I've ridden both clipless and platform pretty extensively. on a lot of my group rides, I've shown up in toe clips and hiking shoes, and people thought I was really strong to still be able to keep up. but to be honest, I don't find any loss in performance riding platform unless I'm accelerating or in an all out sprint, where the upstroke actually plays a role in my pedaling output. And while this is important in competitive situations, I don't believe this is important for casual riding or touring. even when climbing, most of that effort is spinning, until the rider stands up and starts pulling the pedals on the upstroke. So I felt compelled to find some evidence supporting clipless in pedaling efficiency over platform pedals.
Here's a video of them testing clipless and platform
Granted, this experiment with only 1 data point is not too convincing. So I pulled this off of another forum that someone posted. It indicates that while the upstroke does play a role in clipless setups, it actually decreases your mechanical efficiency, which support the idea that the upstroke is only relevant when you're trying to beat someone up a climb or to a finishline/corner - it's not sustainable in a long ride.
Abstract
The aim of this study was to determine the influence of different shoe-pedal interfaces and of an active pulling-up action during the upstroke phase on the pedalling technique. Eight elite cyclists (C) and seven non-cyclists (NC) performed three different bouts at 90 rev · min−1 and 60 % of their maximal aerobic power. They pedalled with single pedals (PED), with clipless pedals (CLIP) and with a pedal force feedback (CLIPFBACK) where subjects were asked to pull up on the pedal during the upstroke. There was no significant difference for pedalling effectiveness, net mechanical efficiency (NE) and muscular activity between PED and CLIP. When compared to CLIP, CLIPFBACK resulted in a significant increase in pedalling effectiveness during upstroke (86 % for C and 57 % NC, respectively), as well as higher biceps femoris and tibialis anterior muscle activity (p < 0.001). However, NE was significantly reduced (p < 0.008) with 9 % and 3.3 % reduction for C and NC, respectively. Consequently, shoe-pedal interface (PED vs. CLIP) did not significantly influence cycling technique during submaximal exercise. However, an active pulling-up action on the pedal during upstroke increased the pedalling effectiveness, while reducing net mechanical efficiency.
What do you think? I feel like the whole argument that clipless being more efficient than platform pedals, while true in certain situations, is mere exaggerated hyperbole in most other situations. Foot retention is also important for a variety of reasons, but platform pedals can do that very well with toe clips (imo) for road riding anyway.