Full suspension VS no suspension

[TylerDurden]

If you think of suspension units like bike tyre pumps (which they are very similar to in many ways) then it's clear that when they move they convert some of the energy put into the piston rod into heat.

A rigid frame bike also does this to some extent, as the frame deflects under load it also warms up a bit. The major difference is one of scale, a rigid frame does not deflect anywhere near as much as a suspension unit, so absorbs less of the riders energy.

Ok, here's another take:

The kinetic energy of the bike & rider are generated soley by the rider.

That kinetic energy is re-directed by a bump.

In the ridgid frame bike, the bike and rider are both lifted vertically.

In the FS bike only the suspension elements are lifted.

The FS bike allows less energy to be lost by conversion into potential energy and retains more energy in the forward momentum of the bike & rider.

So why does the shock warm up?
Pressure, of course.

And so, what of the ridgid bike?
Same thing, but you don't have a convenient place to concentrate the pressure... it is spread throughout the tires, where you can't feel it. After all... you pump up a tire and the pump gets warm from the pressure; the same pressure is in the tire too. Does it feel warm? No... the energy is so spread out, us mere mortals cannot distinguish the temp rise, but it is there.

Try this: take any rubber band (fatter is better) and hold it against your cheek as you stretch it... it will feel hot. Keep the rubber band stretched until it cools off. Then relax the rubberband against your cheek: it will feel cool.

So, in the case of hitting bumps, the tires of a ridgid frame are heating more than the shocks of a FS, because all the mass of the bike and rider are moved, compared to just the suspension elements of the FS; you just can't feel it cuz the tires are so big.

 

[Jeremy Harris]

For really big bumps, then I doubt that there's any significant difference between a the energy loss from a suspended bike or a rigid frame.

However, when looking at the very small deflections from uneven road surfaces etc, (which is what I was referring to, as it represents the vast majority of riding time for most) then the rigid frame is better at putting the energy from the bump back into useful work. This is what I've been trying to describe.

Imagine a small bump, where the tyre remains in contact with the ground. As the wheel hits the bump, first the tyre deflects, then the bike (or suspension) deflects upwards.

As the wheel rolls over the top of the bump, some of the energy used to lift the bike will act to slightly push the bike forward on the down slope side.

With a hard tyre and a rigid frame, this will happen quickly, so that more of the energy is converted into useful work before the wheel rolls off the bump.

With a suspension unit, this will be delayed, so some of the energy won't be returned as downward push until after the bump has been passed (the suspension works by absorbing fast bumps and spreading them out so they seem like very long, gentle ones).

This is one reason why suspension (or a frame) will be less efficient when road riding.

Off road then efficiency takes a back seat to the need to keep the tyres on the ground, as has been said already, a wheel that's not on the ground isn't much use.

Jeremy

 

[safe]

Suspension is MORE efficient

First... if you've followed the suspension saga over the last 20 or so years like I have you know that in the beginning they didn't understand how to eliminate the "pogo" effect of the rear end when pedaling. Now thay have... if you can get your rear swingarm to follow a path so that when you apply pressure on the chain through the crank that the result is NEUTRAL then there is no rear suspension squat.

Getting past that point (and many people seriously aren't aware of the long quest and final conclusion of that dialog) the remaining issue is the response to bumps.

Do not forget the tires!

Every time the tire hits a bump and is forced to deform itself it produces a very large amount of losses. When the bumps get larger the tire needs to literally lift the entire frame up off the ground in order to clear it. That lifting subtracts from forward motion and slows you down. (it's effectively redirecting energy into little rocket liftoffs that then fall back down to earth afterwards) Suspension simply allows the tire to AVOID lifting the frame off the ground and allows the bike to travel in a straight line.

On most road courses the bumps are so minimal that the extra weight is not worth carrying in order to save little bits of energy on the bumps. However on cross country dirt bike riding they went through years of debate over suspension vs non-suspension and the results seem to depend on the track that is being ridden. On the downhill efficiency is not an issue and basic rider control takes over as a more significant issue.

So the answer is that suspension (done well) will always be more efficient than non-suspension, but other factors often play into the mix in real life...


http://www.totalbike.com/news/article/506/

 

[safe]

The kinetic energy of the bike & rider are generated soley by the rider.

That kinetic energy is re-directed by a bump.

In the rigid frame bike, the bike and rider are both lifted vertically.

In the FS bike only the suspension elements are lifted.

The FS bike allows less energy to be lost by conversion into potential energy and retains more energy in the forward momentum of the bike & rider.

Well said...