hill climbing? 750W hub versus 250W mid drive

[gromike]

And I'll add to the above that I prefer a rear direct-drive hub motor. The only downside for me is that dang heavy rear wheel. With pedaling I can fly up the hills. My biggest hub motor is labeled at 500w, but is fed up to 1440w. It helps that it's in a 3x9 gearset bike.
With direct-drive hub motors the mantra is more amps!

 

[gromike]

....that is until you smell that smell.

 

[Fingers]

Back to my engineering point of view...power is power, and, as you might already realize, if you want to do less work, or go faster, more power is better! No argument there.

Now, for some simple math. 1 hp = 745.7 Watts This means that a 750W motor is about1 hp, so a 500W motor is about 2/3rds of a hp, and a 250W motor is about a 1/3rd hp. The average human (in decent physical shape) can put out about 1.5 hp instantaneously (like a dead lift), 1 hp for about 1 minute and .5 hp indefinitely. [I am familiar with these numbers because for many years I was heavily involved with HPVs of all types.] And hp = torque x RPM. What does this mean? If you want more hp going to the rear wheel, just pedal harder [more torque] or pedal faster [more RPMs]. This also means that with limited power, and you want to increase torque to the rear wheel, you have to lower the gear ratio. This also means that if you want more power than you can provide, just get a bigger motor. I [myself] just use longer cranks to increase my torque to the rear wheel. (It also doesn't help that I weigh more than 25 kg than my wife!)

I do wish we had a throttles on our e-bikes, because without one it makes a huge difference where and when you come to a stop. Stopping on a steep, uphill grade can make your ride interesting when it comes time to get back on and to get going again. Some of the better mid-drive e-bikes do have a 'temporary motor boost' on their controls (just for starting up hills) but [as far as I can tell] ours do not.

All this really means is that any e-bike is what you want to make of it. We prefer the 250W motor because it means we still have to do some work, and after the age of 65, the amount of physical exercise you get in on a daily basis makes a difference. I also like to brag that 'no matter how I feel first thing in the morning when I get on my bike, I have a button [power setting] for that!'

 

[kevinmccune]

the biggest factor in my opinion is controller amps,the stepped down small middrive motors can be great or mediocre, one advantage of a middrive if that wheel moves at all the little motor is starting to spin at a good rate,the old hub motors are usually grunting at a low speed( probably getting eddy heat as well) for my uses hub drives are just fine if the controller will give the motor a little juice,some really powerful ev vehicles have little in the way of gearing the big diesel electric locomotives do not use much in the way of gearing i am led to believe,thats the big advantage of an electric motor,its simplicity and flexibility,go middrive for light weight if weight doesnt matter do not overlook the hub drives i have had good luch with any dd setup i have built,they slot nicely into my preferred spd range. one thing coming down the pike will be more advanced cassette less bikes or basically single speed belt assisted ebikes, the simplier the better if you do not care to maintain.

 

[spokewrench]

I do wish we had a throttles on our e-bikes, because without one it makes a huge difference where and when you come to a stop. Stopping on a steep, uphill grade can make your ride interesting when it comes time to get back on and to get going again. Some of the better mid-drive e-bikes do have a 'temporary motor boost' on their controls (just for starting up hills) but [as far as I can tell] ours do not.

All this really means is that any e-bike is what you want to make of it. We prefer the 250W motor because it means we still have to do some work, and after the age of 65, the amount of physical exercise you get in on a daily basis makes a difference. I also like to brag that 'no matter how I feel first thing in the morning when I get on my bike, I have a button [power setting] for that!'

When I bought my first e-bike, I thought of electric motors as being nearly 100% efficient. I found a hill where on motor alone it would accelerate to a certain speed and no faster. With no speedometer, I marked 50 yards and used a stop watch to see what that speed was: 11 mph. That was a good test speed because in still air, there would have been little aerodynamic drag, and it was fast enough for the 20mph motor to produce nearly its maximum power.

I knew my gross weight, measured the grade, and found that the motor was producing about 2/3 hp or 500 watts. I believe a motor rated at 750 watts is supposed to produce 750 mechanical watts indefinitely without overheating, but Radpower meant their controller was feeding the motor 750 watts. That’s like saying a 100 hp gasoline engine is one that can burn 2.23 gallons of gasoline an hour.

I couldn’t climb that hill faster because going faster would mean less torque. An e-bike motor produces maximum horsepower at a speed where torque has dropped to about a third of its maximum. If you ride where hills often slow you way down, a mid drive would, by letting you maintain an efficient motor speed, greatly increase battery range and reduce heating.

My newest e-bike came with torque-sensor PAS. At its lowest setting it gave me much more assistance than I wanted, and if I turned PAS off, the throttle didn’t work. When the BB bearings acted up, I installed a bottom bracket with no torque sensor and changed the lever throttle for a half twist-throttle. It’s much better than PAS. Mostly, I pedal without assistance, but if I’m slowing on a grade, I can use the throttle momentarily to bring my speed back up or continually to add just a little assistance.

Throttle without PAS is very helpful when pedaling for exercise. In April, I was going about 300 miles per charge, meaning my legs were generating almost all the energy. In July, when the pavement could be 145 F and the dew point 74 F, I was getting about 150 miles per charge. I depended more on the throttle to stay cooler instead of producing all that kinetic energy myself. Even if I were to use the motor continuously, pedaling would let me minimize the amount of throttle and still maintain an efficient speed for the hub motor.

 

[Jeremy McCreary]

My newest e-bike came with torque-sensor PAS. At its lowest setting it gave me much more assistance than I wanted, and if I turned PAS off, the throttle didn’t work. When the BB bearings acted up, I installed a bottom bracket with no torque sensor and changed the lever throttle for a half twist-throttle. It’s much better than PAS. Mostly, I pedal without assistance, but if I’m slowing on a grade, I can use the throttle momentarily to bring my speed back up or continually to add just a little assistance.

Throttle without PAS is very helpful when pedaling for exercise. In April, I was going about 300 miles per charge, meaning my legs were generating almost all the energy. In July, when the pavement could be 145 F and the dew point 74 F, I was getting about 150 miles per charge. I depended more on the throttle to stay cooler instead of producing all that kinetic energy myself. Even if I were to use the motor continuously, pedaling would let me minimize the amount of throttle and still maintain an efficient speed for the hub momotor.

Sounds like we have similar riding habits. The torque-sensing assist on my 500W, 65 Nm hub-drive is nicely implemented. But like you, I wanted less help at lowest assist.

Luckily, my display menu offers an easy solution. The bike comes set for 5 non-zero assist levels with options for 3, 6, and 9. Stock lowest assist 1/5 was too much, but significantly lower 1/9 is just right.

The "throttle on top of pedaling" option you mentioned deserves more attention. To take full advantage, you need torque-sensing assist and a progressive throttle that simply adds metered power to whatever the assist is doing at the time.

Yes, you could just up the assist, but the throttled power boost is instant, precise, and totally predictable in both timing and amplitude. Often more convenient as well. And pedaling all the while.

Among many other things, great for keeping cadence and speed over brief ostacles like steep driveways or roots on trail climbs. And as you noted, for keeping up hub motor (= wheel) speed on climbs that would otherwise bog the motor down. A few seconds of throttle on top of pedaling is usually all it takes.

In short, I see my throttle as an occasional adjunct to pedaling, not as a substitute. With knees that don't like strong accelerations, giving up this functionality for the advantages of a mid-drive is a tough sell.