Another (but different!) crank length question

General
1

I thought every crank question had already been asked, but I can’t find anything on this specific one!

How does crank length affect calorie burning? We’ll say it’s an identical route for easy comparison and because I imagine most people stick to the same regular/local rides for most of the time.

Will shorter cranks burn fewer calories since you go faster (taking less time to complete the ride)? Will it be the same since (assuming wheel and tyre are the same) it’s the same number of revolutions for a given distance? Or will you actually use more calories since you use more force/muscle power on the shorter lever length?

My feeling so far is it will be pretty much negligible difference but if anyone knows better I’d be interested to know!

1 Like
2

My feeling is the same as yours - the difference shouldn‘t be dramatic. That said, I tend to think that you‘re likely gonna burn a few more calories with shorter cranks, since you‘re likely gonna ride faster, thus spending more energy to fight the airflow.
But that‘s only speculation.

3

That’s funny, I would have say the opposite: with shorter cranks, you have to spend less energy to ride at the same speed as with longer cranks.
However, if you ride uphill, you’ll spend more energy with shorter cranks as you’ll have to push harder to keep rolling.
So, there is probably no definite answer: it all depends on how you ride.

4 Likes
4

I agree that the difference is likely to be negligible. However, I think that longer cranks may cause one to burn more calories. While shorter cranks do seem to be faster, they also seem to require less effort while the unicycle is at speed/coasting. Longer cranks, on the other hand, require much more movement in the largest muscles in your body - your legs.

I guess a good indicator would be, which one makes you sweat more over time/distance?

My 24” Koxx Track Monster with 160mm cranks seems to make me sweat more than my 24” Koxx White Russian with 130mm cranks, if I complete the same 2.5 circuit/route.

The unicycles are essentially the same, except for tires and cranks. The Track Monster has a Duro 24x3 knobby tire, and the White Russian has a CST Cyclops 24x2.6 tire, with less rolling resistance. While I had hoped to add some clarity with the comparison of the two unicycles, the tire difference may have just muddied the water again. :grin:

1 Like
5

I thought Calorie counting was a girl thing.

2 Likes
6

probably has something to do with the type. I ride 95% of the time with a 125mm crank length. Most of the time it’s on easy-to-ride dirt roads, forest paths, no trails. Sometimes there are 10% inclines. It doesn’t matter if it’s a 26er, Fatty or 27.5er. I always do it with 125mm. I only really use 145mm off-road or in the mountains, which is very rare. On my “home ride” I’m much more efficient, faster and more relaxed with 125mm than with 145mm. With 145mm I would need more time for it and it feels more strenuous. So I would probably burn more calories.

7

My first unicycle was a Club 26er road uni that came with 150mm cranks. I rode with those cranks for a pretty long time until I started playing around with different crank lengths. I started riding 125s for a while, and when I switched back to 150s I thought to myself “how did I ride so long with these?” :sweat_smile:

I feel like going longer will start increasing calorie count, though more towards the extreme end of things. Moving from 100mm to 125s probably wouldn’t make as much of a difference as 125s to 150s in my case.

1 Like
8

I also feel the same. But with 150 mm Cranks i can’t go uphill because the ctankd are too long but with 127mm is a good length for going up the hill.

1 Like
9

I would say that it is most of the time pretty close.

When you are going forward at a sustain speed, you basically have three things to fight :

  • The rolling resistance of your tyre.
  • The aero resistance.
  • The incline resistance.

None of those is linked to the crank length, so you basically need to put the same amount of power with any crank choice.

When pedaling, the amount of power that goes to the wheel is :

  • P = F.S (P : Power in Watt, F : Force on the pedal in Newton, S : Speed of the pedal in meter/second)

The speed of your foot (or the pedal) is :

  • S = L.2.π.c (S : pedal speed in meter/second, L : crank length in meter, c : cadence in /second)

As said previously, at any given speed, P is constant for any crank choice, as is c, we then get :

  • P = F.S = F.L.2.π.c <=> F = P/S = P/L/2.π/c = P/(2.π.c)/L

Since P/(2.π.c) is not linked to the crank length, to use shorter cranks, you will have to put more force on your feet, but they will go slower, so in term of calorie, there should be basically no difference at rather slow speeds. You might damage more muscle fibers with shorter cranks, which might cause more aches afterwards.

However, at higher speeds, there is one thing that will accelerate with every pedal thrust : your legs. If you do a bigger circle with your feet, your legs will move more, and accelerate faster. And that is also power consumption. This means that at higher speeds, using longer cranks will consume more calorie.

What I just said, is only valid in a perfect world. In the real world, there are perturbations, which will lead you to get imbalances you will have to correct. Those will take longer to correct on shorter cranks, which means more calories consumed (calorie = power x time). So shorter cranks, especially if not perfectly mastered or at lower speeds will consume more calories.

So in the end, shorter cranks should consume less energy than long cranks at high speeds, and longer cranks are better at low speeds or when going uphill or on uneven terrains.
Short cranks will also cause more muscle fiber destruction which means more aches afterward, especially at low speeds or when going uphill.

4 Likes
10

I don’t think all factors were taken into account in the calculations. The knees are bent more with long cranks. This fact alone is more strenuous. In addition, with horizontal cranks the pedals are further forward, so the power is applied differently (I’m not a physicist). You would have to add an “efficiency factor”. This is not the same for everyone. People with short legs have more trouble with long cranks than others with long legs. Shorter cranks encourage a rounder pedal stroke and less wobbling. I suspect that if you included leg length and knee angle as a factor, you would get different results depending on the size of the person.

2 Likes
11

Both short and long cranks have their own specific technical features.
Long cranks are often associated with beginners. In fact, after a little practice, you realize that many things become easier when using shorter cranks. Progress is easier than mastering long cranks, which require greater coordination. Every mistake is punished more severely because of the greater lever arm.

That said, for the same speed (= same power), in the situation where you’re far from your power limits and there’s no need to accelerate, it will always be more economical to use short cranks, even if you pedal very efficiently with long cranks.

But if the aim is to exercise, there may be an advantage in expending more energy (and therefore using long cranks).

2 Likes
12

Another point to add to the debate, what about the same crank length but a bigger wheel? I have to assume it will burn fewer calories given that it will be both fewer revolutions for a given distance, and less time but at the moment (to be fair I have only done 3 rides!) it feels like I’m using more energy on my new Oracle 27.5 with 150 cranks than I was with the 24 which also has 150’s. However I imagine it will become more comfortable/less effort as I get used to the bigger wheel.

For context my regular evening ride is 6.3 miles with 200 feet elevation, on my 24 it took around 57 minutes (average around 6.4mph) and on the new 27.5 it took 50 minutes for the same route (average 7.4mph).

13

Are we trying to measure

Calories burned per hour

OR

Calories burned per Mile/Kilometer?

1 Like
14

I suppose per unit of distance, given that I tend to stick to the same routes. I have 2 regular evening routes, one is 6.3 miles with 200 feet elevation, the other is 5.9 miles but has almost 300 feet elevation. Each takes around an hour on the 24 with 150mm cranks, a little less now I have the 27.5. I want to keep improving my fitness and losing weight over the winter to be better on more challenging rides when (hopefully!) the better weather and lighter evenings arrive in spring.

I’m just curious what difference crank length and/or wheel size changes will make since I am actively trying to lose weight. And I know diet has a bigger impact than exercise, I have made changes in that respect too!

15

I would say that in the perfect physics world, with no loss of energy due to imbalance, any size of wheel or cranks should end up with the same energy consumption. However, pedaling fast especially on longer cranks is more energy consuming due to the consumption of just moving your legs (and more imbalances created by any unperfect feet movement).

If your goal is to lose weight and get fitter, the most important thing is IMO to have fun while riding. This way, you will want to ride more often and for longer, which leads to a way bigger energy consumption and body adaptation (= getting fitter). So maybe don’t search for the most energy consuming way of moving, but for the funniest (which can be running, biking, unicycling, muniing, skiing, etc…)

4 Likes
16

I’d need to review it again, but from what I remember, there were some studies for which gear to choose in cycling and they found a relatively large range where it did not really change power requirements for a given speed. I’d expect something similar for crank lengths and unicycling, maybe that range is slightly smaller.

However, as a practical tip, I would rather look at adding a bit of varying intensity into your rides to burn more calories than your setup. Maybe on some rides, really try to ride the uphills as fast as possible to get a more intense workout. I don’t really use unicycling as aerobic training, but for running some fast intervals once in a while make it more entertaining for me, while providing good training. (Our body is less efficient at high intensity, so you’ll tend to burn more calories too)

17

Absolutely. I lost about 11kg just by quitting eating (and drinking!) refined sugar. Went from slight overweight to normal weight, according to the body mass index. As a side effect of this diet I started to eat more fruits and vegetables, which certainly helped. As soon as I lost some weight the desire to move my body increased, which is one part of what brought me back into unicycling on a regular basis.

I stated earlier that I think shorter cranks should end up in burning more calories because you‘ll typically ride at higher speeds, thus needing more energy to overcome the airflow. I seem to be quite alone with this opinion and am not so sure about it anymore. The increase in speed is unlikely to be dramatic, so the effect will be small. Probably smaller than the effect of the less efficient pedaling that the longer cranks undoubtedly implicate.

1 Like
18

If there is a lot of acceleration involved I think you spend less energy with longer cranks (lower gain ratio) and if you cruise at higher speed you spend less energy with shorter cranks.

When trying to ride fast on 150 mm cranks now I just feel that I fight the wobbly wheel and my legs are just thrashing around. And when riding on 100 og 89 mm the lack of effort of maintaining the speed actually tricks me into thinking I am riding slower than I actually am.

This guy I know rode 100 km his 36" with 114 mm cranks and a months later or so he rode a whooping 140 km on 75 mm cranks. When I asked he said the 140 km on 75 mm cranks was actually less fatiguing. Well, physically at least. :sweat_smile:

And I absolutely agree. Have tons of fun while riding and you spend way more time on the wheel! This is the absolute way to go in any case! :star_struck:

19

I agree with you, but the energy spent in just controling the wheel at high speeds with long cranks is IMO more important than the effect of the air resistance. Also, I can certify that with short cranks you can get to speeds at which airflow really starts to be noticeable (i.e. I used to be able to reach speeds up to 30 kph on my 29/75).

1 Like
20

Alternatively, you could use torque concept to come to the same conclusions.