Stiffness/Power Transfer
Despite its ultra-thin profile, adding only 4.3mm of stack height, the Carbon Air-Lite outsole provides surprising forefoot rigidity for outstanding power transfer. The shoe is also the lightest in our test – comparable to high-end racing shoes. Testers never felt any give even under heaviest efforts despite three airflow holes (which also reduce weight) including a very large one under the heel. However there is some noticeable torsional flex (twist), but with proper alignment and position on the bike riders shouldn’t notice this. Only when testers really wrenched their bike side to side did they feel the minor give.

Power transfer can also be gained or lost in the shoe’s upper, depending on how much “give” exists when the shoe is tightened down. We were able to dial in a very tight fit on the LS-100 with no discomfort, and testers feet had negligible movement in the upper – especially in the critical heel cup which kept narrow heels in proper position, even on the sprints. The well-padded yet well-ventilated tongue allowed testers to crank the Boa with no pinching. However riders with narrower feet may feel some forefoot movement.  

Fit/Comfort
With a supple yet sturdy synthetic upper, and smooth soft inner lining, plus a plush heel cup, the LS-100 feels more like an endurance shoe rather than a racer, despite its high performance. The upper wraps smoothly with well-designed contouring, and the gentle toe arc in the outsole is less severe than more serious racing shoes, which adds to the comfort for endurance efforts. There are a few stich seams, but these were never an issue during our testing. While there’s little, if any, arch support, which may lead to discomfort on longer rides, testers never noticed any issues, using their own insoles. Finally the 7mm of adjustment allows for exact placement of the cleats for the best power transfer and comfort.

Closure System   
While we’re big fans of dial closures in general, lower-end recent models (and all early models) only allow for one-way tightening, and do not provide a micro adjustment when loosening. So while the right shoe tightens in the usual “righty tighty” manner, the left is reversed. And to loosen these dials, you have to pull up to release the tension. But this is an all-or-nothing system – when you pull up the line releases completely, so you have to re-tighten all the way again. Definitely not conducive to on-the-fly adjustment. This combination may be something racers in particular will want to note. 

Construction/Durability
While we didn’t test long enough to really judge the shoe’s durability, based on testing dozens of shoes, these feel sturdy and well put together. The soft, supple synthetic upper is not too stiff, like some mid-level shoes. And there’s just enough mesh to vent without sacrificing toughness. The Boa dial is a bit larger and more substantial than the higher end models, which also means better durability – although having to unclip every time you need to loosen, rather than just dialing backwards, adds wear to the mechanism, and I’ve seen these wear out over time. But the cables and plastic guides should easily last the life of the shoe.

Drainage/Breathability
The 100’s feature a well-perforated upper, including two mesh openings over the toe – as well as two under the toes and a long one under the heel/midfoot in the outsole. Furthermore, the tongue padding is full of large holes, and wrapped in mesh. The combination means excellent breathability and drainage all around. There could be a bit more perforation on the sides of the midfoot.