Except that this time we have data and a consistent, simple explanation for the observed effect.
That’s a misinterpretation of the data and of Peak Torque’s video. His whole point is that you measure downstream from the suspension and your body has to work harder so that 300 W reach the power meter.
That’s like measuring your power with an indoor trainer or hub-based power meter: drive train losses are priced in. So if you wanted to compare the efficiency of a clean vs. dirty drivetrain with this setup, you will get a zero result.
I am referring to all of the data presented, not just PT’s. I’ll go back and watch both videos again, but my recollection was that the higher HR runs were primarily associated with the standing runs…at least with Dylan.
Perhaps part of the issue is how power meters measure power?
To my knowledge, they basically use average torque multiplied by average angular velocity (RPMs) measured several times per revolution but typically recorded at intervals of once per second.
Given the way that suspensions work, I wonder if it doesn’t take higher peak torques (more effort) to achieve the same average torque and therefore the same measured power.
We know that times are basically identically with identical measured power, so measured power more or less equals output at the wheels, but we also know that energy IS being lost to heat, because physics.
We just don’t know how much, or whether it it’s significant. It certainly feels significant, especially when riding hard while standing up, which makes the suspension stroke the most.
(Sidenote: This discussion ignores the fact that pedals aren’t the only way in which effort can be (usefully or not) input into a bike suspension… but you shouldn’t really be riding with so much weight on the handlebars or saddle anyway.)
Race cars, shy of top fuel dragsters and funny cars, ALL HAVE SUSPENSION. And those crazy aformentioned cars have massive tires that deform massively at launch, effectively behaving as suspension.
Warning, bold and dangerous statement follows. I think cyclysts are wrong (I said it). Suspension, makes bikes faster. If a road bike without suspension, weighed the same, and was as aerodynamic, as a road bike without suspension, shy of UCI and race organizers banning it, racers would use it, and be faster. It saves energy, including metabolic costs. Just like tires, different conditions warrant different suspension types and travel amounts. But zero is probably never ideal, all other variables being equal.
Now, can a scientist on the forum design an experiment, and call for volunteers? Count me in.
I don’t think cyclists are wrong, because you seem to think that a locked out bike has no suspension. It does. When you lock out a 100–120 mm fork, you still have 20–30 mm of travel. The precise number depends on various parameters, not least the amount of sag you have set. Ditto for the rear, although precise numbers are harder to come by. Still, on most terrain (starting from smooth tarmac) you’ll be faster locked out.
That is why Peak Torque did his experiments on tarmac: on smooth tarmac you are not limited by tire grip, i. e. save for rolling resistance, all of the energy you put into the rear wheel is used to propel you forward. On bumpy terrain that need not be true. Indeed, on most terrains and in most circumstances a modern fully is faster than a hard tail, even if you pay a weight penalty. Modern XC and downcountry fullies are very good at resisting pedal bob, although this is less true the more travel you have since you optimize your suspension for different things.
Can you prove it? It sounds like an excellent null hypothesis …In all seriousness, I want to know one way or the other, before stripping my bike of its lockout cables and levers, because it might weigh 30 or 40 grams, and looks undesirable. I have quite the rats nest off the front of my bike.
Have a look at what XC pros are doing: nowadays they are using fullys for most races. They are using their lockouts constantly.
And when you go longer, comfort/fatigue becomes a factor, too. Of course, I am not referring to leg fatigue, but fatigue in the arms and in the core, which is a separate issue.
I get what you are saying about power and energy. That isn’t really what I am arguing.
I am curious if that energy we are talking about, the one that is being converted to heat in the shock/fork would otherwise turn the cranks. My gut feeling says locked out is more efficient too, but I find that lately a lot of the conventional wisdom as it relates to cycling, have been false:
flat pedals versus clipless: Actually not more efficient
crank lengths
skinny tires
high pressure in tires
and so on
I think this would be an interesting, low tech test, that could offer some insight:
Put a rigid bike onto a trainer. Place a scale under the front wheel. Place a scale under the trainer.
See if the weight (contact force) changes as a cyclist is cycling.
If it does change, that should imply force/energy is being “wasted”, and would have compressed the suspension.
Does it even matter where it would go? It’s extra energy that has to come from you. So the less energy going into the shock to be converted into heat the less energy output you’re having to do.
But it would go into propulsion. What causes pedal bob? Pedaling. Energy is coming from your legs into the cranks and is reacted into the frame on the way to the wheels. When there is a spring-damper in the frame then energy gets absorbed into the damper. I guarantee companies like Spesh have a physics model of a FS bike so they can calculate the exact energy flow. Why do you think they still put Brain shocks on their race bike? It’s literally a physics calculation to get the energy that goes into the shock. Inputs are sprung mass, damping ratio, spring rate, etc.
??? Then why did you ask if it mattered where it would go?
But not all of a rider’s energy is transferred into propulsion.
Speaking from personal experience, yes they do…but as noted above, there are a LOT of forces which need to be balanced when developing a FS bike. It is extremely complicated and is not all about pedal-induced forces.
The Brain shock does a lot more than just lock out suspension when climbing…it is constantly altering shock performance according to the terrain.
Of course it matters where it goes, and where it comes from. That is the entire point.
That’s why I think the “scale experiment” could shed some light.
I have an enduro bike with plush coil suspension & a high starting leverage ratio. I can see the shock moving, albeit not much, by me simply resting my hand on the seat. This while the bike is stationary, no rider on it. The slightest shift in my mass’ center of gravity when I am sitting on it, not pedaling, leads to movement at the suspension. So again, just because suspension is moving, does not mean that the force/energy that caused it, would otherwise drive the cranks.
Yes, but here the explanations for these points was much more subtle and sketchy — and ultimately not (universally) correct.
A simple energy balance argument is as easy and direct as it gets, and is bullet proof. You could measure the heat dissipated by the shocks in both setups. That’d be energy in addition to what you measure at the cranks. The only way the efficiency were similar is if you can show that in the closed position the energy dissipated in the shocks will be dissipated elsewhere in addition. A gas exchange experiment could also accurately measure the total energy produced by your body.
That experiment would give no relevant data, because it is not about force, but about energy = power over time = force parallel to direction of travel times distance. So if you want to measure forces, you must measure the share of the force vector, which is parallel to the direction of travel. Pushing very hard on a wall costs no energy(*).
(*) It does cost human muscles energy to push on immovable objects, because of the way they work. But mollusks and other animals with different types of muscles can do that at no energy expense to themselves.
A suspension consists of two parts, a spring and a damper. A spring stores energy (in practice very little energy is lost due to friction). But a damper is designed to dissipate energy into heat, this is literally its job. That is energy lost to propulsion. You can literally measure the change in temperature with your hand (if you have been using your shocks for long and vigorously enough).
I understand how a damper works, and I also have a basic understanding of physics from my master’s in structural engineering. I am merely pointing out, that the force that is compressing the suspension, may not otherwise contribute to rotation of the cranks.
Just like I said before, on a bike with high leverage ratio, and high end suspension like my own, the slightest movement in the lateral or vertical plane by the rider causes movement of the suspension.
If you replace your “wall” with the contact to the ground by the wheels. No work is done here on a rigid bike, except deformation of the various components. if you add suspension the “wall” would move, and work is done. But that doesn’t mean that this work would otherwise go through the cranks. Unless that inventor of the “energy recovery” wheel is on to something
This would actually be relatively easy to test. Starting from a standstill with your front brake partially applied, try stomping on a level with the suspension alternatively locked and unlocked. See if having the suspension locked or unlocked changes how much force on the pedals affects is needed to make the bike move forward.
…In all seriousness, I want to know one way or the other, before stripping my bike of its lockout cables and levers, because it might weigh 30 or 40 grams, and looks undesirable. I have quite the rats nest off the front of my bike.
