At what gradient does cycling stop being efficient?

unCivilServant

Father Jack wrote:

put 20kg on a backpack then walk up a 400' hill. Then put 20kg on bike pannier and go up the same hill in 1st gear. Even with the extra weight of the bike, it'll still be easier on the bike.

Funnily enough, I've actually moreorless done this over the years (lots of trekking in mountains), most recently bike touring this year.

I'm hopeless at cycling hills: can't ride up anything more than about 10% for more than a few metres, whereas I can walk uphill indefinitely at 3.5mph.

This summer in Applecross I met a bloke who'd cycled all the way up to the Bealach na Ba, unladen. He'd done it in 2hrs; didn't say how much time of this was sightseeing, but I assume minimal.

So then I went up there with full touring (camping etc) gear. Thanks to the load, and especially being rubbish at hills, I walked over half of the way. And did it in...1hr45.

deptfordmarmoset

unCivilServant wrote:

Father Jack wrote:

put 20kg on a backpack then walk up a 400' hill. Then put 20kg on bike pannier and go up the same hill in 1st gear. Even with the extra weight of the bike, it'll still be easier on the bike.

Funnily enough, I've actually moreorless done this over the years (lots of trekking in mountains), most recently bike touring this year.

I'm hopeless at cycling hills: can't ride up anything more than about 10% for more than a few metres, whereas I can walk uphill indefinitely at 3.5mph.

This summer in Applecross I met a bloke who'd cycled all the way up to the Bealach na Ba, unladen. He'd done it in 2hrs; didn't say how much time of this was sightseeing, but I assume minimal.

So then I went up there with full touring (camping etc) gear. Thanks to the load, and especially being rubbish at hills, I walked over half of the way. And did it in...1hr45.

And if you take into account the return times, given that an up gradient is also a down gradient looked at from the other way, only looking at the uphill part will skew times - the OP hasn't explicitly specified ''uphill gradients''. Part of the energy expended cycling up will be released downhill on the return journey - this is one of the cyclist's greatest rewards. In nearly all cases, the downhill journey times will far, far quicker on a bike than they would be for a walker.

DaSy

cougie wrote:

Blimey Dasy - averaging 6.5mph up Ventoux running is pretty damn good. Whats her 10k time ?

She doesn't really do 10K, she's an elite marathon runner, around 3 hours for a marathon...she's a lot better runner than I am cyclist, I know that much!

22k up to the summit, took a picture of herself and the random dog she had tag along with her from just outside Bedoin, turned around and ran back down! She did this as a kind of impromptu thing too, had not planned to run up it until we got there, and said she thought she'd give it a whirl.

rick_chasey

deptfordmarmoset wrote:

And if you take into account the return times, given that an up gradient is also a down gradient looked at from the other way, only looking at the uphill part will skew times - the OP hasn't explicitly specified ''uphill gradients''. Part of the energy expended cycling up will be released downhill on the return journey - this is one of the cyclist's greatest rewards. In nearly all cases, the downhill journey times will far, far quicker on a bike than they would be for a walker.

I'm not talking about the return journey.

For all we know the most efficient way would be to climb up the mountain on a bike and then base jump off the top if you're looking for most efficient up and down.

All I want to know is, variables included, beyond what gradient uphill, do you travel a further distance (in total, not just height gained) for a given effort, when using a non-cycling human powered way of travelling? Such as, say, walking/running, climbing, etc.

stigofthedump

When climbing hill you use energy moving forwards and you store energy as gravitational potential energy, GPE.
A quick search of the web reveals that a 90kg person cycling at 9km/hfor 30 mins requires 171 Kcal or 718 kilojoules of energy. The same person running at 9 km/h for an hour requires 421 Kcal or 1770 kilojoules.
The cyclist also needs to get their bike up the hill, this requires some energy too, so the height at which the GPE of the bike is equal to the difference in energy requirement will give us the gradient where walking is easier.
The difference in energy is 1052 kilojoules and for a 20 kg bike this corresponds to a height gain of over 5000m in a distance of 4500m, ie further vertically than the distance travelled.
So cycling will never be less efficient than running.
Walking uses less energy than running so at slower speeds it could be more efficient.

Ben6899

DaSy wrote:

cougie wrote:

Blimey Dasy - averaging 6.5mph up Ventoux running is pretty damn good. Whats her 10k time ?

She doesn't really do 10K, she's an elite marathon runner, around 3 hours for a marathon...she's a lot better runner than I am cyclist, I know that much!

22k up to the summit, took a picture of herself and the random dog she had tag along with her from just outside Bedoin, turned around and ran back down! She did this as a kind of impromptu thing too, had not planned to run up it until we got there, and said she thought she'd give it a whirl.

Impressive. I can run a bit, but...

prb007

DaSy wrote:

cougie wrote:

Blimey Dasy - averaging 6.5mph up Ventoux running is pretty damn good. Whats her 10k time ?

She doesn't really do 10K, she's an elite marathon runner, around 3 hours for a marathon...she's a lot better runner than I am cyclist, I know that much!

22k up to the summit, took a picture of herself and the random dog she had tag along with her from just outside Bedoin, turned around and ran back down! She did this as a kind of impromptu thing too, had not planned to run up it until we got there, and said she thought she'd give it a whirl.

You should start a new thread......
'how fit is YOUR bird?!'

bicyclepirate

Surely going up a hill has nothing to do with it. Whichever way you go up the hill you change your mechanical energy into potential energy. And the more efficient the use of mechanical energy the more potential energy that is captured. Bicycles are more efficient that not bicycles. So if you biked up you'll have wasted less lost energy and therefore been more efficient.

Valy

stigofthedump wrote:

When climbing hill you use energy moving forwards and you store energy as gravitational potential energy, GPE.
A quick search of the web reveals that a 90kg person cycling at 9km/hfor 30 mins requires 171 Kcal or 718 kilojoules of energy. The same person running at 9 km/h for an hour requires 421 Kcal or 1770 kilojoules.
The cyclist also needs to get their bike up the hill, this requires some energy too, so the height at which the GPE of the bike is equal to the difference in energy requirement will give us the gradient where walking is easier.
The difference in energy is 1052 kilojoules and for a 20 kg bike this corresponds to a height gain of over 5000m in a distance of 4500m, ie further vertically than the distance travelled.
So cycling will never be less efficient than running.
Walking uses less energy than running so at slower speeds it could be more efficient.

That's assuming you are limited by the height Hahahahaaaaaaa!
______________________________

Kind of intrstn thread though.

rick_chasey

bicyclepirate wrote:

Surely going up a hill has nothing to do with it. Whichever way you go up the hill you change your mechanical energy into potential energy. And the more efficient the use of mechanical energy the more potential energy that is captured. Bicycles are more efficient that not bicycles. So if you biked up you'll have wasted less lost energy and therefore been more efficient.

*facepalm*

OK, let me rephrase.

You want to get from A to B right?

B is much higher than A, much higher.

At what gradent would the road be, from A to B, to make another form of human powered transport, whether it be running, walking, climbing, going up a rope, rowing, swimming, whatever, quicker for the same effort.

Of course any energy you put in is going into GPE, but, since we're only going up, and not back down, in this instance, the GPE counts as energy wasted, since it's not being turned into energy moving you along.

I'll give you an example. If you try and run along a full pelt peleton on the flat, you won't keep up. Run along a pro gonig fill tilt up the Tourmalet, you might keep up for a bit. On the Zoncalon, probably you'd be able to run alongside for even longer. Etc.

tx14

simple physics here.

on a bike, you mostly work against air resistance, which is proportional to speed squared.
running and walking, you have your center of mass bobbing up and down, which cost a lot of energy, and air resistance, although typically much weaker.
gradient doesn't matter that much, you still need to lift your body weight up the same distance, only difference is 9kg of bike.
if your question is which method takes the least energy to get from A to B, B being higher than A. you need to consider the speed of the rider, the faster he is, the less efficient he is, since the work done against air resistance is proportional to speed squared.

in a special case, as someone else pointed out, if the same person rides up and runs up the hill at the same speed, then the bike is definitely more efficient.

rgisme

Walking becomes more efficient at the point where you can no longer ride it faster than you can walk it!

unCivilServant

deptfordmarmoset wrote:

And if you take into account the return times, given that an up gradient is also a down gradient looked at from the other way, only looking at the uphill part will skew times - the OP hasn't explicitly specified ''uphill gradients''. Part of the energy expended cycling up will be released downhill on the return journey - this is one of the cyclist's greatest rewards. In nearly all cases, the downhill journey times will far, far quicker on a bike than they would be for a walker.

Funnily enough also, in this respect too my Bealach Na Ba adventure didn't quite conform to received wisdom...

To cut a long description short, combined factors around my bike brakes and general cautiousness mean I generally have to walk down the steepest gradients as well as up them. Too much fear of the "far, far quicker downhill journey times" being terminal velocity off a sheer drop/into a car/sheep!