[Mark McM]

Originally Posted by marciero

Sure, he could have done a lot of things to compare with flex in other places. But he wasn’t out to do that. He demonstrated pretty convincingly what he set out to show: fork blades flex, and not an insignificant amount if they are of a certain design. Note that the low rider hoop rises about 3mm as it gets closer. That is pure vertical deflection, and not "amplified" through a large radius. And to my eyes, the video does not show there is "far more flex in the rest of the system".

The tire is part of the system, and clearly flexes more than 3mm. Plus, this test only simulates landing on a flat surfaces - when hitting small radius bumps (such as cobbles or the edges of potholes) the tire flex will be even greater, and the relative contribution of fork flex will be less.

Originally Posted by marciero

Most of us can feel very small amounts of frame flex in the ride. One bike has "all day comfort" while another one beats us up. Those sensations are about very small amounts of frame flex. And here we have a not insignificant amount of flex right where it has the most influence on the ride.

Actually, blind testing has shown that most riders can not feel small amounts of frame flex. Here's some comments from Josh Poertner regarding blind test of frames and wheels while he was an engineer at Zipp:

I've participated in numerous blind product studies over the years where we controlled bikes or the wheels (I've done this twice with a bike manufacturer during development work around a pro team, and many times with wheels) with fabric shield tensioned between seat post and stem, flat black rattle can paint on everything, etc. In each of these studies, the entire subject group including pro riders, engineers, and other industry people with LOTS of experience, struggled to find any real differences between any of the bikes, until after the study was de-blinded and everybody (including me) instantly began to try and rationalize it all… This is just human nature, we all do it, and from experience, it is nearly impossible NOT to do it.

One of the major discoveries was that after controlling for seat post (round post shimmed into aero frame so as to not give it away) not a single rider found the aero road bike to be less comfortable, less compliant, etc, than the identically setup 'endurance' or 'roubaix' bike (clearly this leaves room for the aero seat post to be why people feel aero bikes are less compliant..seatposts generally have more effect on bike compliance in the lab than frames do, but that's another story). We ran blind wheel tests a couple of times a year at Zipp to benchmark competitive wheels and our own prototypes, and we also found that blinded riders were generally unable to tell the difference between stiffness and inertia, had no reliable feedback on weight, lateral stiffness, or comfort in general, and in the end were generally only able to pick out the aero wheels because they were riding laps around a closed park environment using power, so the more observant ones would notice speed differences. In the end, we sort of determined that when riders didn't know what they 'should' feel, they really struggled to find differences in stiffness, compliance and weight between frames or wheels. The strongest correlation we ever saw was to tire pressure, but not in the way you would expect. Almost everybody assumed the setups with lower tire pressure to be the endurance bike and would then score it exactly as you would expect a magazine review of a comfort bike to look…so we determined that we all naturally would latch onto something we were confident in, in this case comfort, and then would proceed to perceive everything you expected from that bike: less aero, less stiff, better damping, etc. Imagine the shock for the group when it turned out that the it might have been a super stiff race bike, or an aero road bike! Let the rationalizing begin!

Others have also done blind testing of frame compliance, and had similar results.