hill climbing? 750W hub versus 250W mid drive

[Rexlion]

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!

 

[Chargeride]

Mid drives are not 250w, that's a nominal figure.
You get up to 800w in a legal bike.

750w hub drives usually run a 15Amp controller and are nearer that actual power output.

A mid drive is always a better climber at these power levels.

 

[CodyDog]

I prefer a mid drive over a hub drive for climbing. I have owned both.

 

[gromike]

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.

 

[Rexlion]

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.

 

[fooferdoggie]

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.

 

[Rexlion]

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.

 

[Rexlion]

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.

 

[fooferdoggie]

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.

 

[Mr. Coffee]

Mid drives do the job. 'nuff said.

Rendezvous Pass and Third Creek Road

35.9 mi, +3774 ft. Bike ride in Okanogan County, WA

ridewithgps.com

 

[mschwett]

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.

 

[Rexlion]

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.

 

[Rexlion]

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.

 

[mschwett]

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.

 

[indianajo]

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.

 

[spokewrench]

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!

Torque varies inversely with speed. When I bought my Radrunner, I found a driveway that it would barely climb, at walking speed. They advertised 80 nm, but this was only 53. Next, I tried a public street that it would climb at 11 mph. That amounted to 25 nm and 500 watts. When Radpower advertises 750 watts, they mean electrical input, not mechanical output. A 35 A controller doubled its climbing speed.

If you want to climb a hill faster than walking speed, watts is what counts. A 250 W middrive would climb faster than a 750 W hub only if the former were actually producing more power than the latter.

 

[Stefan Mikes]

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.

 

[Chargeride]

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.

 

[spokewrench]

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.

According to curves I've seen, ebike motor is between 66 and 80% efficient as long as it's turning at least half as fast as its maximum. Radpower seems to mean electrical input. I believe Bafang, Aventon, and Sixthreezero mean mechanical output.

Why do they call the Specialized 2.2 a 250 W motor? It's made for mountain biking, where one is likely to encounter grades that one would not find on a public road. 565 watts could lift a gross weight of 300 pounds at 1.4 foot per second. That would be about 19 mph on a 5% grade. Rolling resistance and air drag might bring it down to 15 mph, and it wouldn't matter much if you had a mid drive or a hub motor of 565 watts' output.

If your hub motor produces 80 nm, that would be 225 newtons on a 28 inch wheel. That would take you up a 16% grade, but to produce that torque, the motor would slow to a crawl. It could take a long time to climb the hill at a crawl, and the motor would be heating with a wattage equal to the square of the amps times the ohms of the wire. Switching from 36 to 48 volts can reduce heating by 44% for the same output. A motor with one gauge larger wire reduces heating by 21%.

A mid drive can avoid the problem by letting the motor put more torque on a slower wheel without bogging down. On public roads, I've done fine with hubs. On my Rad bikes, I doubled the amps (and climbing ability) with aftermarket controllers. Temperature rises have been negligible.

 

[spokewrench]

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.