I thought frame flex was not a problem, in and of itself. It is the hysteresis involved in the flexing that saps your energy.

If you can reduce the flexing, you can change/reduce the hysteresis.

If you change the frame's materials, you can change/reduce the hysteresis.

If you change the frame's geometry, you can change/reduce the hysteresis.

My Raleigh Grand Prix (1020 tubing?) used to suck the life out of my legs, especially when climbing. It just would not respond to being pushed hard. It seemed the harder you pushed, the more energy was wasted. My Bob Jackson, with its 531 tubing , is a relative rocket ship. It does not bend as much and seems to rebound when it does bend. It climbs as well as you could hope (pilot-limited). The two bikes have different materials and different geometries.

C&V Grand Prix's are seemingly in favor right now for some reason. Personally, I will never buy another one.

Interesting! The wiki definition includes this line..."Hysteresis can be a dynamic lag between an input and an output that disappears if the input is varied more slowly; this is known as rate-dependent hysteresis.

My fave steel ride was a flexy 022 frame and there was this sweet spot when you felt the frame flex giving back everything you put into it, very elastic. I think flexy frames are often easier on your body and give some energy gains in return.

But a stiff C-dale is still the bike I'd want for any final sprint

I was thinking of hysteresis in terms of energy loss per cycle. The time delay (dynamic lag) is an "instantaneous" delay within the cycle.

Push a spring hard and fast. It compresses instantaneously but it also rebounds (car suspension) but it never gives back everything you put into it. The energy lost contributes to making the spring heat up and fatigue.

I get that there's loss, there has to be. But we all appreciate steel's ability to tolerate some flex for decades before weakening and it's the fact that the tempo can change the efficiency of the steel to minimize loss and return variable amounts of the original input that I find interesting.

My Flyte SRS-3 is a pretty burly aluminum frame that is on the heavy side. I always feel a little lethargic on it at mild speeds of 13-16 mph. Strangely, it seems to become a different bike if I am more fit and ride in the 17.5-19.0 average speed range. I always thought of it as akin to having really stiff suspension on a sport model car compared to the standard model’s softer suspension.

My other aluminum bike, a Cannondale R1000 CAAD3 is also stiff with its straight, burly seat stays. I use Selle Italia Turbomatic saddles on all my bikes & they do a pretty good job of taking the sting out (for the butt region of the 3 contact points) of oversized aluminum’s rough ride.

I loved my Super Criterium 800, but after about 30 miles, going fast was not that much fun.

I hated my R800. Hated it. Hated it.

I loved my Six13.

But I like a lot of bikes, and if the fit is good, and I feel good, they are fast. If not, not.

From 15.7 lbs to 22.3, that's pretty consistently so. I actually prefer certain cassette/chain ring combinations to specific bikes.

And lately, riding with girls.

fify

That certainly fits with my observation - push hard but don't go much faster.

My fastest bike has, in effect, variable chainstay length. It is always fast. (It's a fix gear with a long dropout that I have used all of, from the tire almost touching the 75 degree seat tube angle to the wheel pushed all the way back (~2" travel).

I think a very large part of how fast a bike is is in our head and how the bike "feels". That "fastest" bike of mine is a fix gear designed basically as a 1980s race bike except road fixed. Quick race steering, high-ish BB, bar location that is pure race for this body. As soon as I start riding the bike I am aware I am on a race bike. I almost cannot ride it as an "ordinary" bike.

Now, my fastest ride times are not on that bike. Fix gear. I haven't strava'd any climbs but I suspect I done a few on it I will never match on another bike. (I look at that bike as my "mistress" - no, not a concubine, but the feminine of master. Very much a she and very much in charge.)

Ben