With one quick look at the Giro Prolight SLX Shoes, you'll know something is different. There are no mechanical closures, a rarity among pro-level shoes. This is in response to the needs of their marquee rider, Levi Leipheimer. Being meticulous about his gear, he wanted Velcro closures rather than a buckle so he could be confident that the shoes would survive a crash; buckles can break and having one go in a Grand Tour is a lousy way to lose a race you prepared all year for.
Velcro, great. Simple, adjustable, conforms well to the foot, hard to break: everyone can get into that. But Giro didn't just drape three straps across the top of the shoe. They designed each strap to do something a bit different, so each is angled slightly differently. The top strap holds the heel into the cup, the middle strap goes across the metatarsals to anchor your foot in the shoe, and the bottom strap takes up any loose space in the forefoot. If you take a close look at the medial side of the shoe, you'll see that each strap is fixed on large swaths of material, meaning that you're pulling the entire upper over your foot, rather than creating pressure points under each strap. Another subtle but striking feature is the way the toe box is constructed. One-piece toes look great, but the smooth look often comes at the price of limited adjustability. On the Prolight, the toe area looks conventional, but it allows for a wide range of adjustment on that bottom strap and eliminates the dreaded pucker, even if you have a narrow forefoot.
And, because every gram counts when you're climbing 15,000 feet a day, several days in a row, Leipheimer also wanted the lightest possible shoe without losing either stiffness or security. This Easton EC90SLX is the lightest and stiffest sole Giro uses in their shoes. Easton and Giro are divisions of the same company and Giro leaned on Easton engineers here. The result is a super-stiff sole that's only 6.5mm thick over the pedal, and thanks to the lay-up and titanium bits, it's super-light. Each sole is weighed after being molded. If it weighs too much, it's rejected. That means the sole in a size 42 has to weigh within three grams of the target 60g. 63.1g and the sole isn't built into a Prolight SLX.
Every part of the Prolight shoe gets this kind of scrutiny. The upper is soft, super-thin Teijin AG100 ultra-light microfiber that Giro worked with Teijin to develop. It's only 1.1mm thick, allowing it to conform easily to your feet, but it also doesn't stretch, thanks to an ultra-thin internal webbing that's bonded behind the microfiber exterior. The shoes would miss the mark if they weren't breathable, and though it has a smooth finish, it breathes well enough to stay comfortable on summer days. Inside the shoe, there are very few seams, and a layer of polyester liner material eliminates any possibility of chafing.
The tongue is generously-padded, with equally generous perforations in both the foam and the Teijin covering to make sure your foot breathes. The top of the tongue is notched so your tendon doesn't find any resistance through your pedal stroke. Fit tip: when putting on the shoes, align the split in the tongue with your tendons.
Continuing their pursuit of super-lightweight race shoe, the D-rings that you use to pull the straps are made of titanium. The overall weight of a size 42 shoe is 205g, among the lightest on the market.
As we wrote above, the shoe looks different. Another difference is that there seems to be very little architecture going on around the heel. This is by design. Looking at the increasingly-complicated heel cups on some of the competition, Giro decided they'd rather the shoe fit well everywhere and that careful construction and quality control would produce the desired fit and consistent dimensions in every shoe.
Another benefit of a less-constructed heel cup is that there is more room for inserting after-market insoles. Giro includes two sets of insoles with the Prolight SLX -- an ultra-thin, ultra-light EPP footbed for people who want to keep weight to a minimum and don't need support, and their SuperNatural Fit Kit for those who need arch support. If you don't know which kind your foot prefers, try both. But, back to the point of the simpler construction, this upper is designed with the idea that people might well use a custom insole. To this end, they rejected the "bathtub" style sole, the ones that curl up on the sides, and went with a flat, neutral sole that would better accommodate different insoles and a larger range of foot widths.
Giro's SuperNatural Fit Kit is Giro's aftermarket insole solution. They made them as thin as possible at the heel and ball of the feet so you don't feel like you're foot is being lifted out of the shoe by the insole. The base material is EVA foam, so you'll crush the insole where your foot pushes against it, or "set" it if you want to get technical, over the course of several rides. The top is finished with a thin layer of X-Static material for its wicking and anti-microbial qualities. But what makes the SuperNatural Fit Kit a big deal is that the insoles come with three different height arches that allow you to customize the arch fit.
The Giro Prolight SLX comes in two colors -- Black and White. They're available in whole sizes from 39-48 and half sizes from 39.5 to 46.5. The sole is drilled for three-bolt cleats. There are pads underneath both the heel and toe for walking on slick surfaces. A travel bag is included with the shoes.
For shoes I value lightness, stiffness, and a no fuss fitting system. These shoes equal or exceed all other shoes I have owned on the first two criteria (comparing with S-works, Octanes, and LGs ultralights). When it comes to fit this will be personal, but for me these are the most comfortable shoes I have owned, three quick velcro straps are secure with no pressure points. Definitely will be buying a second pair.