Riding an mid-drive ebike without battery...bafang BBS02 vs new stuff...

[unclejemima]

So my ebike is my summer mode of transportation to and fro. I love it. 1997 GT Bravado Cromo with BBS02.

Interestingly when my brother comes along for a ride, he has the identical bike (1997 GT Bravado Cromo) but his is sans battery...and to make things fair, I shut off my electricity. But my bro can right kick my bum when I shut my battery off.

Thing is, except for the extra weight...I'm thinking there is some huge drivetrain loss with the mid-drive if using it without electric power???
To make things worse, I'm running a Nuvinci 360 rear hub which is also not as efficient as a standard cogged derailer setup. But not sure how much of a difference this really makes?

Where my long story goes to is, are the newer high-end mountain bikes with the build-in (say bosch) mid-drive...do they have considerably less drivetrain loss than mine old school BBS02? Like if I were to get one of those, without the power on I'd at least be as efficient minus the extra weight? Or does having a mid-drive mean that drivetrain loss is just going to be par for the course???

Thanks for the input!

 

[Bigwheel]

All mid drives have a certain amount of parasitic drag due to the necessary gear reduction to them even the say the Bosch types. But you are also dealing with the extra weight of the motor, even sans battery, and that Nuvinci isn't that efficient either. Just use you lowest assist level and he can draft you and you both will have fun.

 

[docw009]

Here's my observation. If you take the chain off a regular BB, and give the pedals a twirl, they might spin for up to a minute,, and my 2016 BBS02B pedals will spin for 2-3 revolutions so I thought that meant the friction was low.

In the past six months, I've installed two more midrives. WIth the chain off test, the TSDZ2 will move 7/8 of a revolution. A newer BBS02B barely turns 1/2 revolution. Maybe they will loosen up. I am sure they steal a few watts.

In the meantime, I believe that it may be the friction under a heavy load that matters, My hub motor bike has close to 6000 miles and I let the cone/cup bearings in the BB go dry. Even dry, the pedals spun like a top with the above but they clattered. Greasing the bearings didn't seem to help. I felt groaning from the drivetrain when I pedalled harder. I upgraded the old bearings to a cartridge.

Greased the chain and the difference was incredible. Climbing the same hills on my daily run with less effort and no need to cheat and use throttle at the crest, Don't know if it was the chain or the BB, but it sure is better,
.

 

[2old]

I blinged out a GT Zaskar (Ritchey carbon fork, light wheels, etc) with a BBS02 into a 35 pound bike and rode it off road frequently with the motor off. The extra weight was felt, but the drivetrain seemed smooth and the bike pedaled well. As already stated, the only way to measure the loss would be to test similar systems with and without drivetrain "drag".

 

[tomjasz]

With Bosch, you give up the right to repair. Just use your bike on the lowest assist.

 

[unclejemima]

Perhaps it's my Nuvinci then?

I can drive my brothers identical GT Bravdo without motor/battery and it's like day and night. When I'm pedaling mine without the power on, it's pulling a sack of potatoes behind my bike compared to.

I'd be curious to try a high-end bike with a bosch mid-drive just for curiosity.

 

[amberwolf]

A NuVinci hub has a pretty big efficiency hit vs a plain direct chain drive, at least several times the power loss, IIRC. So depending on what drivetrain your brother's bike has, the difference could be easily noticeable.

Plain direct chain drive is about 2%, IIRC; I don't recall for sure the NV results I'd seen around here, but a quick google gives results as bad as 1/5 of the total power lost into the hub; this page

Which Bicycle Gearbox Has The Highest Drive Efficiency? Rohloff, Pinion, Shimano - CYCLINGABOUT

How do gearbox systems compare in terms of drivetrain efficiency? And what is the difference in cycling speed between gearbox options?

www.cyclingabout.com

shows some testing, and summarizes them giving the NV 85% efficiency, 15% loss. It also gives a derailer-shifted drive up to 10% loss. Both results depend on the actual ratios used, and the NV will depend on the torque input to it (more torque in means more loss because of the way it works internally, as there is more slippage in the fluid).