Hi All

[Chalo]

Time for you to ditch the magical thinking and admit that the function of dampers is to throw kinetic energy away.

 

[full-throttle]

Time for you to ditch the magical thinking

I believe you misspelled logical :wink:

 

[full-throttle]

Consider this: With a low frequency ripple in pavement, an unsuspended bike will treat the surface as a series of small hills, decelerating on the uphill side and regaining the lost speed on the downhill side of each undulation. But suspension compresses on the uphill side, converting kinetic energy into heat in the dampers, then extends on the downhill side, again converting kinetic energy into heat in the rebound dampers, and then as the vehicle returns to its normal amount of sag, it will burn off a little more energy yet.

You forgot the spring, genius.

On each 'uphill' the energy is stored in the spring and subsequently released on the 'downhill'. The damper only controls the motion - stops the spring from oscillating. The energy wasted as heat is negligible.

Now the difference is: the unsuspended bike and rider has to follow the contour of each of these 'hills' while in the case with suspension only the unsprung mass has to follow. The rider and most of the bike travels straight.

Motion in a straight line requires less energy.

Still want to argue?

 

[Chalo]

Now the difference is: the unsuspended bike and rider has to follow the contour of each of these 'hills' while in the case with suspension only the unsprung mass has to follow. The rider and most of the bike travels straight.

Motion in a straight line requires less energy.

Again with the mistaken notions. The suspended rider moves, but more gradually. He rises less than the unsuspended rider, but then falls back down farther, and then rises up again to the static sag position. Those three movements are resisted by the suspension dampers, taking kinetic energy out of the system that can only come from one source-- the rider's and bike's forward motion.

Tell me clearly: Are you saying that dampers don't dissipate kinetic energy as heat? Or are you saying that the energy they dissipate comes from somewhere other than the vehicle's mass times its velocity?

 

[full-throttle]

I'm saying the amount is minuscule. You are the one saying is "a lot"

When surfaces are good and smooth, mechanical suspension throws away a lot of energy that could be used to propel the bike, or to keep it rolling

Now either prove that is "a lot" or shut the frock up!

Go to a local DH race and see what temperature the shocks get to after the run.

 

[Samd]

Correct. Rolling friction pales in energy consumption to drag. The oscillation is a tiny portion of the rolling friction. Now multiply these two facts->>> Do you need a pie-chart or visual Chalo?

 

[Chalo]

What is "negligible" at 5000W or more may not be negligible at less than one-tenth that much power. Aero drag (force, not work) scales as the square of speed, and tire rolling resistance scales linearly with speed, but suspension pumping losses are not directly related to speed-- the slower and more efficient your vehicle, the bigger a bite they take.

Racing road bikes have regulated minimum weights that would allow them to have suspension and still weigh the minimum. None-- as in zero-- of them have any mechanical suspension at all. It's not for lack of budget, or because guys racing 120 miles a day at fill tilt couldn't use some extra comfort. Manufacturer sponsors would love it, because it would allow them to sell a bunch of really expensive toys to eager tools. Suspension road racing bikes don't exist because they would lose. And that's at e-bike speeds or more.

When I say suspension wastes "a lot" of energy, I mean it slows me down observably more than underinflated utility tires, a heavy load of cargo, a sidewall generator, or other such things that many riders avoid because they're draggy. We can argue about whether that arbitrarily qualifies as "a lot", but it is significant, which by definition is the opposite of negligible.

On a "good and smooth" surface it wastes a lot of pedal work. On an undulating surface it wastes a lot of forward velocity and pedal work. (For my above described value of a lot.) If you have power to burn, then no big deal. But excess power comes with extra weight, expense, complexity, etc., that are inimical to a bicycle's basic virtues.

As Antoine de Saint-Exupery put it: "Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away."

You want some cup holders and a rear wing for your bike too? You know, because you can.

 

[John in CR]

I'm no cyclist, but I can definitely feel a suspended pedal bike suck up leg power requiring more effort than a bike with no suspension, same tires and road. The first time riding one I stopped to get air thinking the tires must be low on air, but they weren't.

Interesting about the road race bikes. I thought they all had the lightest construction bikes possible...part of the science of the sport.

 

[full-throttle]

Don't walk away from the answer with all this irrelevant BS

On a "good and smooth" surface it wastes a lot of pedal work. On an undulating surface it wastes a lot of forward velocity and pedal work

I'm asking for the 3rd and last time - PROVE IT

I'm no cyclist, but I can definitely feel a suspended pedal bike suck up leg power requiring more effort than a bike with no suspension, same tires and road.

Are you talking about rear suspension? Is that the bike with the extended swingarm?

 

[amberwolf]

Simple test that should determine the answer to the suspension energy question:

Take an electric bike with power metering (CA, etc) on it. Prepare a dyno for it, indoors, to control all the "ride" conditions.

Put regular tires on it, and a "rider" but no pedalling. (eliminates suspension bob due to pedalling as a factor)

Run it on the dyno, gather the numbers on power usage.

Alter the tires so they are out-of-round significantly, as if you were riding on a bumpy or "wavy" road surface, that would cause suspension to begin working. Or if the dyno can be altered, set it up to emulate that road surface type instead. Doesn't matter, as long as the suspension begins doing it's thing.

Run it on the dyno, gather the numbers on power usage.

If you have exactly the same throttle settings, then if the suspension does not cause momentum loss, the results should be identical. If they are different, then the reasons for it would need to be determined, but should be simply the suspension action.


I might've missed some conditions necessary for the test, but it should still be possible to do this type of test and answer the question easily enough.

 

[full-throttle]

@AW: Are you comparing rough vs smooth or suspension vs rigid? Sounds more like the former to me.

 

[amberwolf]

I dunno. Whatever way would be best to determine the effect. If you can lockout the suspension then the latter would be easy to test, right?

 

[e-beach]

Simple test that should determine the answer to the suspension energy question:.....

A fastening of the bike to the test apparatus could be tricky as a bike on a dynamometer tends to want to pivot at the head set. The back wheel tends to kick laterally. The back of the bike would have to be secured in a way that would not influence the test.

I think a treadmill test with one smooth belt and one bumpy belt would be a better indicator. A tweaked rim has an over-abundance of bumps. In other words, one bump per revolution is a lot of bumps. It might be indicative of ruff terrain, but not city riding where the bumps come with less frequency then every 2, 3 or 4 feet continually.

Also, suspension bob due to peddling is a fact of life on rear suspension bikes. That would need to be tested as well because of the need to peddle up hills and such.

It might be easier to test three bikes, one rigid, one hard tail, and one fully suspended, all with as similar frame design as possible, all of the same weight (weight added of subtracted as needed) one rider, one motor and one battery pack that would be switched to each test bike as needed and then run them over a series of road conditions. First up wind and then down wind, throttle set to go wot easily, at a reasonable speed for the bike so "under-throttling" would be eliminated in the test.

Then the real kicker would be to have a front wheel motor to test the difference in efficiency of being pushed vs being pulled while suspended or not.

Sounds like a very doable test.

 

[melodious]

Maybe I can be the voice of common sense. Who knows...

Chalo made a very good point a few comments back. "Racing road bikes have regulated minimum weights that would allow them to have suspension and still weigh the minimum. None-- as in zero-- of them have any mechanical suspension at all. It's not for lack of budget, or because guys racing 120 miles a day at full tilt couldn't use some extra comfort. Manufacturer sponsors would love it, because it would allow them to sell a bunch of really expensive toys to eager tools. Suspension road racing bikes don't exist because they would lose. And that's at e-bike speeds or more. "

I think it's a waste of time to dyno bikes just to prove (or disprove in this case) a point. The only thing that is really grabbing my curiosity is how much of a difference in energy is one vs. the other. These are bikes with probably 20ah of batteries in them. Is one bike going to go 1/2 mile further? If so, then pedal the rest of the distance to equal the "more efficient" bike. It's not that hard to do.

I'll put it another way. Replace the bikes with cars. One car has suspension the other hasn't any suspension. Same drivetrain, same aerodynamics, etc. The rigid car would win. It would be a pile of loose nuts and bolts on the ground, but a winner none the less. :wink:

 

[Ozjet]

I'm doing my first build as a dualy, I was put of them by the shop re bob and bought a ridged, but then figured I got a motor so a lot of that should be negated, so much more comfortable, haven't riden it yet with the motor , and it is all good as 100 percent gruntwheel, that's not yet using the adjustments on the fox shock to make it stiffer

 

[full-throttle]

Chalo made a very good point a few comments back. "Racing road bikes have regulated minimum weights that would allow them to have suspension and still weigh the minimum. None-- as in zero-- of them have any mechanical suspension at all. It's not for lack of budget, or because guys racing 120 miles a day at full tilt couldn't use some extra comfort. Manufacturer sponsors would love it, because it would allow them to sell a bunch of really expensive toys to eager tools. Suspension road racing bikes don't exist because they would lose. And that's at e-bike speeds or more. "

Another example of correlation doesn't imply causation. I could say the average speed of athletes increased since the introduction of suspension, so suspension must be good then.
His claim is not even true - Paris-Roubaix has been won with suspension equipped bikes several times.

When surfaces are good and smooth, mechanical suspension throws away a lot of energy that could be used to propel the bike, or to keep it rolling

Well since Chalo can't support his own claim I can disprove it instead:

Assuming by "a lot" he means 10W converted to heat, the temperature increase in a typical suspension system, assuming 500g equivalent weight of oil with specific heat of 1.8kJ/(kg*K) will be equal to 40*C after one hour.
Does a suspension fork feel too hot to touch after a XC race? No! Yet a typical race goes for 2hrs, the surface is far from being "good and smooth" and there's a lot more pedalling involved than on an e-bike. Does it even feel warm?

BTW a 10W loss would decrease the speed from 40kph to 39.7kph on an unsuspended MTB and from 40kph to 39.5kph on a road bike. Switching from unsuspended MTB to a road bike would save 200W though!

 

[Chalo]

Knobby tires don't get noticeably hot either, but they noticeably slow you down. I think forced air cooling is a factor in both cases.

 

[full-throttle]

Knobby tires don't get noticeably hot either

That's because a large proportion of energy loss in a tyre is sound

 

[Chalo]

Knobby tires don't get noticeably hot either

That's because a large proportion of energy loss in a tyre is sound

!!??

 

[e-beach]

Knobby tires don't get noticeably hot either

That's because a large proportion of energy loss in a tyre is sound

!!??

Yea, I was wondering about that also......

full-throttle, can you extrapolate on the "energy loss in a tyre is sound" concept? I am definitely curious.

I'm thinking that vibration of tire rubber against certain surfaces causes audible sounds, but in a vacuum where no sound would be audible, energy loss through friction would exist....I don't get what you mean. Are you saying that it would take longer for a bike to slow down in a vacuum because no sound would be created? Help me out her because I don't understand.

 

[full-throttle]

Rolling friction generates sound (vibrational) energy, as mechanical energy is converted to this form of energy due to the friction. One of the most common examples of rolling friction is the movement of motor vehicle tires on a roadway, a process which generates sound as a by-product. The sound generated by automobile and truck tires as they roll (especially noticeable at highway speeds) is mostly due to the percussion of the tire treads, and compression (and subsequent decompression) of air temporarily captured within the treads.

for the lazy

 

[t3sla]

Heat, sound and light all use energy.
Squeaky breaks, energy loss.
Sparking commutator, energy loss.


Basic laws of physics, energy isn't made it's transferred

 

[winkinatcha]

AHAHAHAHAHA!

Joe

 

[Chalo]

Rolling friction generates sound (vibrational) energy, as mechanical energy is converted to this form of energy due to the friction. One of the most common examples of rolling friction is the movement of motor vehicle tires on a roadway, a process which generates sound as a by-product. [...]

for the lazy

I just don't think you understand how much noise a watt of energy can make. Efficient speakers can make over 103 dB per electrical watt at a distance of one meter. That's after efficiency losses in the speaker mechanism.

Yet you're saying knobbies don't noticeably heat up (many watts required) because they're making noise instead?

No wonder you seem to have difficulty ranking other power sinks by magnitude.

 

[Ken Taylor]

Interesting about the road race bikes. I thought they all had the lightest construction bikes possible...part of the science of the sport.

Minimum bicycle weight in road racing is for safety reasons. Professional cyclists will do whatever it takes and will reduce weight to the point that breakage is likely if it's allowed. Because the minimum is a kilo or more above what can be done safely it allows live race tracking without performance penalty. Like drugs in the past though, its poorly enforced so riders frequently don't like the extra 130 grams or so of extra weight that tracking requires. Unfortunately live (but not post race) tracking is banned at the moment but I'm sure that will change.