;)

Steel is a fantastic material for springs. Ti... I doubt it has as small of hysteresis, but I have no data to back that up.

Like everyone else, in this case.

Yeah, could be. I know that Ti can deflect further before fatigue starts to build up, and I was assuming that would mean less heat generated, but maybe not.

speed wobble
 

Almost every bike has a point where it can have a speed wobble. I have read a bunch of tech junk on the issue because a friend of mine on my old litespeed vortex has that problem. It can be weight distribution, fork angle, wind in spokes, etc. It could even have been as simple as your number. Clothing can pick up turbulence and hurt you.
The science says that a bike that weighs almost nothing with a rider on top of it riding on two patches of rubber 1/2" by 1" at speed on a surface that is not perfectly smooth can get out of straight line motion pretty easily. Even undulations in blacktop can cause it. Sounds like you used the best method to stop it.

If my frame has been stiff for more than 4 hours, should i call my doctor?

If you are stressing your frame laterally when you pedal, isn't the frame absorbing the same force whether it deflects a lot or a little? The rider is "wasting" the same amount of energy by exerting force laterally whether it results in noticable flex or not.

^^^
No.

F = k*x where F is force, k is the spring constant, and x is the deflection.

At your age you should just have more sex.

I find stiffer frames much more comfortable to ride and much more satisfying. But until someone does some proper scientific tests, I don't think we'll ever know the answer to this particular question...

very simple.
any energy wasted on frame flex is wasted energy that could otherwise be translated to the ground for acceleration.
same reason drag cars use subframe connectors to stiffen the frame and reduce flexation. all the energy used to twist the frame is energy not making it to the street.

You've clearly not done your reading (above) ;). In a dragster, the initial frame flex will be returned to the system as the torque lets up. It turns out that only happens on the other side of the finish line (because the engine keeps the power going), so you don't want to take that hit in the beginning knowing you won't get it back until the race is over. Plus, there are serious handling and traction concerns with a twisted dragster.

On a bicycle, the frame flex is returned to the system with each pedal stroke. If you can't visualize this mechanism, read the pages above. It's covered about twice on each page I think. So, you spend some energy winding up the frame during the power portion of the stroke, and the frame gives it back to the drive train as your power subsides on the dead portion of the stroke -- this happens continuously, not all at once, as the pedal force declines.

Regardless of whether the frame flex is returned to the system, isn't the same amount of rider energy being exerted laterally (and therefore not contributing to forward movement) whether the frame flexes or not? I'm no physicist, but exerting 10 psi on a steel beam vs. a pendulum is still 10 psi regardless of the reaction. The force the cyclist exerts in the wrong direction is really the issue, and that to me would be a constant. Whether that inefficiency causes flex or not doesn't change the extent it exists.

Have you ever noticed on a steep hill that if you start mashing, you get into this cycle of lunging forward with each downstroke, then gravity takes it back before the next downstroke starts, then another lunge, another deceleration, and so on. Really inefficient and a lot of energy wasted.

So.... I'm wondering if a frame with a healthy amount of flex would end up smoothing out the power transmission? The frame flex becomes the mechanical equivalent of a capacitor, limiting peak power transfer to the wheel while distributing the total energy output across a wider range of the pedal stroke.

Following that line of thought, instead of the conventional wisdom of a stiffer frame being better for climbing, a flexy frame would be better for climbing, since you waste less energy on unsustainable acceleration that is immediately given up to gravity.

Yeah, that's certainly one of the theories. Makes sense to me, but again, no data. Surges are bad, and since a stiffer frame is more responsive, it's going to surge more...

A lot of the reviews for the original Slingshot bikes supported this... (they were said to to be exceptional out of corners in crits)

You're way off base here. You're using something that you don't have the slightest idea about as some sort of proof by example.

The energy of a closed system cannot be created or destroyed. So let's assume we are in a vacuum and riding our bike. We have what amounts to chemically stored energy in our muscles. When we push on the cranks, it produces kinetic energy and heat energy. The kinetic energy pushes us forward. The heat energy is a waste product of the power transmission from the pedals. The chain, bearings, tires, etc. all take miniscule little bits of energy.

The question is whether or not frame deflection creates heat. Take a paper clip, bend it back and forth for a little while and the feel the flex point, it'll be warm. Take the spring out of a ball-point pen, and flex it between you fingers for a while, does it get warm? No. Why the difference? Are our bikes more like the paper clip or the spring?

The materials that we are working with are being subjected to stresses which are below the yield strength (i.e. at a level of stress (or flex) that doesn't permanently deform it). Heat is produced when we permanently deform the material. We never permanently deform a frame with a pedal stroke therefore, heat is not produced. If we aren't producing waste heat in the frame itself, then frame stiffness does not effect power transmission.

The one caveat to this would be if the frame deflected enough that it screwed up the chainline and in doing so reduced the efficiency of the chain drive. This is not a reasonable situation on anything even resembling a modern road bike.

Street cars that are converted to dragsters use subframe connectors because they put big enough engines and big enough tires on the car that it can literally destroy itself. A unibody car (all street cars) is sheet steel and spot welds. It just cannot take the huge loads that are put to it. It's not easy to rip one of these cars in 1/2. It has _nothing_ to do with power transmission loss.

Top Fuel dragsters, the fastest of the fast, have frames that deflect massively. Some tubes in the chassis will actually be slip fit to facility greater deflection. Of course, they're only working with 7,000 HP or so and running 335 mph. They probably don't know as much as a bike guy.

Chassis deflection is something that racecar engineers are concerned about, but it has nothing to do with power transmission. They change springs a lot of racecars, and particularly on the rear of the car, a soft rear spring _helps_ accleration by giving the tires better traction.

Hysteresis in a spring? Are you serious? Does not exist to any extent we can measure. The only hysteresis you get is by the twisting of the end coils, and that is not material dependent.

People use Ti springs. Color them very, very rich.

Maybe I'm oversimplifying things here, but couldn't farme flew be compared to a mtb with rear suspension that bobs while pedaling? That definitely hurts efficiency. Plus, would the frequency of flex returning to the system equal that of pedaling or would they be out of sync & therefore working against smooth power transmission?

Either way, I find the crisp response of a stiff frame very satisfying and that alone would make it worth pursuing for me.

No, read the thread. I think this is on the 1st or 2nd page. (:lol: "farme flew" )

Yep, that's where they make sense. If you prefer the feel (most seem to).

My farme has lots of flew. Perhaps becuase of my masive guads.

If your farme doesn't have enough flew, perhaps you can use a catapult. That'll make it flew.

Aren't due for some WRI or something? ;)

Nope. Club's time-trial tomorrow. Yesterday was complete rest, today is half-workout day.

You think this is bad - by tomorrow afternoon I'll be bouncing off the walls.

http://kirkframeworks.com/Flex.htm

Here is the opinion of a respected custom frame builder. Read the section on Bottom Bracket/Drivetrain flex. I see no reason to disagree with him.

Sweet, good luck in the TT.

Well, he mentions that a flexy frame may not return to the neutral position before the next pedal stroke starts. Any frame with that low of a vibration frequency would be unrideable, and probably made of coat hangers :)