pacificcyclist

While I don't ride in Toronto, in Vancouver BC along River Dr in Richmond my front MEC bag which is almost exactly like the Brompton T-Bag that is in front of my Speed Uno presents negligible wind drag in heavy head wind conditions (just today is nasty in the early morning commute) compared to say a pair of touring size bags hanging on the sides. I've done some scientific tests and I have concluded that unless you are cycling faster than 20mph, then other things on the bike and your riding posture are slowing you down. Although I realized my MEC cycling rain cape presents the most aerodrag when worn.

The Brompton is not exactly a speed machine per se, not as stiff as a Tern Verge or my Mu SL. Even the Speed Uno is slighter stiffer than the M6L and there is a reason for this. I think what you are experiencing is frame flexing as you are putting more power to the pedals to combat the head wind. You can't help it as the upright riding is conducive to a poor drag coefficient -- more front area exposed as opposed to a time trialist on a Cervelo S5. As you are putting more effort on the pedals, the frame needs to be stiff enough around the BB and rear triangle area to allow the transfer of pedal power directed towards forward propulsion. Unfortunately, the Brompton has a suspension thingy on the rear and while it helps cushion the blows from rough roads, unfortunately the suspension robs some of your pedaling power in a form of "frame flex" and suspension movement from pedal induced motion (bobbing) -- it's essentially a URT design (Unified Rear Triangle) like the infamous Trek Y bike of the past. In fact, you can improve the stiffness of your Brompton by replacing the soft suspension block with a much firmer version to try and lock it out. Peter at NYCEwheels commented exactly that as some one commented why riders on the demo video is putting a lot more effort moving the bike forward even in an isolated bike path under the bridge than need be! Peter commented that it was the suspension block that is robbing some of the pedal power flexing the frame. I concur as I rode the B and noticed the flex under stress. This is also the very same reason why some touring cyclists mistakenly assumed that it was wind drag at 10mph that had caused them to cycle with more effort with panniers when in fact it was frame flex that make the panniers wiggle (most cyclists wiggle side to side to a varying degree) that some of that pedal power went to move the bags rather than mainly moving the bike forward. Which is also the reason why a correctly designed loaded touring frame is equally stiff and heavy to combat frame flex from the movement of the heavy panniers so it allow the rider pedal power to get to where it needs the most -- move the rear wheel!