Planing

[Mark Kelly]

Sorry the asterisk next to the spring constant number was meant to indicate a footnote which I didn't insert.

You can work out the spring constant in your achille's tendon by bouncing in place on an unsprung floor and working out your natural "pogo" frequency.

2 . pi . F = Sqrt (k/m) where k is the spring constant and m is the mass: in this case the mass is half your bodyweight since you are bouncing on both legs.

If you try bouncing on one leg the frequency should reduce by a factor of 1.4.

[waterlaz]

At what point is the force that causes the deflection removed?

There is no "point". The force gradually changes in direction and value. While this happens some parts of the frame return energy while others may store it.
Nevertheless, the energy is not wasted and it does move the bike forward.

[jclay]

And yes, there's some fore/aft strain energy stored in the SSs & brake arch which contributed to wheel rotation and which wouldn't exist on the road.

My statement, above, is incorrect. The energy stored in the SSs & brake arch would not, upon release of the brake lever, contribute to wheel rotation. If anything, it would retard it. I pay you guys to check my logic and catch my errors!!!

Mark: Is the Achilles tendon stretch in your model counterbalanced by any driveline element, say the chain?

[Eric Estlund]

[WFSTEKL]

In 1983 I purchased a Colnago Superissimo. It was an Columbus SL tubed frameset in Almost Gios Blue. It was also my first Italian road racing machine. I tossed a Campag. NR group on it that I mined from my previous rig, a Univega with no pedigree. I was in love. I competed on it a bunch, including my first District TT that I pounded out in less than 60 minutes. In those days TT wheels were 32 hole GL330s, and I sat like a brick on that machine. My infatuation with that machine began to wane when it began to display some unnecessary defiance. For example, when I leaned on the pedals it always ghost-shifted......shit. When I sat up to peel off a sodden jacket, it shimmied. I hated that dammed frame!

I decided to invest in a NASA inspired aluminum road rocket. This new machine was the ticket. I stomped on that thing until my legs became powder. I rode it up mountains, along the train tracks, and even at Nationals. One late fall day it was damp and cold. Then rain drops began to chase rain drops. I decided to pull the old Colnago off the peg for my daily ride rather than risk having the NASA bike catch a cold. I reluctantly pedaled my Blue Bag of Bones off to the grey. When my legs awoke, I began stomping on it, mostly in an effort to break it so that I wouldn't have to look at it again. That old horse flew! I mean took flight. The BB swayed, the top tube groaned, but it shot forward, and all I could do was hang on. Was I planning? Hummmm.......don't know, but I was in love again.


William Steckl

[happycampyer]

So, now in addition to height, inseam, sleeve length, shoe size, favorite color, etc., custom framebuilders should also ask for the spring constant of the customer’s achilles’ tendon.

William Threadgill

[WFSTEKL]

So, now in addition to height, inseam, sleeve length, shoe size, favorite color, etc., custom framebuilders should also ask for the spring constant of the customer’s achilles’ tendon.

They would be remiss not to ask.

William Steckl

[thollandpe]

You can work out the spring constant in your achille's tendon by bouncing in place on an unsprung floor and working out your natural "pogo" frequency.

So, now in addition to height, inseam, sleeve length, shoe size, favorite color, etc., custom framebuilders should also ask for the spring constant of the customer’s achilles’ tendon.

They would be remiss not to ask.

My natural Pogo frequency is to say "We have met the enemy and he is us" at least once a year.

[progetto]

You poor bastards must be having a hell of a winter up there.

[zetroc]

My bike planes, I think. Probably most do if you ride them long enough to learn how they react.

It was 82 degrees in San Jose on Saturday so I can only imagine.

[jclay]

There is no "point". The force gradually changes in direction and value. While this happens some parts of the frame return energy while others may store it.
Nevertheless, the energy is not wasted and it does move the bike forward.

Thanks for pointing that out explicitly.

[Too Tall]

You poor bastards must be having a hell of a winter up there.

You got that right.

If Mark Kelly wasn't so smart I'd feel better about saying I'm prepared to make fun of anyone who takes this seriously except for Jan Heine who is paid to take this seriously.

[David Tollefson]

There is no "point". The force gradually changes in direction and value. While this happens some parts of the frame return energy while others may store it.
Nevertheless, the energy is not wasted and it does move the bike forward.

My contention is that it's a zero sum, as what it supposedly "returns" on the one pedal stroke, it does so at the expense of the next.

[Mark Kelly]

I'd feel better about saying I'm prepared to make fun of anyone who takes this seriously except for Jan Heine who is paid to take this seriously.

For the record, I have never experienced "planing" and I doubt that it exists.

I do, however, find it annoying when people say it can't exist as if they understand everything there is to know about how bicycles actually work.

I don't know that and moreover I don't know anybody who does (I've never met Jim Papadopoulos).

[Mark Kelly]

So, now in addition to height, inseam, sleeve length, shoe size, favorite color, etc., custom framebuilders should also ask for the spring constant of the customer’s achilles’ tendon.

No, I just get people to do the pogo test and report the result, I then calculate their k factor myself.

[waterlaz]

My contention is that it's a zero sum, as what it supposedly "returns" on the one pedal stroke, it does so at the expense of the next.

Yes. But that is obvious due to energy conservation.

[Too Tall]

Yes. But that is obvious due to energy conservation.

Aaaaand we are back to my point which is how the rider adapts to or decides to deal with it. There is a head game involved which is in part why this is impossible to quantify.

Like I tell my dog when he sniffs a plate of soon to be my dinner LEAVE IT.

Well designed bikes work magnificently for 99.9999999% of the world. For the unsettled among us who seek a higher plane there is speculation. Go nuts.

[tbonefitz]

Hi guys. Fascinating read so far. As always, I know that the folks here at the salon will treat just about any topic without a reduction to ad-hominem attacks.

I agree with Josh. Riders adapt to what they have to work with. That being said . . .

I had two bikes (still have them), a steel framed Japanese Bridgestone (not an RB-1, but a racing hydroformed steel bridgestone) and an early 2000's aluminum wonderbike as rode by the pros that year. I always knew they felt different. Last year, I got a titanium super custom. First couple rides on it were weird--it seemed harder to pedal. But it was so much more comfortable than the other two, being custom, that I didn't care too much, and I rode. Now, the other bikes feel weird--and slower.

Ever since the first time I heard of the planing theory, I've always thought that there's one assumption in the whole system that is a problem--namely, that the leg itself won't absorb the spring force of the frame, if it exists. As force is applied in the very non-linear and inconsistent manner that pedaling happens to the pedals, the bike is fighting the pedals--opposite forces and all. The net positive force is propulsion. If the bike is trying to unwind itself, the cyclist would have to overpower that force or the leg muscle would just absorb some of it, right? Say it is 10 watts. That 10 watts that is added to the system a fraction of a second before will now try to fight back directly on the easiest target. That 10 watts working against the cyclist feels the same as the same 10 watts of the resistance of a crappy tire, or the 10 watts of sitting up in the wind. As i see it, that 10 watts has to go to either the back wheel or the leg muscle itself--and the leg muscle seems like the likely candidate, especially as the crank comes to the bottom of the power stroke in the dead zone, and at that point, there functionally is zero power

The next assumption is the time frame of the force. Springs return their energy as soon as they can. A spring can't store energy indefinitely. So, as I see it, as soon as the force required to add that energy into twisting the frame is reduced, even just a little, the frame unloads the equal amount of energy into the system. In other words, the frame can be unloading a watt at at time back into the cyclists legs.

Considering these two points, and Jan's assertion that stiffer frames hurt his legs more, maybe the real issue is that the returning force from the bike doesn't go into the back wheel at all, but into the leg, and we get used to the way a bike pushes back on us. So, when we're on bikes that feel like our current bike, we feel (and are) faster because the rate at which this stored power is trying to attack our legs is what we're used to, and our legs mete out power in the right amount to work with our equipment. When on a stiffer bike, the force is returned at a quicker rate, and it is more tiring to fight it. But with time, we'll get used to the spring rate of the stiffer bike, and less stiff bikes will feel "noodly" - and slower.

And with that, I further muddy the waters of this ridiculous thread.

[Too Tall]

Good read Tbone the visual is pretty well what I'm saying. In addition to leg muscles include core, arms, back etc. because we work that way when dealing with these (real) forces.

Anywho, riding bikes is less expensive than psychotherapy.

[Mark Kelly]

Anywho, riding bikes is less expensive than psychotherapy.

Amen.


Believe it or not, amen is basically Hebrew for "ain't that the truth"