I think you should upgrade your front wheel, too. But first, upgrade your breaks so that you can handle the extra burst of speed.

+1
Spongy.

Not sure I agree. I haven't seen studies about spoke tension effecting efficiency. But I do know the difference between feed back and efficiency. That so many people don't is why there's the misbelief that fatter tires are slower then skinny ones. Slow reaction is not less speed. Andy.

I believe the phrase you were actually looking for was "drope the hamer".

I believe the phrase you were looking for when you helped him find the phrase he was looking for was "drop the hammer."

You couldn't possibly be more mistaken.

Incorrect. This is BF, it's "drope the hamer".

Well, I haven't done any studies, but I've killed more rear wheels than I care to count. One thing I started noticing was that it felt like it was taking more and more energy to climb the hills I have to climb every day. Then, inevitably the wheel would finally really show me that it was toast by starting to break spokes. As soon as I put in a new, properly trued wheel, it was amazing the difference I felt. It was like the difference between heading out on my commute on a day where I got enough sleep and had a decent breakfast versus the commute home after working an overnight shift and not having eaten for hours.

Makes sense to me that a wheel that is mushy from all the spoke tension being gone would rob you of a lot of the energy that should be propelling you forward.

My zwei pfennig anyway.

Medic Zero- In no way am I saying that a loosely spoked wheel is right or what we want. The condition will have other consequences (broken spokes, rubbing brakes, etc) that are not conducive to finishing a ride quickly.

But if put in isolation of these other issues does a "soft" wheel retain energy? I'm just not sure how much looseness creates how much energy gain (as in how much energy is transfered from the forward rolling of the wheel to friction of the spokes rubbing against each other or against the hub/rim holes).

Once again, I maintain that most people confuse the issues at play when talking about what is perceived VS what is actually going on. Andy.

I have no analysis to back it up, but my gut feel agrees with Andrew R Stewart's post #34 . I.e., by the time the spokes are loose enough to result in significant energy loss, you're facing other, more immediate problems, notably high risk of tacoing a wheel.
The situation you want and is the design intent of a spoke wheel is that the static tension is high enough that the variable tension due to load reversal on rotation is a reasonably small fraction of the static tension, (and preferably less than 20% of the UTS so that we are within steel's fatigue limit, i.e., assuming steel spokes).
But unless variable tension is approaching 100% of static tension, I see no great absorption of energy through this mechanism.

It's easy to forget that the only way the whole damn contraption (you + bike + Fredly gear + etc.) is connected to the road via the tires+rims is through the spokes -- those flimsy little things. The hubs don't hover on their own, they are held up by the spokes and all the forward/backward force of accelerating and braking is translated into lateral and rotational forces in the wheel that are transmitted through them, too.

Once that is in perspective, it should become a bit easier to ponder that lousy spoke tension just makes for a sloppy ride with wasted energy going everywhere, +/- causing problems in the spokes/wheel. The numbers that were kicked around here seem to be for a pretty sloppy wheel, YMMV, but they're not wacky.

Ever try running in soft beach sand, vs. hard sand (say at water's edge) vs. pavement? You won't be setting a personal best in the sand. Loose spokes on a bike are like soft sand for a runner. Until they break, then they're worse.