What is it about rolling a bicycle up a hill that's so hard?

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swbluto

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So, there's this 15% hill right? This is something that I could ordinarily carry my 200 pound body up quite fine at 2.5 mph-3.5 mph at a fairly steady pace. So, I try going up this hill with my bike that itself weighs an additional 70 pounds and, my god, I had to take three rest stops of like 5 minutes each to get to the top, and that was after climbing a measly 50 feet up per rest stop!

When I'm thinking another 70 pounds, I'm imagining about loading myself with 70 pounds of books or something and compared to my current body weight, it seems like it'd be fairly easy to climb. But, for some reason, it felt impossible with an electric bike. Is there something about the "continuous pulling" of a wheeled-object on a hill that significantly increases the difficulty, as opposed to the "no-load" of a person when simply standing? That is, if the person were stopped, they wouldn't naturally just start being pulled down the hill and it requires little exertion to stop, but a bicycle would.
 
Try it. Try walking up the same hill at 3.5mph with 70 pounds of books, maybe it is harder than you think?
 
vanilla ice said:
Try it. Try walking up the same hill at 3.5mph with 70 pounds of books, maybe it is harder than you think?
Click to expand...

From an energy point of view, it shouldn't be that much harder. That's only 1/3 more energy needed, and presumably 1/3 more power output to maintain the same speed. I don't really feel like I'm near maxing my power output just walking up a hill unloaded.
 
you will notice that the bike wants to go back while your pushing it making it that much harder.
 
Watch that it doesn't roll back at all as you make your steps.

70lbs of books would be a LOT. Even a 30lb backpack feels like a big load when climbing stairs.

You're also using your upper body quite a bit too - more muscles activated means higher heart rate. Pushing my reel mower through thick grass shoots my heart rate up quite fast. But pushing on the bike pedals for a bit doesn't push my heart rate up that quickly.
 
I'm guessing the sensation is simply different, walking versus riding. Riding you can easily roll backwards, with nothing preventing this, but walking there is a feeling of a stairstep or ratcheting effect, as you don't feel like you are sliding backwards if you just stop and rest.

The muscle motions are different as well; if you had a bike that stairstepped (pickup foot, slide backwards to simulate forward stepping) for input instead of circular pedalling, it'd probably feel about the same, if the bike was also ratcheting so that it could only roll forwards.
 
I suppose it has to do with approaching the limits of what the average guy can do. Just standing there on a hill of 15% would be pretty difficult with a 70 pound backpack. Most folks would not make it very far waliking up it with only 40 pounds of backpack. Putting the weight on a bike makes it much much easier, as the guys from north vietnam would testify, but it's still getting close to the limits of what human power can do for very long to carry 70 pounds up a steep hill even with a bike. There is a reason few materials are bagged in bigger sacks than 80 pounds, and most are bagged at 50 pounds.
 
There're more sophisticated calculators here for figuring stuff like Wh/km given lots of variables but here is a simple Java-based calculator intended for pedal bike folks (about 1/2 way down the page):
http://www.exploratorium.edu/cycling/aerodynamics1.html
Throw some numbers in there then try diff. values for slope and watch the watts change. EVen from zero to one degree the diff is pretty significant.

lLoK
 
Maybe you got a spot of bad gravity on that hill? That's what we used to blame spilling the beer on, a localized spot of bad gravity.
 
The bike mechanical system and ergonomy are not optimized, you lose part of your human power in the process, even with gear ratio to help you as much as possible. You will find, like anyone else, that at some point of climbing, it becomes suddenly easier to carry your bike up the hill than continuing to pedal; this is the point where the geometric ergonomy and mechanical optimization, reach their limit on your bike. This limit will be different for you, with different bikes, and different mechanic or geometric adjustments on one bike.

I am a newbie here, from Montreal and french speaking. This was my first contribution on the forum, I hope that it helps understanding how the ergonomic and mechanic design are important to improve performance. Then, if I start with giving one helping answer, I will be more likely to ask for help here. The reason to come here, is the project of building my first electric bike this winter, and I don't know sh*t about it. I never had one, and what I saw in the commerce is laughable; so I decided to build one, and learn everything about it in the process. Thanks to those who will take the time to answer my questions, I will start by reading the interesting subjects on this forum.
 
Madrhino, welcome to the forum and good luck on your project!

I had the same experience. I saw electric bike kits at shops, and some of them are very very bad. Others are perfect, but cost a lot of money. I wanted something inbetween the two extremes, customized to my liking. so here i am .. :)
 
neptronix said:
Madrhino, welcome to the forum and good luck on your project!

I had the same experience. I saw electric bike kits at shops, and some of them are very very bad. Others are perfect, but cost a lot of money. I wanted something inbetween the two extremes, customized to my liking. so here i am .. :)
Click to expand...
Thnx

I'm going for extreme, starting with a 5000$ DH, looking for performance on and off road. From what I read on this forum, I guess I'll find here everything I need, but sooo much to learn from the start.
 
well i tried an experiment yesterday on my 36 delivery bike,had to go get 2x double walled cardboard boxes and styro.so hill is grade 7.weight of bicycle loaded about 60 lbs.
walking up no problem.riding up in low gear pretty good.pushing getting difficult.i have noticed that your weight is shifted to the bicycle and the bicycle rolls back on a hill making more resistance.so without science graphs involved, pushing a heavy bicycle up a hill is harder to do because you shift your weight towards the handlebar and gravity pulls the bicycle down with part of your weight on the bicycle.that is as scientific as i can get. but real life situation is the best. :D
 
Yeah, even on an ebike, ergonomics plays a huge role. I can't wait to see what you eventually build if your budget for the donor bike is $5000. :D

For the best possible performance, you'll need to hang out in the non hub motor sections a lot. I have one of the better hubmotors for a dirt bike, and though it's plenty nice to me, it's at best a poor compromise. Hubmotors are just too heavy on the wheel. Nothing wrong with some preliminary experiments with hub motors to gain experience with batteries and such though. Such experiments might best be done on a much cheaper bike too, with steel in the rear swingarm. A mongoose blackcomb might be a good bike to trash while learning the don'ts.

And learn about lipo, or A123 batteries. Don't bother with anything less powerfull. Welcome to the sphere, and have fun!
 
beast775 said:
pushing a heavy bicycle up a hill is harder to do because you shift your weight towards the handlebar and gravity pulls the bicycle down with part of your weight on the bicycle.
Click to expand...
That's part of what I meant when I referred to having a ratcheting wheel helping with that problem. Basically like having a freewheel for the wheel itself, that only freewheels in the forward direction, preventing the bike from rolling backwards at all.

FWIW, CrazyBike2's current drivetrain is a little like that, in that it is very hard to roll it backwards due to the non-freewheeling motor that is on the drivetrain, because of the reduction gearbox on that motor plus the motor itself (and the controller's regen circuitry/etc. probably).
 
Good one TD, since retro-direct can't roll backward.

I'll do one better since in the past year I've walked a hundred pound ebike up hill several times in the past year, and it was even easier than walking up without the bike. 8)
 
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