hill climbing? 750W hub versus 250W mid drive

Rexlion

Well-Known Member
Region
USA
City
Tulsa metro
For those who have ridden up hills on both a hub and a mid drive, how do they compare in terms of how easy and quick they are to make it up the hill? I have a 750W geared rear hub with (IIRC) 90 Nm torque, and torque sensor at the crank. Thinking of getting a Bosch mid drive with 250W, 65 Nm torque. Assuming the same gear inches for the gearing (and let's suppose we use the peak PAS since it's a really steep hill), which one will pedal easier up the hill? TIA. Mainly I just want to make sure I don't buy the mid drive and then regret it, which I would do if it made life harder on the inclines.

I enjoy bicycling, but if I wanted to work my tail off during the climbs 😝 I'd just ride an acoustic!
 
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You'll need some lower gears in a hub drive for the steeper hills. My hub motor bike has 24 gears, my 750w mid-drive has 8. Their riding performance is similar. The 500w hub motor I have pulls up to 1400w, so that power sure helps on steep hills.
 
Thanks to you all for your input. Hearing that the mid drive will actually peak much higher than 250W is very reassuring. I have seen posts where people said mid drives are better, but looking at the torque numbers made me doubt that a mid drive with lower torque rating could climb easier than a (torque-sensing) hub with a higher torque rating (all other factors being equal). That's why I wanted to hear people's experiences.
 
You'll need some lower gears in a hub drive for the steeper hills. My hub motor bike has 24 gears, my 750w mid-drive has 8. Their riding performance is similar. The 500w hub motor I have pulls up to 1400w, so that power sure helps on steep hills.
Good point. My current Ride1Up LMTD soars with power, but unpowered it's a real dog on the least uphill incline; my analog Trek bike does better.
 
with a mid drive you will have to put effort into it. but my bosch took over 550 wats of me working to hit is peak. in short bursts it was over 700 watts.
Now that's an interesting comment. I have some hills near my house that will bog me down in 1st gear on my 21-speed Trek analog bike and will wear my legs down to a nub even at that. Those hills are so unpleasant on the Trek, I'd simply stopped riding there. But once I got my Ride1Up LMTD I can do those hills on PAS 1 in 3rd gear (of 8), PAS 2 in 5th or 6th, both with reasonable but not uncomfortable effort, or I can take them in top PAS 3 in high gear (20+ mph) with the same effort. I usually use PAS 1 or 2 depending on how tired I am getting. I think these hills are about 5% grade. But my point is, I have that much reserve power with the current ebike. If I still could pedal the hills on the mid drive ebike with top assist at 20 mph, then I'd know I am not giving anything up (again, not that I would go that fast, but it's nice to have some power in reserve in case I am someday pedaling an even steeper grade... like, if I went up Cadillac Mountain in Acadia NP, which has a "steepest quarter mile" of 7.4% and a little bit of the climb is in the 10%-15% range.
 
Now that's an interesting comment. I have some hills near my house that will bog me down in 1st gear on my 21-speed Trek analog bike and will wear my legs down to a nub even at that. Those hills are so unpleasant on the Trek, I'd simply stopped riding there. But once I got my Ride1Up LMTD I can do those hills on PAS 1 in 3rd gear (of 8), PAS 2 in 5th or 6th, both with reasonable but not uncomfortable effort, or I can take them in top PAS 3 in high gear (20+ mph) with the same effort. I usually use PAS 1 or 2 depending on how tired I am getting. I think these hills are about 5% grade. But my point is, I have that much reserve power with the current ebike. If I still could pedal the hills on the mid drive ebike with top assist at 20 mph, then I'd know I am not giving anything up (again, not that I would go that fast, but it's nice to have some power in reserve in case I am someday pedaling an even steeper grade... like, if I went up Cadillac Mountain in Acadia NP, which has a "steepest quarter mile" of 7.4% and a little bit of the climb is in the 10%-15% range.
15" grade is no big deal on my Bosch. when I say grades I got up 18% grades every day and and one 20% grade almost every day. with the mid drive we can do that on our tandem too. it takes effort but its doable. I have done 1700 feet of climbing in less than 10 miles before.
 
Mid drives do the job. 'nuff said.

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power rating doesn’t have too much impact on hill climbing at low speed for a hub motor - a hub motor is not likely producing peak power when it’s only turning at 60rpm externally - unless the peak torque is only achieved at very low RPMs.

my first hand experience is that either a low power hub drive or a low power mid drive can climb hills, but the mid will do it faster because it stays closer to peak power at low speeds - since you’re hopefully always pedaling at a similar cadence regardless of how fast you’re going. without getting me too terribly worked up my low power rear hub drive can take me up 15% grades, and it’s rated at 250w or something and producing quite a bit less than that at speeds below 10mph. I can’t imagine a 750w unit wouldn’t be more than capable, assuming good heat management.
 
the mid will do it faster because it stays closer to peak power at low speeds - since you’re hopefully always pedaling at a similar cadence regardless of how fast you’re going.
I'd never thought of that. It makes sense to me, though, now that you tell me. I've noticed the sound the hub motor makes, of course, and the pitch gets higher as the forward speed increases. But a mid drive motor's speed is related to pedal cadence, not forward speed. Wow, yeah.
 
BTW, I looked up the gear inches on my R1Up LMTD. The range is 41 to 118. No wonder it's such a slug when pedaled up any incline without PAS.

The ebike I'm looking to get is a (used but like new) Electra Townie 8i. (I miss the crank-forward geometry of my old Trek Pure Sport.) If I've figured correctly, the range will be 26 to 81. That by itself will make a big difference versus the LMTD. So I give up some on the top end, no big deal to me.
 
I'd never thought of that. It makes sense to me, though, now that you tell me. I've noticed the sound the hub motor makes, of course, and the pitch gets higher as the forward speed increases. But a mid drive motor's speed is related to pedal cadence, not forward speed. Wow, yeah.
the opposite end is even more true! if the hub motor is really happy and in the sweet spot of the torque curve at 100rpm, how happy will it be at 250 RPM, which is 20mph…

of course, electric motors are pretty amazing in their flat torque curves over a much wider range of speed than combustion engines, but they absolutely have a range that their internal gearing is tailored to, and once you get past it, power and efficiency drop fast. this is why derestricting some of the low power hub drives doesn’t do much, they simply don’t make good power >300 external RPM.
 
I climb up to 15% with a 1000 w geared hub drive on the front. I carry 60 lb groceries, the bike with spares weighs 94 lb, I am 160 lb. It will start from a dead stop with no help and pull up to 6 mph on that grade. If I hit the grade at 25 mph it will be at 10 or higher at the top (100'). With 12 windings in 26" wheels It will not pull faster than 23 mph on the flat. The manufacturer (MAC) warns to not lug the motor at low speed for an hour, it will burn the winding. Mid drives cool better than geared hub drives. I have 77 hills on my 30 mile commute to summer camp which I ride in 3.7 hours. Personally I don't want to go faster than 25 mph. I just want to pull faster than 4.5 mph (unpowered) into a 20 mph headwind.
If one wants speed on the flat DD hub motors are more the thing. They will climb hills but use waaay too many watthours doing so, compared to a geared hub. WIth the patented batteries of mid-drives costing 2X what generic batteries cost, most mid-drives lacking a throttle for twisted knee days, and all mids requiring a display that gets in the way of flipping the bike to change a tube, I have never been tempted to buy a mid drive. I changed a tube and tire on the hub motor wheel 3 weeks ago in a pouring rain in 30 minutes.
 
The thing that might have been overlooked here is the motor manufacturers often give the motor power as its electric figure. I'd say the efficiency of a good motor rarely even reaches 80%. If that's true, the 750 W motor might actually deliver only 750 * 0.8 = 600 W max mechanical power (if the proper rpm of that motor can even be achieved on the climb).

The Specialized 2.2 mid-drive motor of 250 W nominal power actually delivers 565 W mechanical max. Electrically, the power draw is 565/0.8 = 706 W. During the climb, the e-bike transmission is used, so the mid-drive motor can spin fast and effectively while high torque is delivered by the drivetrain at the rear wheel, making the climb easy.

Hub-drive motors can overheat on steep long climbs while mid-drive motors do not.
 
The easiest way to increase hub motor climbing ability is to fit a smaller wheel.
I run a 24 inch on my hub drive, those 20 inch fat tyred mini bikes climb well at low power, you are simply lowering the gear ratio.
 
The easiest way to increase hub motor climbing ability is to fit a smaller wheel.
I run a 24 inch on my hub drive, those 20 inch fat tyred mini bikes climb well at low power, you are simply lowering the gear ratio.
The EBR reviewier said that about the 2020 Radrunner. He also said that putting the battery under the seat balanced the bike, and fat tires made it stable. I was skeptical, but I bought one based on the performance he demonstrated.

Mine climbed poorly. I went back to the part of the video where he said he was climbing a hill on throttle alone because his knees couldn't handle pedaling. I determined the grade when he turned his camera to a house whose front yard was on the same slope as the street. I determined his speed by the cadence of two Radrunners he passed. He had to be using a controller of at least 35 amps, more than twice what the OE controller put out. A 35 amp controller vastly improved climbing.

Here's why I was skeptical when he claimed the 20-inch wheels meant more torque. The diameter designation really means the tire fits a 16 inch rim. I found that the center of the axle was 11.5 inches from the ground, so the diameter was 23 inches on account of the fat tires. That's only 11.5% smaller than a conventional 26 inch tire. and it might be 4.2% smaller than your 24-inch tires.
 
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Why don't you carry the Bafang BBSXX mid-drive kits?​

We get this question several times a week and feel that it's worth devoting a page to the subject.

The Bafang mid-drives have become quite popular since they were first introduced as an aftermarket kit option around 2013. Prior to that, most of the mid-drive systms were designed for OEM bike frames and so not accessible to DIY conversions, or those that were meant for aftermarket installations were usually interesting but mechanically complex. The BBS01 design (which Bafang cloned from Sunstar) was neatly integrated as a self contained bottom bracket replacement without all the external mounting hardware, chains, pulleys etc normally associated with mid-motors.

In any case we've had samples of all the BBSxx motors and many variants from other manufacturers but have never felt that they hit the right note for what the majority of our customers are actually after. Integrated controllers limit your upgrade and repair options, wide 'Q' factor cranks to clear the motor can make for awkward pedaling, there have been limited chainring options, not to mention some messy politics in the distribution channel if you've been following that. We have been actively involved in mid-drive solutions for cargo ebikes with the Stokemonkey and varients, just not at the moment for regular bicycles.

Where do BBSxx and similar mid-drives shine?​

There are a certain areas where bottom bracket middrive motors are hands down better suited than hub motors. Offroad mountain biking is one great example. The motor weight is low and on the unsprung frame so it has minimal effect on handling even in full suspension bikes. In these situations you are often going slowly uphill through trails with short steep sections and a small motor working through the drivechain in the granny gears of the bike can do this with excellent efficiency. Another example would be say fat bikes riding in sandy beaches or through fresh snow. These are areas where the bike is moving at lowish speeds through high resistance terrain, and the mid-motor in an easy gearing will do this with better efficiency than most hubs drives, while still performing just as well on the faster roads.

For us though, a majority of our customers are using their ebikes for daily use commuting, riding on roads where maintaining a steady speed regardless of the hill grade is important. For that requirement a mid-drive offers almost no advantage and we continue to believe that hub motor kits shine the strongest for reliable and low maintenance commuter ebike conversions, and that's the bulk of who we serve.

Hub Motor Advantages​

Here are a few benefits to a hub motor system to keep in mind and help inform your decision. Please don't see this as us taking sides and saying that hub motors are universally better than mid-drive motors, all we want to do is balance out the discussion a little by highlighting the many benefits of a hub motor drive which are frequently missing from popular discourse at the moment.

1) Independent propulsion​

This point is often overlooked, but a hub motor has significant robustness in being totally independent of the human drivechain. If you've ever had a situation where a chain breaks, derailleur gets jammed, wet snow packs into the sprockets, freewheel busts apart etc. you become quite grateful that the hub motor can continue to propel the bike to get you home. With a mid-drive motor, anything that takes the drivechain out of commission stops the bike completely as both the motor and pedals become useless.

2) Less stress and wear on drivechain​

Chain stretch and cog wear


With a hub motor bike, the use of the motor lessens the mechanical wear and tear on the chain, cogs, and derailleur system, since it decreases pedal stress that the rider would otherwise put on the transmission. A mid-drive motor does the opposite, putting much more force on the chain and cogs with the motor propulsion now added on top of the rider's input. A normal bike chain drive is fairly robust and can usually handle this extra load without failure, but will wear out at a much faster rate, requiring more vigilant attention to chain stretch, cog wear, shifter alignment etc.


3) Ability to use internal gear hubs (IGH)​

Internal Gear Hubs work great with front hub motors


This is somewhat related to the above point, but one of the great innovations in bicycle hardware in the past decade has been the production of compact internal gear hubs that are 7-14 speeds with wide gear ranges. With a few exceptions (Rohlhoff and the original Nuvinci N171) these hubs are not rated for the extra stress of a motor drive and will usually have a short service life with more than an extra couple hundred watts from a motor. If you want to use a mid-drive with an internal gear hub, be sure to check whether the hub is rated for tandem and/or cargo use, most explicitly say no.


4) Higher peak power capability​

The transmission through your bicycle drivechain also limits the maximum motor power that can be coupled to the wheels. Power levels in the 250-750 watt range are usually fine just with increased wear and tear, but when you are looking for multiple kW of power then you start seeing catastrophic failures with snapped chains, sheared freewheels, broken spokes etc. A hub motor with a properly coupled torque arm has no such limitation.

5) Potential for regenerative braking​

Regenerative Braking, not an option with mid-drives
With a direct drive hub motor or a geared hub motor that has a locked clutch, the motor can act as a perfectly controllable brake that isn't affected by rain, pad wear, cable adjustment or anything like that. In a similar manner to how a hub motor reduces wear and maintenance on the pedal drive chain, it can reduce and even eliminate brake pad maintenance as well. You can easily do 90% of your braking electronically with only the odd emergency stop needing the mechanical engagement. On a mid-drive motor, there is really no potential for regen (unless of course you electrify a fixie, but we don't see much of that).


6) Ease of installation​

Admittedly the BBSXX systems and clones are pretty straightforward to install if you have bottom bracket removal tools and crank tools. But nothing gets quite as easy to fit as a front hub motor, where you are just taking off the original wheel and replacing it with a motorized one. In general we wouldn't emphasize this too much, as the time spent installing any conversion kit is way less than the time you save from riding it and you should install the system that is right for you. If you are concerned about installation and the facility of moving the assist to different bicycles and such, it's hard to top a front hub motor for minimal hassle.

7) Torque sensors options​

Just about every pedal torque sensing technology works with hub motors
Because of the independent propulsion, the hub motor drive leaves any number of sensor technologies available for measuring rider pedal input, including chain tension (BeamTS), rear dropout (TMM4), Rear axle flex (eg BionX), and the many bottom bracket torque sensors (NCTE, Thun, TDCM, Sempu etc.). With a mid-drive, the motor couples through the drivechain so these sensors can'd distinguish pedal power from motor power, and so you are stuck with what the mid-drive system comes with which has so far been pretty limited. Some (like lightningrods and Tongsheng) have a torque sensing, while on the vast majority they are have just a basic pedal cadence sensor.

Now there is no reason why more aftermarket bbs style mid-drive can't have an integrated torque sensor, it's just that so far this mostly exists only on OEM bottom bracket drives like the Bosch. .


8) Simpler operation with shifting​

For a mid-motor to work well the rider needs to shift through the gears as they speed up and slow down, and similarly back off on the motor power while shifting to avoid seriously harsh shift transitions. This constant backing off and reapplying motor power between each change of gears can get taxing and results in some speed loss too, while with a hub motor you can continue to have uninterrupted power through all your gear transitions. There are shift sensor products to make these motor cutouts automatic, but there is nothing you can do if you come to a stop in a mid-drive system and forget to downshift first. The motor will start off in a high gear with low acceleration and efficiency. For regular cyclists this is probably no issue, but for those without that background, the simplicity of not having to shift gears all the time is one big appeal of an ebike. The rider can generally leave the bike in a high gear and use the hub motor to quickly get up to speed so there is no need to go through the motions of downshifting and up-shifting at each stop and go.

Remarks​

So, we hope that this sheds some more light on why we've largely stuck to hub motor systems since first becoming enamoured with the Crystalyte 400 motors in 2003. If you've read on websites or forums that hub motors are "yesterday's news" with poor efficiency and handling, and mid-drive systems are the only way to go for an ebike, perhaps you'll have a more informed outlook after reading this.

Mid-drive systems are not some new technology (most ebikes from the 1990's and early 2000's like the Merida Power Cycle and Giant Lafree were mid-drives), and hub motors continue to evolve to higher levels of power density, efficiency, and bike compatibility since they first rose to prominence in the mid to late 2000's.
 
Why do they call the Specialized 2.2 a 250 W motor?
It is for legal reasons. It's called "nominal continuous motor power". 565 W is the peak power. Indeed, a Specialized 2.2 motor in Turbo mode feels like it were lifting you up a steep hill! The motor in my Vado 6.0 is 520 W max mechanical peak power. As I was climbing an overpass im Turbo mode, there was a traditional cyclist who was climbing faster than I could. After we stopped, I asked 'An impressive feat! What is your peak leg power?' to which he smiled and said '800 W?' :)
 
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