hill climbing? 750W hub versus 250W mid drive

[Chargeride]

That only applies to mid drives that can utilise the low freewheel gears.
A normal hub motor being dragged down to low rpm will start turning battery power into heat.

You can of course spend a lot of money on fancy versions designed to operate like that.

There is a sweet spot incline for my hub motor that beats even powerful midrives, running 2000w my hub will destroy a standard road legal midrive, there are plenty of videos though of fit riders on legal MTBs tearing away from powerful 1000w bikes ,I watched a video of that Crusher eFatbike off-road against a legal mtb up a steep difficult off-road path, the legal bike tore away, a combination of fit, skilled rider, using the power and gears effectively.

 

[Rexlion]

, the legal bike tore away, a combination of fit, skilled rider, using the power and gears effectively.

Yeah, I lack the first two! I'm a mediocre sprinter, and incapable on the long haul!

 

[Jeremy McCreary]

Simple questions for anyone who really knows, please:

Q1: In a typical derailleur-based mid-drive, does the chainring turn at the same rate as the pedals, yes or no?

Q2: If no to Q1, does the chainring turn faster or slower than the pedals?

NOT asking about multi-speed MGUs, just typical mid-drive motors. Thanks!

 

[Chargeride]

I'm going for faster considering how small they usually are

 

[fooferdoggie]

Simple questions for anyone who really knows, please:

Q1: In a typical derailleur-based mid-drive, does the chainring turn at the same rate as the pedals, yes or no?

Q2: If no to Q1, does the chainring turn faster or slower than the pedals?

NOT asking about multi-speed MGUs, just typical mid-drive motors. Thanks!

only. the older bosch had the chainring spinning at 2.5 to 1 it runs faster. like mine has a 18t chainring so about a 46t chain ring in use.

 

[Jeremy McCreary]

only. the older bosch had the chainring spinning at 2.5 to 1 it runs faster. like mine has a 18t chainring so about a 46t chain ring in use.

Thanks! So how many of the cassette cogs in that setup were smaller larger than 46t? (For example, 2 of 10.)

 

[Stefan Mikes]

Q1: In a typical derailleur-based mid-drive, does the chainring turn at the same rate as the pedals, yes or no?

In a good modern mid-drive motor derailleur system the chainring rotates at exactly the same rate as the cranks.

The reason for such a design is to enable the rider seamlessly pedal the e-bike whenever and for whatever reason the electrical assist ceases to act (like, switching the assist OFF or exceeding the maximum assisted speed or turning the system completely off).

In the case of no assist, multiple internal clutches disengage the motor, so the crankset is being immediately connected to the chainring the shortest possible way.

That enables the rider to apply huge changes to the chainring and the cassette size. My Vado SL came with a 44T chainring and a 11-42T 10s cassette. Now, I have a 36T chainring and a 11-51T 11s cassette there for great climbing properties. I once swapped the 48T chainring of my big Vado for a 36T one for mountain vacation, and now am running the e-bike with a 44T chainwheel, as it is optimal for my needs where I live.

 

[fooferdoggie]

Thanks! So how many of the cassette cogs in that setup were smaller larger than 46t? (For example, 2 of 10.)

for me none. my cassettes are ether 11-34 or 11-42.

 

[m@Robertson]

Try some mid-drive motor different from Bafang on a good e-bike

Yeah a 250w Bafang sounds like a BBS01 (which looks exactly like a BBS02), which is usually a 36v motor. It could also be one of their new small commercial oem motors. Assessing the tech another way: Look at the kind of motor all of the quality name brand manufactured e-mtb's use.

Q1: In a typical derailleur-based mid-drive, does the chainring turn at the same rate as the pedals, yes or no?

On a BBSHD this can either be 'same' or 'faster', depending on the assist level AND the settings you plug in. If you are using the factory settings the answer will pretty much always be 'faster'. Set it up like I have mine and its pretty much always 'same rate'. Factory settings let the motor run away from the rider and pretty much totally account for all the bad reviews of that line's performance.

Q2: If no to Q1, does the chainring turn faster or slower than the pedals?

It will never be slower on a BBSHD. There's a clutch inside that won't let that happen.

 

[Jeremy McCreary]

Yeah a 250w Bafang sounds like a BBS01 (which looks exactly like a BBS02), which is usually a 36v motor. It could also be one of their new small commercial oem motors. Assessing the tech another way: Look at the kind of motor all of the quality name brand manufactured e-mtb's use.


On a BBSHD this can either be 'same' or 'faster', depending on the assist level AND the settings you plug in. If you are using the factory settings the answer will pretty much always be 'faster'. Set it up like I have mine and its pretty much always 'same rate'. Factory settings let the motor run away from the rider and pretty much totally account for all the bad reviews of that line's performance.

It will never be slower on a BBSHD. There's a clutch inside that won't let that happen.

Thanks! Maybe you can help me understand the oft-claimed mid-drive climbing advantage.

Look at enough official mid-drive+derailleur bike specs, and you'll see that most have chainrings larger than any of their stock cassette cogs. Torque-wise, this puts the mid-drive motor at a mechanical disadvantage in every gear. Also makes the both motor torque and mechanical power subject to drivetrain frictional losses.

Why is this better than applying the same motor torque and mechanical power directly to rear hub? What am I missing?

Thoughts on this, @mschwett ?

 

[fooferdoggie]

Thanks! Maybe you can help me understand the oft-claimed mid-drive climbing advantage.

Look at enough official mid-drive+derailleur bike specs, and you'll see that most have chainrings larger than any of their stock cassette cogs. Torque-wise, this puts the mid-drive motor at a mechanical disadvantage in every gear. Also makes the both motor torque and mechanical power subject to drivetrain frictional losses.

Why is this better than applying the same motor torque and mechanical power directly to rear hub? What am I missing?

Thoughts on this, @mschwett ?

if nothing else efficiency. if you keep up say a 80 rpm cadence while climbing them motor is going to be running close to its most science constantly. but most hubs dont have good gearing and it would be hard to compare them accurately. butI watched a video of a guy with a bike that was the same gearing using a bafang hub and mid drive both the same wattage climbing a hill and the mid drive blew the hub drive away. Hell putting 200 watts of human effort through the drivetrain will out climb a 200 watt hub motor any day.

 

[Jeremy McCreary]

if nothing else efficiency. if you keep up say a 80 rpm cadence while climbing them motor is going to be running close to its most science constantly. but most hubs dont have good gearing and it would be hard to compare them accurately. butI watched a video of a guy with a bike that was the same gearing using a bafang hub and mid drive both the same wattage climbing a hill and the mid drive blew the hub drive away. Hell putting 200 watts of human effort through the drivetrain will out climb a 200 watt hub motor any day.

Thanks! Wonder why gearing a hub motor down to wheel speed is any harder than a mid motor down to chainring speed? Maybe it's a room problem.

 

[fooferdoggie]

Thanks! Wonder why gearing a hub motor down to wheel speed is any harder than a mid motor down to chainring speed? Maybe it's a room problem.

but you have variable speed in the hub Motor. if you keep your rpms at 80 and shift on a mid drive them motor is going to be close to its peak all the time. its also why you see such long ranges on bosch and specialized with only 36v smaller batteries.

 

[Jeremy McCreary]

but you have variable speed in the hub Motor. if you keep your rpms at 80 and shift on a mid drive them motor is going to be close to its peak all the time. its also why you see such long ranges on bosch and specialized with only 36v smaller batteries.

Ah, that makes a lot of sense. I do everything I can to keep a cadence of 85±5 RPM just to keep my knees happy. Sounds like a mid-drive would be happy with that, too.

 

[Stefan Mikes]

you'll see that most have chainrings larger than any of their stock cassette cogs

Most e-MTBs and gravel e-bikes have their chainrings smaller then their big cassette gears for the pure virtue of amplifying the torque at the rear wheel.

What can you see here?

You see big chainrings and smaller cassettes on your typical commuter mid-drive e-bikes for high speed as the sacrifice for their climbing capability. Still a good mid-drive e-bike will offset the gearing with its high peak power.

Jeremy, try demo riding a mid-drive e-bike made of a named animal

(It looks @Jeremy McCreary has Ignored me).

 

[fooferdoggie]

Ah, that makes a lot of sense. I do everything I can to keep a cadence of 85±5 RPM just to keep my knees happy. Sounds like a mid-drive would be happy with that, too.

yep I tested the bosch at different rpms. and yo need 70rpms for them motor to give its all. like this 20% grade hill at 40 rpms I maxed the motor out putting out 450 watts myself. but with a smaller chainring I was able to spin at 80 rpms and put out 550 watts and I don't think I hit the motor limit. p-lus the faster you can peddle them ore torque you can generate for the same amount of effort. 450 watts at 40 rpm is far harder then at 80 rpms.

 

[Jeremy McCreary]

yep I tested the bosch at different rpms. and yo need 70rpms for them motor to give its all. like this 20% grade hill at 40 rpms I maxed the motor out putting out 450 watts myself. but with a smaller chainring I was able to spin at 80 rpms and put out 550 watts and I don't think I hit the motor limit. p-lus the faster you can peddle them ore torque you can generate for the same amount of effort. 450 watts at 40 rpm is far harder then at 80 rpms.

Seems odd, then, that most of the derailleur mid-drive specs I've seen have at most one low gear with a cog equal to or larger than the chainring. Most have none.

With that kind of gearing, how is an average rider on 26+ inch wheels supposed to keep up cadence to keep the mid motor in its happy place on big hills? Not the weakest cyclist but doubt that my legs ever put out 450W.

 

[Mr. Coffee]

Seems odd, then, that most of the derailleur mid-drive specs I've seen have at most one low gear with a cog equal to or larger than the chainring. Most have none.

Because most bikes sold are wildly geared too high for normal people. And electric bikes make this even worse.

I think most bike manufacturers think all of their riders have thighs and quads that are bigger than most tree trunks.

 

[Jeremy McCreary]

What's too high in gear inches?

My 500W hub-drive with 27.5 inch tires came with 9-speeds and 42t / 34-11t gearing. That came to a range of 34 - 105 gear inches — WAY too high for our many short 5-10% grades and no go on anything steeper.

Now it has 10-speeds with 40t / 42-11t gearing for a 26-100 gear-inch range — more than capable in this terrain with acceptable exertion. No problem keeping preferred cadence, and forward speed generally stays above 5 mph on hills. The geared hub motor seems happy with this arrangement.

 

[fooferdoggie]

Seems odd, then, that most of the derailleur mid-drive specs I've seen have at most one low gear with a cog equal to or larger than the chainring. Most have none.

With that kind of gearing, how is an average rider on 26+ inch wheels supposed to keep up cadence to keep the mid motor in its happy place on big hills? Not the weakest cyclist but doubt that my legs ever put out 450W.

thats the sacrifice you make with a mid drive only one chainring. so you need to dial it in for the type of riding you do. on our tandem we have a 36t chaining and we can climb anything with it. I climb about the same amount of effort on my trek with a 42t. chainring. but I could go smaller as I never go 28mph anymore. I usually put about 450 watts on a 20% grade. a couple ears ago I could do 700 watts for a few second starting off and popping a weelie. I did 550 watts testing the bosch motor going up a 20% grade to keep the rpms at 80. man my heart rate was like 200 on that two block stretch it was so hard for me.