why?

I rely on frame members for comfort on my full suspension mountain bike, and it's faster than a fully rigid mountain bike.

what's the difference, except in degree? (bearing in mind that some of us live in areas with really bad roads, having a "reserve" of shock absorption for pavement cracks, frost heaves, expansion joints,

besides, what I'm thinking of would have no effect on aero, you would still run tire pressures the same as an unsuspended bike. there would be literally zero penalty other than maybe 20-50 extra grams of mass in the seatpost and stem....

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That's why I said "road bike" ;-) it's a different use case than a MTB, or even a CX bike, in that the surface roughness typically travelled is orders of magnitude smaller.

Allowing the tires to "act" as the suspension means that the majority of the energy compressing the tire in the leading half of the contact patch is able to be returned to the road surface in the trailing half (assuming the tires used don't have high hysteresis). Once that energy gets past the tire and into the wheels and frame, then the only option is for it to be dissipated as heat somewhere in the bike or in the rider contact points.

Since, by definition rolling resistance is the direct result of the difference in energy put into the leading half of the contact patch and the energy returned in the trailing half (and the resulting torque about the axle from that difference) it makes sense to make sure the energy doesn't make it to a place it can't be as efficiently returned as with the tire...IF the use case allows, of course :-)
http://www.slowtwitch.com/...ling_events_226.html

Oh...and for those frost heaves, etc...that's what bunny-hopping is for ;-)

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http://bikeblather.blogspot.com/

right... but you don't need to change the tires to implement a change to the seatpost / stem. most vibrations won't make it past the tires, if they do, then they are being dissipated as heat anyway. so why not have them dissipated as heat in my seatpost or stem, rather than in my taint... and if I don't have to stop outputting power to the cranks and have my rear wheel leave the ground to bunnyhop an obstacle, then I'll be faster....

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Like I said, if you figure out how to make the tires "work" (be it by tire/tube choice and/or pressure) you'll be overall more efficient than if relying on those frame elements to do that same job.

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http://bikeblather.blogspot.com/

while there might be some flex noticeable in the seat post, I don't think you could feel the difference with the aero seatpost once riding on the road. At least I could not. I challenge anyone to try. perhaps I m just not itune with myself!

the next step would be a 2-3-4h blind test to see if those difference are noticeable. But I don't see why they would be...

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you still haven't pointed out the downside of having a suspension element in the seatpost and stem.

the tires will do the same job, you will still have the same choices with respect to tire size and pressure. since the tires are the same, no additional energy will be transferred past the tires into the frame, just that the frame will absorb that energy that makes it past the tires rather than my soft tissue.

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Nothing wrong with that...except for carrying around extra mass and/or the added compliance taking away from aerodynamics (in order to engineer it in place) or handling/power transfer...for something that happens rarely in a ride or event (energy getting past a properly selected tire setup, that is).

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no aero effect. my thought is that tube shapes would be the same (think carbon leaf springs embedded in the seatpost with an elastomeric element for damping...).

You obviously dont ride on Canadian roads if you think that pavement cracks are rare (or small....)

20 - 50 grams of mass is irrelevant. You know that already....

I'm not seeing the downside here. obviously this wouldn't necessarily be an easy thing to engineer, but for those of us who live in areas where the roads are completely shite, it would be a nice option to have available. because its in the seatpost / stem, then if you don't want it because you "think" it will make you slower, don't get it...

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Swimming Workout of the Day:

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I lived my first 22 years in Wisconsin, so I get what you're saying.

All I'm saying is that if that was what I rode on all the time, I'd probably have the largest tires possible on my regular bike (or get a bike that allows even larger tires) and keep things simple :-)

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