They've done studies in the lab on a bike on a trainer on pro racers and less formal experiements with amateur racers.
Assertion: Clipless is in inherently faster.
Result: False. Clipless vs flat shoes measure exactly the same speed/distance in the lab.
It's Not About Pulling Up: Why Flat Pedals Work | Nourish Balance Thrive
Effect of Pedaling Technique on Mechanical Effectiveness and Efficiency in Cyclists, Korf et al. DOI: 10.1249/mss.0b013e318043a235
Effects of Pedal Type and Pull-Up Action during Cycling, Mornieux et al. DOI 10.1055/s-2008-1038374
Both studies offer compelling evidence that support the idea that clipless pedals offer no mechanical advantage over flat pedals.
Assertion: Clipless lets you pull up with your hamstrings so it's faster
Result: Ekg's showed that pro racers unweight the pedal that's going up but do
not pull up with their hamstrings.
One can change their pedalling technique to use the hamstrings but the results say that people winning races are not doing it so it's most likely not the strongest/most efficient way to pedal.
https://www.quora.com/Are-clipless-p...more-efficient
Thomas Korff reported in Effect of Pedaling Technique on Effectiveness and Efficiency in Cyclists that gross metabolic efficiency was lower when cyclists were instructed to pull-up (19.0+/-0.7% versus 20.2+/-0.6%).
Assertion: Clipless is more efficient.
Result: I haven't seen anything that shows a major difference. In close differences, one study will say clipless is a hair more efficient, another one will actually suggest flats are a hair more efficient. And these studies are on people who have been training and racing with clipless so if anything you'd think they'd start off with a clipless advantage. The conclusion to me is that any difference is to small to consistently measure.
Assertion: Clipless gives you an advantage in being able to pull up and do short sprints faster (though at the cost of more energy).
Result: There aren't really any results on this as it's to hard to measure and do a scientific study on. It's possible. I've seen more casual videos testing this out and being faster in a short sprint with clipless. Keep in mind that it's a cost tradeoff - you expend more energy but go faster for the sprint.
Assertion: Clipless attached to the pedals better than flats.
My Experience: My feet wouldn't stay entirely secure on the plastic pedals with regular shoes. I saw I could buy pedals with rougher edges that were better for grip but they looked like they might have issues with foot comfort. What's really improved grip is Five Ten flat shoes...they use a special grippy rubber that together with pedals with pins makes them grip the pedal so much I have to lift my foot off the pedal to reposition it (or I could remove some of the pedals pins). They grip the pedal solidly down, forward, and back. Vs Clipless, obviously clipless continues to grip if you pull your foot up while flats do not. That's also the learning curve you have with clipless that you don't have with flats though - learning to clip out by twisting your foot to the side, rather than the natural motion of pulling your foot up off the pedal. Again I could see how clipless could be an advantage for people racing who are in a wild all out sprint in a pack of riders and keeping your foot solidly connected to the pedal. Not really a situation I run into in average riding though.
Comfort: Some people are equally comfortable with either one. I think a lot of people are going to be more comfortable with flats. I personally am - clipless gave me knee pain and hotspots on my feet when riding. On the other hand, some people on the forum have said their particular leg pain was solved by a professional fitter putting them on clipless and locking their feet (with clipless) into the ideal position on the pedal.
I use Five Ten Freeriders and Dmr Vault pedals and it's by far the most comfortable I've ever been on the bike.
https://www.adidasoutdoor.com/five-t...07_color=Black
https://www.dmrbikes.com/Catalogue/P...lt-2/Vault-NEW
Clipless is a good system. If people ask me what they should wear I say either flats or clipless. My one beef with clipless is mainly the overhype and some people putting people in dangerous situations trying to pressure them to use it. To use clipless safely it does require getting used to the "twist to side" motion to unclip. A few people never acclimate to it which would make clipess dangerous for those people. I'm not a fan of the "I bought some clipless last week and through them on the bike now I'm going on a long fast ride today hope I can unclip" philosophy. The other group of people is people who falling over at any speed is most likely going to seriously injure or kill them. I mean if you're already used to using clipless it's fine but like my dad is part of a seniors bike club and there's one guy who's always trying to talk the other senior into switching to clipless. If you're 75 and likely risk permanent injury if you fall over, there's absolutely no reason to try clipless at all. It's all completely unnecessary risk.
If I was racing I'd probably go back to trying even more stuff to get clipless to work for me, but I'm not, so I find the convenience of flats along with the "basically no difference in speed" far more appealling. I love that I end a ride with my feets and knees feeling just fine with flats. Many people don't have problems like that with clipless but I did. I enjoy not having to switch between 2 pairs of shoes every time I ride. I do wear bike-specific five tens but I often just keep wearing them until the end of the day after riding because they're the same comfort as my regular shoes. I enjoy not having the small mental overhead of remembering that I'm wearing clipless on the bike, and not having to worry I'll put a cleated foot down and fall over because I'm on some more slippery surface (like those painted crosswalk lines). I personally definitely prefer flats.