Those with shortened cranks

[[XAP]Bob]

More force, not more power

[531colin]

Considering how long recumbents have been around I'm surprised nobody seems to have worked it out.

If this thread is anything to go by, we may never know...

[[XAP]Bob]

Until the UCI allow them and sky decide to work out marginal gains

[NATURAL ANKLING]

Hi,
Seat backs were banned as well as anything which restricts you falling off back of saddle by UCI IIRC.
Pushing on the back of seat of a recumbent is not wasting energy but only legs can supply energy, also you cant sit up or crouch, change upper body position to affect muscle dynamics much, hip to thigh.
Isn't a recumbent faster on flat because of aerodynamics, but cannot accelerate faster from a start because only leg power is available.

Uprights climb faster because you can use upper body / core and body weight to push down harder on pedals as well as change body position, thus change muscle dynamics hip to thigh.
Has anyone done data ignoring aerodynamics on both upright and upwrong?

[nigelnightmare]

Re Shorter cranks

They help because you can't rock your hips in a recumbent as you do on a DF, So with longer 175mm cranks your knee is flexing further on a recumbent
Moving it outside the optimum power/comfort range. You end up feeling squashed and overextended with each revolution of the pedals.

Re Up Hill
DF riders are using GRAVITY when they stand up therefore they can keep up the higher output for longer as it's their weight that helps the pedals for almost 120 deg of pedal rotation.
I.E. 2 O'clock to 6 O'clock.
Also they can and do pull up no the handlebars to give even more force which is something that recumbent riders cannot do.

Recumbent riders have to rely solely on leg muscle power without the assistance of gravity/body mass and upper body strength.

Hope that makes sense

Couple of problems, really......
1) If you are rocking your hips on an upright, then your saddle is too high. Or possibly your cranks are too long and your saddle is too high.
2) The only way you can use gravity to propel yourself is by starting from the top of a hill. When out of the saddle, most people pedal by extending and flexing the knees. However, if you were to pedal by moving your body up and down, then your body moves down under the influence of gravity, but you have to lift it back up again by muscular work, so there is no net gain to be had. (I can't quite picture how that would work....on my bike, when one pedal is at the top, the other one is at the bottom..... )

Certainly on an upright, its possible to use core strength to assist pedalling....but earlier in this thread, I was told that you can generate MORE power on a 'bent by pushing against the seat than you can by working the bars on an upright. If that is the case, then 'bents should climb and accelerate faster than uprights.....which they don't seem to do.

DUH!!
1. Try riding a DF without your hips rocking at all.(Watch some videos of cyclists).

2.When you stand up on the pedals WHAT DO YOU THINK PULL YOUR BODY TOWARDS THE GROUND magic or GRAVITY?

3. More power at the pedals BUT you only have LEG muscle to provide that power and if you do use the seat to press against you'll wreck your knees.
Recumbents do accelerate faster than DF's.......

..................on the flat and downhill.

[nigelnightmare]

Re Shorter cranks

They help because you can't rock your hips in a recumbent as you do on a DF, So with longer 175mm cranks your knee is flexing further on a recumbent
Moving it outside the optimum power/comfort range. You end up feeling squashed and overextended with each revolution of the pedals.

Re Up Hill
DF riders are using GRAVITY when they stand up therefore they can keep up the higher output for longer as it's their weight that helps the pedals for almost 120 deg of pedal rotation.
I.E. 2 O'clock to 6 O'clock.
Also they can and do pull up no the handlebars to give even more force which is something that recumbent riders cannot do.

Recumbent riders have to rely solely on leg muscle power without the assistance of gravity/body mass and upper body strength.

Hope that makes sense

Couple of problems, really......
1) If you are rocking your hips on an upright, then your saddle is too high. Or possibly your cranks are too long and your saddle is too high.
2) The only way you can use gravity to propel yourself is by starting from the top of a hill. When out of the saddle, most people pedal by extending and flexing the knees. However, if you were to pedal by moving your body up and down, then your body moves down under the influence of gravity, but you have to lift it back up again by muscular work, so there is no net gain to be had. (I can't quite picture how that would work....on my bike, when one pedal is at the top, the other one is at the bottom..... )

Certainly on an upright, its possible to use core strength to assist pedalling....but earlier in this thread, I was told that you can generate MORE power on a 'bent by pushing against the seat than you can by working the bars on an upright. If that is the case, then 'bents should climb and accelerate faster than uprights.....which they don't seem to do.

DUH!!
1. Try riding a DF without your hips rocking at all.(Watch some videos of cyclists).

2.When you stand up on the pedals WHAT DO YOU THINK PULL YOUR BODY TOWARDS THE GROUND magic or GRAVITY?

3. More power at the pedals BUT you only have LEG muscle to provide that power and if you do use the seat to press against you'll wreck your knees.
Recumbents do accelerate faster than DF's.......

..................on the flat and downhill.

[531colin]

..............
DF riders are using GRAVITY when they stand up therefore they can keep up the higher output for longer as it's their weight that helps the pedals for almost 120 deg of pedal rotation.
I.E. 2 O'clock to 6 O'clock..........

OK, lets try this again. I stand on my right pedal at 2 o'clock, and let gravity take the pedal down to 6 o'clock.
Now my left pedal is at 12 o'clock, and my body is at 6 o'clock.
If i want to stand on my left pedal at 2 o'clock, I must now raise my body using my muscles....ie, no net gain.

[[XAP]Bob]

The gain is in the different contraction regime - a snap lift is folllowed by a gradual release from gravity.

Of course it's not that simple either, since you don't fully 'bob' most of the time, and you can lift the lower back and then straighten the body upwards to relieve the legs of the lifting work and engage the other muscle groups to lift the body somewhat.

It's complex, and until SKY decide to analyse the marginal gains ... were unlikely to know absolutely.

[531colin]

Until somebody posts a video, I question that most people "bob" significantly, let alone 2 cranks length worth.
when i'm out of the saddle, i'm pulling UP on the bars.
So, if I'm standing on the pedals and pulling up on the bars, where does the force ( power, whatever) that lifts my body come from, if not from my legs?
I'm not questioning that "its complex" or, that you can use "core strength, arm strength" or whatever to help on an upright...
But you categorically cannot use gravity to drive you uphill.
And now, I'm going for a ride.

[[XAP]Bob]

Don't like the guy, but this was the first link I hit on YouTube:

https://youtu.be/ThexiR98TIg

Clearly the back half of almost all of the out of seat riders is bobbing.
It's not a whole body bob, but it is a significant bob.

As none of us have the resources of sky, we're not going to get to the bottom of the question quickly...

[Geoff.D]

Back in the 90's there was a magazine called "Bike Culture Quarterly". I read an article in one edition which referred to some university research about the optimum position for delivering force to the pedal when on a df bike. It concluded that the best position was crouched forward, with the knees coming up into the chest before delivering the power stroke.

I believe it also concluded (but I may be wrong here) that this position wasn't best for getting oxygen into the lungs, thus limiting the length of time that maximum power can be exerted.

This seems to be Bourne out by how people ride. For example TdF riders do crouch forward when going uphill, and do sit up when wanting to (needing to) replenish their depleted oxygen supplies.

I've often taken this as part of my understanding as to why recumbents don't climb so well. Although we can press back on the seat, our upper body/thigh angle can't get as small as on a df in order to deliver that optimum position for delivery of force. So we can't deliver optimum power at the pedal. Whatever personal power output we might have at our disposal, delivering it at the pedal is limited by the force we can exert and the pedal speed we can cope with .

However, being able to keep out chests "open" does allow us to deliver whatever power we do have at our disposal over a longer period, with more physiological comfort.

This, of course, is a comparison of recumbent riding and df riding in the saddle. It doesn't follow the immediately preceding discussion about "bobbing" etc.

[531colin]

Don't like the guy, but this was the first link I hit on YouTube:

https://youtu.be/ThexiR98TIg

Clearly the back half of almost all of the out of seat riders is bobbing.
It's not a whole body bob, but it is a significant bob.

As none of us have the resources of sky, we're not going to get to the bottom of the question quickly...

OK, their bums are bobbing up and down.
According to Nigel, they are getting gravity assistance from pedal at 2 o'clock to pedal at 6 o'clock, on 170mm cranks thats what shall we say, 300mm (a foot in old money) worth of bobbing.
Do you reckon they are bobbing 300mm?....I reckon its more like 100mm.

2 more things.
Their knees are bent while they are bobbing, their knees are not locked out straight. So all thats stopping their knees from buckling, is muscle work. Its just as much muscular effort to support your bodyweight on a bent knee as it is to push down with a force equivalent to your bodyweight.....in fact, its the same thing.
Having bobbed down, they must then lift themselves back up again. This is either done by magic, or by muscle work.....sure as eggs is eggs, it ain't done by gravity.

On an upright, out of the saddle, you can put extra power to the pedals 2 ways
Pulling up with your cleats on the back pedal (with its equal and opposite downward force on the front pedal)
Pulling up on the handlebars so you can push the pedal down with more force than your bodyweight. But there is a snag here as well, because you have to expend that energy twice.....once pulling up on the bars, and again preventing your knee buckling.....because if you are pushing the pedal down with a force equivalent to your bodyweight and you then pull on the bars as well, your knee is going to buckle unless you do something about it.

[[XAP]Bob]

I suspect (from experience) that the bobbing does some 'averaging' of the power delivery that can't be done on a bent.

But until someone does a rigorous analysis we aren't going to get there by guessing...

The most rigorous tests we have were nearly a century ago, when the bents won road races...
Given that Amanda Coker is basically runnning to a power meter it would be interesting to know what speed a highracer would achieve for the same input - completely ignores any question of hills of course

[531colin]

Looking again at the vid. you linked, many riders are rocking their pelvis, a few bob up and down noticeably.
It could be thats just the way your body works; the foot you are pulling up on, that side of your pelvis raises, the foot you are pushing down, that side of your pelvis drops.

[nigelnightmare]

Looking again at the vid. you linked, many riders are rocking their pelvis, a few bob up and down noticeably.
It could be thats just the way your body works; the foot you are pulling up on, that side of your pelvis raises, the foot you are pushing down, that side of your pelvis drops.

AHH!
The penny finally drops.

When sitting in a recumbent you are sitting on your bum and the pelvis cannot rock from side to side,

Therefore you will require shorter cranks or you will be over flexing/extending your knees & ankles.