a Haibike Full Seven S Rx without any assist for 5 miles took fairly high amount of work compared to my Easy motion Jumper.

Yes, if you put it on 30t granny gear, you'll do ok but your speed will be something like 10mph.
It would lot more easier on a hardtail without SES.
Yamaha or Brose systems freewheel better than Bosch.
So, on a CX motor, using 18t, 30t combination you can certainly do 5-10 miles without assist.

When I see that I'm running out of charge, I use ECO and that really takes the weight off.
 

E-Wheels

Well-Known Member
If it's eMTB with sprocket equalizing system, then it's going to be tough.

I'm fairly fit but pedaling a Haibike Full Seven S Rx without any assist for 5 miles took fairly high amount of work compared to my Easy motion Jumper.

Yes, if you put it on 30t granny gear, you'll do ok but your speed will be something like 10mph.
It would lot more easier on a hardtail without SES.
Yamaha or Brose systems freewheel better than Bosch.
So, on a CX motor, using 18t, 30t combination you can certainly do 5-10 miles without assist.

When I see that I'm running out of charge, I use ECO and that really takes the weight off.
Ravi,
Thanks for your prompt reply
I did read somewhere that the Brose and Yamaha systems would be more like riding a normal bike without motor assist due to the bigger chain wheels giving the over dive ratio
I couldn't find anything about the Bosch system but thought that as the Bosch sprocket spins approx 2x the pedal cadence with power assist that it might compensate some how by increasing the ratio in the drive mechanism by the same factor without power assist
What ever drive system I decide on it will be limited to 25km/hr max pedal assist in Australia
As I manage an average of 32km/hr on my non assist road bike for most of my commute I wanted an ebike drive that I can still pedal like a normal bike but have the motor assist kick in when I hit a hill or travel against a strong wind when my speed drops below 25km/hr
Looks like I will have to go with a drive system like Brose, Yamaha or Shimano with the bigger chain wheel to complement my style of riding
 

Ravi Kempaiah

Well-Known Member
Ravi,
Thanks for your prompt reply
I did read somewhere that the Brose and Yamaha systems would be more like riding a normal bike without motor assist due to the bigger chain wheels giving the over dive ratio
I couldn't find anything about the Bosch system but thought that as the Bosch sprocket spins approx 2x the pedal cadence with power assist that it might compensate some how by increasing the ratio in the drive mechanism by the same factor without power assist
What ever drive system I decide on it will be limited to 25km/hr max pedal assist in Australia
As I manage an average of 32km/hr on my non assist road bike for most of my commute I wanted an ebike drive that I can still pedal like a normal bike but have the motor assist kick in when I hit a hill or travel against a strong wind when my speed drops below 25km/hr
Looks like I will have to go with a drive system like Brose, Yamaha or Shimano with the bigger chain wheel to complement my style of riding
This is one area where Bosch design could be improved.
Most dealers aren't engineers or real riders, so they buy into many marketing blurbs.
Riding a Bosch CX or performance motor unassisted is Def more energy taxing than geared hub motors like BH EVO race.

Trying to maintain 25kph/17mph on a Bosch bike without assist, you'll be spinning a LOT. I think it's still doable if you have lighter bike like Urban S Rx.
 

TrevorB

Active Member
I regularly do 28-30km/hr (flat no wind) on my CX drive FS MTB running off road tyres. Assist cuts out at 25-27km. You shouldn't have any problems riding above cut off on touring bike with road tyres.
 

E-Wheels

Well-Known Member
I regularly do 28-30km/hr (flat no wind) on my CX drive FS MTB running off road tyres. Assist cuts out at 25-27km. You shouldn't have any problems riding above cut off on touring bike with road tyres.
TrevorB,
Thanks for the feed back
What gearing do you have on your bike to achieve these speeds and what is your cadence whilst doing 30km/hr
 

TrevorB

Active Member
11-42 cassette 15t chainring. The chainring spins x2.5 crank speed, so equivalent to 37.5t chainring. Given rider is going through x2.5 gearbox, losses maybe higher than likes of Shimano and Yamaha direct drive.

When it comes to pedalling unassisted the more important things are frame style (pedal efficiency) and tyres (rolling resistance). A hybrid on skinny tyres running 100psi is going to be faster than MTB on of road tyres.
 

E-Wheels

Well-Known Member
11-42 cassette 15t chainring. The chainring spins x2.5 crank speed, so equivalent to 37.5t chainring. Given rider is going through x2.5 gearbox, losses maybe higher than likes of Shimano and Yamaha direct drive.

When it comes to pedalling unassisted the more important things are frame style (pedal efficiency) and tyres (rolling resistance). A hybrid on skinny tyres running 100psi is going to be faster than MTB on of road tyres.
TrevorB,
Thanks for the reply
If I'm reading your post correctly you are saying the 15t motor drive sprocket continues to spin at x2.5 while pedalling, even after the motor has cut all assistance at the 25km/hr limit
I was lead to believe the crank sprocket would spin at x2.5 only while it received motor power and after the motor cut out it was x1 for every pedal rotation
 
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Robie

Active Member
Bulls Brose drive is very doable even with 2.8 plus tires on an FS full suspension mtb . Pretty enjoyable with no power because of their double chain rings upfront . And shifting is flawless , another plus is no banging gears when power is shut off.
 

E-Wheels

Well-Known Member
Bulls Brose drive is very doable even with 2.8 plus tires on an FS full suspension mtb . Pretty enjoyable with no power because of their double chain rings upfront . And shifting is flawless , another plus is no banging gears when power is shut off.
Robie,
The Bulls bikes look sweet
Unfortunately they are not available in Australia
The Brose system is of interest and I am looking into the Scott E-Silence 10 https://www.scott-sports.com/global/en/products/249761007/SCOTT-E-Silence-10-Bike as this reportedly will be available in Australia mid-late April
 

EddieJ

Well-Known Member
I've never found it an issue, and have even used the bike intentionally turned off completely when out on off road group rides with non ebike riders. I kind of use the extra weight of the bike as training aid, and also to shut up moaning regular mtb riders, especially when I get to top of a climb before them. I wouldn't want to do it daily though! :)

I should add that I run a 15 on the front, and an 11-42 on the rear
 

E-Wheels

Well-Known Member
I've never found it an issue, and have even used the bike intentionally turned off completely when out on off road group rides with non ebike riders. I kind of use the extra weight of the bike as training aid, and also to shut up moaning regular mtb riders, especially when I get to top of a climb before them. I wouldn't want to do it daily though! :)

I should add that I run a 15 on the front, and an 11-42 on the rear
EddieJ,
Thanks for your post re your experiences
Maybe you could give me a definitive yes or no as I'm still not sure of the responses to my query
Does the motor pinion spin at x2.5 when pedalling without any battery assistance or is it only a 1:1 ratio for the number of crank turns to motor pinion turns
 

EddieJ

Well-Known Member
I can confirm that even with the assist level turned off, that for every one pedal stroke, the sprocket turns 2.5 times. :)

In my case running a 15t front sprocket, that equates to a standard 37.5 front sprocket size.
 

E-Wheels

Well-Known Member
I can confirm that even with the assist level turned off, that for every one pedal stroke, the sprocket turns 2.5 times. :)

In my case running a 15t front sprocket, that equates to a standard 37.5 front sprocket size.
Thanks for the confirmation EddieJ
Very much appreciated