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Reviewed: Giro Prolight SLX Shoes

Dancing shoes. It’s an irony lost on no one that cycling shoes make you as graceful on the bike as they make you awkward off. For most of the sport’s history, cycling shoes have more resembled ballet slippers than the industrial hybrids they generally are today. They looked small and flimsy, and pretty much felt that way, though worlds better than riding in sneakers. Our first few pair of cycling shoes was the Detto Pietro Art. 74 a bargain-basement shoe that boasted a thin nylon sole, a thin cleat, a thin leather upper that looked like it was perforated with a hole punch, and leather laces. Despite all its flaws, it fit a niche, and the shoe lasted, almost unchanged from the 1970s into the 1990s. Detto Pietro even added three-hole mounting bolts toward the end of the shoe’s run.

The Giro Prolight SLXs, with their matte Black sole, largely matte Black upper, and few decorative elements took us back to those old shoes. The only flourishes are the reflective “G” on the outside of the toes, on the heel, and little reflective dots atop the toes. The lack of embellishment was surprising, as most top-tier shoes advertise their status with lots of logos, flashy colors, and a unique binding system. More than one friend commented that they reminded him of the old Art. 74s.

Don’t let the appearance fool you. The shoe is really high-tech. First and foremost, we give credit to the sole. It’s the foundation of the shoe, and if it is thick or flexy, or curved poorly, the rest of the shoe, no matter how pretty or well it fits, is worthless. This sole is really thin. We measured through the bolt holes in the shoe to the lasting board (the board that your insole rests on). It’s 5mm at the front hole and 5.2mm at the back holes. Giro states the sole thickness is 6.5mm, so we’re guessing that their overall measurement is about right. In comparison, our current shoes are 2.5mm thicker in the same places. For many, it’s probably a good idea to drop your saddle height 2.5-3mm when switching to Giro shoes, unless you’re already riding super-thin soles. Still, despite the lack of bulk, the EC90 SLX sole feels as stiff as any shoe we’ve had when we pedal. Interestingly, when walking on the shoes, the toes seem to flex a bit more than in our current shoes. The sole has a matte finish that continues the understated style; it also makes scuffs seem less obvious than they would be on a shiny carbon-weave finish. The heel and toe pads are sleek, fit in with the curves of the sole, and look good whether seen from the front, the side, or back.

The upper not only looks soft, but feels soft and pliable both on the inside, where it is lined, and on the outside, where the micro fiber is finished in two different ways and finely perforated as well.

The heel cup is firm and padded, and the tongue is padded and notched. For the insole, they offer two options, super light, wafer-thin insoles and adjustable, supportive insoles (the SuperNatural Fit Kit). The super lights weigh 12g apiece. This is the insole that we typically find in high-end Italian shoes. The adjustable insoles weigh 20g for the base, and then up to 9g for the arch supports. These insoles are aimed at people who buy supportive aftermarket insoles.

And, as a nice perk, they include an over-the-shoulder shoe bag. It’s big enough for some clothes as well, though its value is in protecting other stuff in your travel bag from dirty shoes and cleats; not wet shoes, as the sides are mesh.

We sized ourselves as fitting Giro’s 44.5 shoe. This is the size we take in DMT, Sidi, and Specialized. With the wafer-thin insoles, the shoes feel a bit loose until we tighten the straps. But with our arch height and foot issues, there’s no way we’re going to ride the wafers. With the SuperNaturals, we knew we were going to put in the highest arch. Once these were installed, the shoe felt just about right, as if we were close to the limit of the shoes in terms of length and width. The Supernaturals also resulted in a nice soft lock on our heel.

Giro boasts about how light these shoes are. They are indeed incredibly light. The left shoe weighed in at 217g without any insole, and the right weighed in at 210g. Put in their SuperNatural insoles, and the left was 247g and the right 238g.

Next, we focused on the cleat. We’re Speedplay users, so the included bolts were not recommended for use; try them if you ride Look, Shimano, or Time. Because of the thin sole, Giro puts inshortened nuts; thus the need for shorter bolts when using some cleats. We lubed the Speedplay bolts with Blue Loc-Tite; lubes and locks. The stock snap-shims of the Speedplay cleats seem to fit the curve of the sole perfectly.

When putting on the shoes, we start with the middle strap, get that down, adjust the tongue so the notch is close to our tendon, then lock down the top. The bottom strap, the one above the ball of the foot, functioned pretty much as a “set and forget” strap. We got it close on the first or second wearing and left it in place except when pulling out the insoles and washing the shoes.

That middle strap seems to do a great job of evenly pulling the inside area of the shoe around our feet. The top strap feels short, but it pulls easily and stays in place. Aesthetically, we love how the straps are arrayed diagonally across the tops of our feet.

Our first surprise was in positioning the cleats. Since our current shoes have the cleats pretty close the rearward limit of travel (as in the cleat is pushed back relative to the toe and the three bolts), we set up the new cleats in this position. After ten minutes of riding in this position, we found out this was wrong; our calves weren’t engaging as we trained them to. Turns out Giro bench-marked the competition, consulted with ReTul and moved the cleat-mounting nuts back relative to where they used to typically go. This makes getting to the currently en vogue behind the ball of the foot cleat position easier. For us, the result was the cleat needed to be placed forward of the middle of its travel range. A good tip we used to get our cleats in the ballpark of our preferred position was measure from the edge of the heel to the rear edge of the cleat on our current shoes. Then take that measurement and use it to set up the cleat on the new shoes.

Giro, in one of the many small touches they did very well, created a great grid system for lining up cleats. There are alternating red and white lines as well as numbers. They make it pretty easy to line up cleats as well as adjust them. The lines seem to be 2mm apart, so it’s easy to adjust your cleats in very small increments.

After riding the SuperNatural insoles a bit, we decided to install our custom foot beds. The arches on the superNaturals aren’t tall enough for our arches and as such, we didn’t feel our knee was as stable as we like on the down stroke and our feet moved around a bit inside the shoes. This was livable for short rides, but we’ve found long ones can lead to problems.

And the insole swaps lead to our second surprise. Our custom insoles raised our heels in the shoes to the point that they didn’t feel locked down. Not a great feeling as the sides of the cup seemed to be squeezing the bottom of our feet as opposed to holding our heels down. Turns out that Giro designed the heel pocket to work with 4mm thick foot beds or thinner. This means ours is probably a few mm taller. A call to eSoles yielded a potential solution. Esoles can “adjust” their custom insoles in cases like this. It means they probably grind off a bit of the edge to the heel cup they built into their insoles. Send in the custom insoles along with the stock insoles so they have a reference, and they can make the adjustment. Other custom foot bed providers can probably do the same.

We went about riding them. The uppers feel “broken-in” pretty much out of the box as they conformed to our feet very well from the moment they were on. The Velcro held firm, despite not feeling like it was really locked into place like a buckle system does. We did four-hour rides and didn’t feel the need to adjust the straps once. The lack of weight we noticed right away, but the sensation disappeared over a few rides.

Rain is just another riding condition. Some shoes take a long time to dry, and with the padded sock liner around the heel, we expected the Prolights would land on the extended side of drying time. Don’t know what they used for padding and what the polyester material is for the liner’s exterior, but it didn’t seem to absorb water and dried very fast. So, too the tongue. Overall, the shoes dried very quickly, even on humid days. And the exterior cleans up pretty easily, though the shoes are Black.

There are, after this spell, only two things that we think they could do better. One is make the exterior heel pads taller. Aesthetically, they work, but practically, they’re a bit short for our walking habits (we do a fair amount of walking in our cycling shoes) and there are lots of scuffs on the sole just beyond where the heel pads end. The second is the heel cup; it isn’t deep enough for our insoles. Having our heel not feel snug inside the cup was fine when we were below threshold and even sprinting. But doing VO2 Max intervals, we didn’t feel like we could push hard enough. We’re probably going to get our insoles ground down a bit, but it’s an adjustment that could make using these insoles elsewhere much harder.

With over a month of ride time in these shoes, we’re still very impressed with the Giro Prolight SLX. They work very well, an incredible freshman effort.