?? Cadence versus torque and power, any data?

[axel_knutt]

What exactly are you trying to achieve, are you aware that maximum power is not the same as maximum efficiency? Unless you're a racing cyclist sprinting for the line, the latter is usually more important than the former.

I also can’t understand why the curve doesn’t show high power and torque at very low cadence

Because power is torque x cadence, and cadence is low not because it produces more power, but because....

you’ve got no lower gears left

The reason you stall on a steep hill is precisely because you can't produce the necessary power at such low cadence, because the low cadence necessitates a torque/force so high that it's beyond the capability of your muscles. Conversely, power falls off as cadence gets higher and higher is because you can't continue to exert the same force, not least because more and more of your muscle force is consumed in accelerating your leg mass up and down.

[Nearholmer]

Yes, I’d been ruminating on that since posting it, and you are right about it being impossible to deliver maximum output (at the crankshaft) power at very low cadence.

Why I think it feels counterintuitive is because one can, indeed does, achieve maximum input power in the conditions I describe ….. fuel being consumed at a prodigious rate, heart and lungs going full ….. but a lot of it just gets converted into heat and bad language, because the body can’t convert it into useful output at that cadence.

Reinforces my developing plan to fit lower bottom gears to my (gravel) bike when I wear the present sets out, because I’m forever tackling climbs where I deploy lung-busting effort, but don’t make good use of it due to a combination of very low cadence and loss of adhesion, often I’ll wheel spin to a halt in a bath of sweat and swearing, sometimes I’ll simply run out of puff ….. I suspect that I stray a bit into MTB territory!

As to what Carlton is looking to discover from all this: I’d be interested to discover.

[Tigerbiten]

The graph I like is an efficiency one of effort vs cadence, I saw it once and cannot find it again.
Its made up buy adding two lines together.
The first line is.. How much effort do you need to push a pedal down. It's at it's max at zero cadence and it drops in a straight line to zero when the pedals start to spin faster than your legs can.
The second line is.. How much effort do you use to just spin your legs. It starts at zero and goes up at the square of the cadence.
This give you a nice U shaped line where your at your most efficient around the bottom of the U.
I've worked out that I'm at my most efficient around 70-80 RPH.
On hills I can easily drop to around 60 rpm and grind my way up.
But once my cadence hits around 90 rpm, my efficacy tanks and I cannot keep it up for long.

[Jdsk]

The graph I like is an efficiency one of effort vs cadence, I saw it once and cannot find it again.
Its made up buy adding two lines together.
The first line is.. How much effort do you need to push a pedal down. It's at it's max at zero cadence and it drops in a straight line to zero when the pedals start to spin faster than your legs can.
The second line is.. How much effort do you use to just spin your legs. It starts at zero and goes up at the square of the cadence.
This give you a nice U shaped line where your at your most efficient around the bottom of the U.
I've worked out that I'm at my most efficient around 70-80 RPH.
On hills I can easily drop to around 60 rpm and grind my way up.
But once my cadence hits around 90 rpm, my efficacy tanks and I cannot keep it up for long.

What do you mean by "effort"... force, power, metabolic rate, something else?

Thanks

Jonathan

[Nearholmer]

One of the puzzles of all this is, as I noted above, that effort in and measured power out at the crankshaft can be very different things if you get gear ratio wrong (as I clearly have been in some cases).

[Carlton green]

That one I think must be “idealised”.

Here’s a nice messy one for you:

IMG_2360.jpeg

Several of the others are simply curves, with no data points.

Thank you, these graphs are confirming to my mind that the torque exerted at the crank increases as cadence drops. So, for the same gear ratio, the rider’s ability to climb can actually be assisted by going slower because more force will be exerted on the cranks and transformed into chain-set torque. Torque and power shouldn’t be confused (I suspect that some who have been kind enough to respond have done so) they are different and peak at different points.

Tim Hughe’s book (Adventure Cycling) talks about hill climbing using a 30” gear at 45rpm, to my mind that goes against today’s wisdom were a lower gear and higher cadence would be suggested. However, for any sprocket on the back all that matters is chain tension and that can be increased by a smaller chainwheel and, as we now see, to some degree by pedalling more slowly.

[Jdsk]

...
Thank you, these graphs are confirming to my mind that the torque exerted at the crank increases as cadence drops. So, for the same gear ratio, the rider’s ability to climb can actually be assisted by going slower because more force will be exerted on the cranks and transformed into chain-set torque. Torque and power shouldn’t be confused (I suspect that some who have been kind enough to respond have done so) they are different and peak at different points.
...

Are you suggesting that "ability to climb" is limited by the power or by the torque delivered by the rider?

Thanks

Jonathan

[Carlton green]

...
Thank you, these graphs are confirming to my mind that the torque exerted at the crank increases as cadence drops. So, for the same gear ratio, the rider’s ability to climb can actually be assisted by going slower because more force will be exerted on the cranks and transformed into chain-set torque. Torque and power shouldn’t be confused (I suspect that some who have been kind enough to respond have done so) they are different and peak at different points.
...

Are you suggesting that "ability to climb" is limited by the power or by the torque delivered by the rider?

Thanks

Jonathan

The ability to keep going up a hill is limited by the torque at the back wheel, of course that’s subject to going fast enough not to fall off a bicycle.

For any common (effectively identical) gearing arrangement the torque generated at the crankshaft and back wheel appears to increase as the cadence drops.

Power and torque are two different things.

[Nearholmer]

I think there is an obsession with operating at highest achievable power level, because that ensures highest achievable speed, and much of the cycling world is very much speed oriented. Besides which, people like to brag about their power output!

However, there could be multiple goals other than speed;

- minimise energy consumption (running out of food on a tour in the wilds?), which goes to maximising efficiency;

- control HR to a particular level, because of the different fatigue effects of different HRs and a want to keep “something in the bank” for later;

- to get up it at all, or without grinding to a halt, which is often the game I play off-road, where picking a line, not getting wheel-spin, not bogging-in, not puffing yourself out in the first 100 yards etc all come into play.

I can’t quite see that developing maximum torque is an end in itself, though. Why would it be?

To me, it seems that the choice the rider makes on an ordinary road climb is how much power they wish to deploy: everything they can muster; or, something less for one reason or another. If something less, then operate at lower cadence than for maximal power, but not so low that momentum in the legs is lost and/or the legs simply don’t have the muscles to deliver each plodding turn of the pedals, or they maintain whatever cadence they are happiest at, dropping down through the gears to control their speed, and hence power.

[Carlton green]

We risk thread drift, which would be unfortunate as the original post and its objectives would benefit from more exploration.

I think that the pursuit of speed is over rated and over promoted; for me cycling isn’t a sport but rather an enjoyable activity and utility that transports me from one desired place to another. It’s certainly a physical activity though - you have to put effort in - so understanding how one’s body interacts with, powers and puts forces into the cycle is important.

My suspicion is that there is a minimum practical road speed and peddling cadence and that both are quite low - setting to one side the importance of momentum, etc. If you have a simple bike with a limited gear range, and are climbing a hill, then deciding to pedal slowly / slower actually gives you the advantage of naturally exerting more / additional torque at the crankshaft (which is rather important when you have no lower gear). So, as you cycle up a hill, your speed can drop and as it does so your crankshaft torque either naturally increases (with the lower cadence) or is overcome, because the low cadence torque is insufficient to balance the torque needed for any forward movement.

I’d really like to understand more the relationship of lower speed cadence - say to 25 rpm - and torque, the graphs so far only show a higher and limited range.

[Nearholmer]

I’d really like to understand more the relationship of lower speed cadence - say to 25 rpm - and torque, the graphs so far only show a higher and limited range.

Assuming that you maintain constant power, however much of your available power you’ve decided to deploy, as cadence falls, torque rises. You make fewer pedal strokes each minute, but the force applied within each gets greater. It’s all in the formula given right at the start.

However, for most people, pedalling below a certain cadence becomes significantly inefficient, so either the amount of input power has to rise to compensate (this extra input power doesn’t appear at the crankshaft, it simply warms the cyclist up), or they go even slower.

If very low cadence was the best way to pedal, the most efficient, we’d all do it all of the time, even on the flat, without even being taught to - we’d simply feel it to be the right thing to do. But we don’t, or at least very few people do, we use our gears to find a combination of cadence and torque that suits us as individuals.

I’m a fairly low cadence/high resistance rider, I like to feel something to push against, but there’s a chap who cycles to work past our house every day who is the complete opposite. His actual road speed is about the same as mine, but he rides exceptionally ‘light’, very high cadence and low torque …. To me his style looks weird and uncomfortable, and he probably looks at me and thinks the same!

[Tigerbiten]

A 30" gear spun at 45 rpm means your climbing out of the saddle at 4 mph.
I've done many an hour climbing many a hill like that way back when that was a "standard" 1st gear on a touring bike.
If you couldn't keep the pedals turning at around 45 rpm, you got off and walked.
Nowadays I'd only drop to around 60 rpm in a 22" gear and climb the same hill at the same speed seated.
If I couldn't keep the pedals turning at 60 rpm, I'd just drop to an even lower gear and just climb slower on my bent trike.
With a 9.6" 1st gear the limiting factor becomes traction between the tyre and road, if the back wheel just spins because I've no traction, I'm not going anywhere in a forward direction.

One thing I've learnt since getting the bent trike is that "spinning" doesn't mean cycling with an ultra high cadence.
It's more about keeping a light pressure on the pedals, which just happens to be easier to do at a higher cadence.
But I can spin up a hill 60 rpm, just like as I can spin along on the flat at 70-80 rpm simply because I keep the same pressure on the pedals.

[Carlton green]

Some interesting responses, thank you.

I’m still looking for more data, but perhaps there is none.

Techniques vary and, to my observation, there’s often more than one way to achieve objectives. Available technology also changes. Couple those two variables together and we get changes in style and fashion over the decades - as partly illustrated in the ‘historic’ Hughes book. To make better use of whatever you have it’s handy to have some knowledge and understanding of alternative and historic ways of using it.

For several reasons I’m not a fan of pushing high gears, I think it better to peddle at a moderate cadence in a lower gear. However, understanding why and how pushing a higher gear is effective - or can be - gives us additional options; I’m in favour of having options.

[cycle tramp]

..at this point you might want to look at what Mike Burrows wrote about the use of shortercranks and his observations..

...the thing is, it's not just about cadences and gearing, but because we're biological engines we've also got to examine crank length, latic acid build up in muscles, oxygen depletion in the blood and fast and slow twitch muscle fibres....

[Nearholmer]

Possibly the best way to understand this is with your legs and lungs, by finding a hill of suitable gradient and length, and going up it using different gears/cadences.

There’s a pair of steep and difficult-surface bridleways close to me that rise up to the woods. On my usual bike with 25” lowest I’m down to ridiculously low cadence at various points on both paths, and daren’t stand up on the pedals because that instantly causes loss of grip, so it’s a fun test of technique, which I sometime pass and sometimes fail. I noticed that MTB riders breeze up these paths, so earlier in the year tried them on a bike with 18” bottom gear, and actually worse tyres for the job than my usual. So much easier! I didn’t actually go right to the lowest gear, but I could keep cadence high enough to remain in the reasonably efficient zone, and the steadier delivery of torque made it a lot easier to avoid loss of adhesion.

And, what Cycle Tramp says.