Bosch Performance Motor vs. Brose, Shimano, Yamaha (Drag vs. Full Sized Chainring)

Court

Administrator
Staff member
Hi guys, I see comments about the "drag" that Bosch Performance Line motors produce compared to some competing hardware out there and I wanted to clarify with my understanding and invite you to share:

My understanding is that the only drag produced on Bosch Performance Line motors is the reduction gear in the bottom bracket. It won't slow you down from coasting faster but does produce a bit of friction while pedaling because the chainring has to spin 2.5x for each crank revolution. I think some people hear "drag" and think the bike won't coast just as efficiently or be able to pedal above 20 mph and that is not the case at all, even if the motor is turned off. My experience has been that the motor doesn't pedal quite as efficiently because of the 2.5x conversion and in my experience the resistance is minimal. The benefits however are mechanical advantage for efficiency of motor operation, improved chain retention, and possibly improved ground clearance. Does this sound accurate to you?

Again, I am spelling this out and inviting conversation because I think there is confusion and misinformation around why electric bikes can feel difficult to pedal beyond 20 mph (or 28 mph if it's a Class 3 speed pedelec) and my experience is that the combination of wind resistance and a feeling of "slowdown" as the motor fades out can create the illusion of "drag" but the only real drag happening is when you turn the crank arms and it converts each pedal stroke into a 2.5x chainring spin. Again, this is unique to the Bosch Performance Line motors but is not present on their new 2018 Active Line product. That motor tends to be more gentle and allows you to pedal backwards and actually move the chain (though there is some friction when doing so).

Competitors like Brose advertise that their motor has a built-in freewheel so that you can pedal faster than the motor or without the motor and nothing inside will be turned. That's a neat feature and is made possible by the full size chainring design. I'm not saying one is better than the other, just that the "drag" some people refer to might be exaggerated. I frequently surpass 20 mph while pedaling on flats and have even reached 40+ mph when coasting down hills on Bosch Performance Line motor powered electric bikes. What you do get from this company is durability according to the shops I visit who carry multiple brands, a universal and backwards compatible battery design (at least with the Powerpack models), and a great warranty with a dedicated service partner in the US.

Yes, I'm a bit of a Bosch fanboy because they were one of the first high-quality ebike brands to enter the USA, but I have also owned Brose powered electric bikes, hub motors, and other friction drive systems. Nobody paid me to write this guide, I simply wanted to share my experience and invite input :)

The photo below shows a unique design where the smaller chainring on a Bosch Performance Line motor is next to a full sized chainring on a tandem electric bike. I think it demonstrates the unique sizing differences and shows how the smaller chainring has to spin faster in order to move the chain the same distance as the full sized chainring, the internal gearing that makes this possible is what produces a bit of friction but your still have a big mechanical advantage against this friction because of the length of your crank arms (usually 170 mm in length). Many times the Bosch chainring is obscured by an alloy protector or plastic cover, so this photo lets you see a bit closer:

moustache-samedi-27-x2-chainrings-small-large-comparison.jpg
 

PaulGee

Member
I have very limited experience test riding the Bosch bikes but for the sake of discussion would like to share my non-expert experience. Having only tested two MTB Bosch CX mid drives on two separate occasions, one at the recent Bike Expo in Philly, I did find that both bikes seemed more difficult to pedal above the 2O mph limit compared to the Brose, Yamaha and Shimano bikes which I also have limited experience test riding. Court - after reading your comments, my experience could be more related to the abrupt cut off of power, due to the controller, than the actual gearing on the Bosch and the fact it gives you very peppy power up to about the 20 mph limit. The bikes I rode it seemed like the motor cut off in the 18 mph range while the other drive systems in general seemed to gradually power down and provide some assistance up to or maybe 1-2 mph beyond 20 mph. Other than that, I did enjoy the power characteristic of the Bosch CX drive.
 
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Over50

Well-Known Member
...I did find that both bikes seemed more difficult to pedal above the 2O mph limit compared to the Brose, Yamaha and Shimano bikes which I also have limited experience test riding ... The bikes I rode it seemed like the motor cut off in the 18 mph range ...

My experience with my Haibike XDuro Trekking 4.0 with the CX motor: it cuts off somewhere between 19.5 and 19.8 MPH consistently and it is so smooth I can't even really detect it except for the fact that I feel some increased resistance. There is no noise or jerking of the motor to indicate shutoff or restart. But if I want to increase my speed past 20 mph - it is really difficult. On flat ground, I can actually obtain higher speeds (with less effort after 20 mph) on my human powered Spot Champa (Alfine 8 speed). I can consistently max out around 23 mph on my human powered bike (without killing myself) whereas it takes a lot more effort to hit that on my Haibike. Of course the Spot is a lot lighter. In my commuting on the Haibike, I've concluded it is counter-productive to let the motor cutout with the intent to increase my speed - say to catch a green light. Counter-productive because the amount of energy I have to expend for that extra 1 or 2 mph really isn't worth it. I've really stopped trying to push the bike past 20 and have become accustomed to cruising around 18-19 and making my time with the jack-rabbit acceleration of the CX motor from the stops. Ultimately I'd level high praise at the CX motor for two things: 1). the smooth and powerful acceleration up to the cutoff and 2). the smooth, almost undetectable cutoff of the motor approaching 20 mph. The negative is pedaling the bike over 20 mph - really difficult to do on a flat.
 

Shoestring

Active Member
I may be in the minority, but the necessity to pedal above 20/28 mph as the case may be, is a non-issue for me. That defeats the whole purpose of assisted fun!!
 

rich c

Well-Known Member
I may be in the minority, but the necessity to pedal above 20/28 mph as the case may be, is a non-issue for me. That defeats the whole purpose of assisted fun!!

It's not a necessity for me to go over 20mph, it's just plain exhilarating! Riding a traditional bike at that kind of speed, with these old legs, was not a possibility. I agree with the comment about riding a Bosch system with the assist shut off. It sounds and feels unnatural for the mechanism.
 

Sweetwater

Active Member
I have a Bosch Performance Line Speed on my FullSeven S Pro.
I have ridden Yamaha and Brose bikes that cut out at 20 mph, mine provides boost to 28 mph.
I have a route that climbs 3000 ft from 5000 ft to 8000 ft over 11 miles.
Several times I have depleted the 400 Wh battery and climbed the final bit without assistance.
The bike does labor under that scenario, so do I, and it seems that there is some "drag" when that happens.
Otherwise, I have always descended without assist, often without the bike turned on.
I easily reach speeds approaching 35 mph or a bit more, held it to less than 40 mph for safety.
Under those conditions, I haven't felt any drag and the bike's final 2 gears take me well above 28 mph.
 

barry c

New Member
I have the 2017 Haibike Xduro all mt 7 and it does feel like there is more drag than the Brose. I rented a specialized levo with the brose and rode it against my bike and the levo ran out of battery sooner on the same ride with the same size battery. So how does that stack up on energy use? Are you really going to ride your bike with a flat battery. I think not. I purchased a second battery and have a 40+ maximum effort single track mile range.