The authors were from Italy and though they make no specific mention of the brand and model, they supply a side profile image. The shoes were both Sidis, with buckled version an Ergo 2, while the lace-up appears to have the exact same sole, but slightly different upper (obviously, being laced).
Since at the time the Ergo 2 was in widespread use, I would think their choice was a good one. Also, I would say the buckle was no more obtrusive than any other.
As for the difference in watts, I was looking only at the increased requirement in translational power. The authors broke down the pedal action into rotational and translational components. Shoe weight plays much more of a roll in rotational and a lace-up tends to be lighter. Therefore, the total difference is a little more than 5W as the "buckled" and "buckled + overshoe" are penalised again for weight increase over the lace-up.
In another study from different authors, focused on bike position, they noted that one of the biggest factors for drag reduction in clothing (anywhere) is that it stays flat. Obviously you can try and make something that gussets a particularly draggy part of the body, but barring those sorts of tricks, not wrinkling was key. Pretty sure all the aero engineers on here would have already said as much.
So, why did I say that? Well, think of a shoe cover, whether it's simply lycra or some fancy vinyl coated bootie. It might not be too hard to design one that covers the shoe smoothly, but much harder to get the transition from shoe to lower leg smooth and wrinkle free, particularly when you consider the entire pedal stroke. Meanwhile, your skin does a great job of not wrinkling up -- given rider age (hah, I kill me) -- so just getting a clean fitting shoe that ends flush with the top of the foot would probably work best for the widest range of people.
Since at the time the Ergo 2 was in widespread use, I would think their choice was a good one. Also, I would say the buckle was no more obtrusive than any other.
As for the difference in watts, I was looking only at the increased requirement in translational power. The authors broke down the pedal action into rotational and translational components. Shoe weight plays much more of a roll in rotational and a lace-up tends to be lighter. Therefore, the total difference is a little more than 5W as the "buckled" and "buckled + overshoe" are penalised again for weight increase over the lace-up.
In another study from different authors, focused on bike position, they noted that one of the biggest factors for drag reduction in clothing (anywhere) is that it stays flat. Obviously you can try and make something that gussets a particularly draggy part of the body, but barring those sorts of tricks, not wrinkling was key. Pretty sure all the aero engineers on here would have already said as much.
So, why did I say that? Well, think of a shoe cover, whether it's simply lycra or some fancy vinyl coated bootie. It might not be too hard to design one that covers the shoe smoothly, but much harder to get the transition from shoe to lower leg smooth and wrinkle free, particularly when you consider the entire pedal stroke. Meanwhile, your skin does a great job of not wrinkling up -- given rider age (hah, I kill me) -- so just getting a clean fitting shoe that ends flush with the top of the foot would probably work best for the widest range of people.