Shimano S-Phyre SH-RC903 Review

The updated S-Phyre RC903 features a revised fit, new routing for the front BOA cable, and slightly reduced weight. It is a leader in comfort and power transfer, excelling in all aspects of our in-depth testing. Below, we dig into what design and performance attributes make the RC903 such a great shoe.

Performance Comparison

Comfort

Ergonomic design, excellent adjustability, and top-end materials establish the RC903 as the leader of the pack when it comes to comfort. Previous iterations were single-mindedly focused on performance, and with a number of stage wins at cycling's Grand Tours, that recipe paid off. But with the RC903 edition of the S-Phyre line, comfort considerations no longer come in second.

The two halves of the upper are held together with two BOA Li2 dials. This top-of-the-line BOA system is easy to micro-adjust while riding and easily releases all tension when it comes time to slip the shoe off. Putting the shoe on, however, can be a little bit fussy, as the rear BOA cable readily snags on the front dial. Having the rear BOA dial mounted to the instep strap means that the strap flops around a bit while putting the shoes on, which is more annoying than inconvenient.

Gone are the plastic guides for the front BOA system, replaced with cloth guides that don't impinge on the toe box at all. Re-routing the cable also added another criss-cross, spreading the force of the closure over a larger portion of the toe box, allowing for more adjustment in the toes. Want to cinch the shoe down for an all-out effort? Just turn that front dial a bit to all but eliminate movement in the toe box. Want to cruise the next 40 miles home nice and easy? Dial the BOA back and enjoy stability without the pressure points.

Instead of having the two sides of the upper fold over each other, Shimano uses a tongue-less design on their shoes that allows for greater adjustability and helps spread forces from the BOA closure system more evenly across the top of the foot. The RC903 is also available in a wide version, which uses a wider carbon outsole, not just a higher volume upper. That said, it is still a performance-focused shoe with a narrow-fitting toe box. Even though this shoe is surprisingly adjustable for its last, there are other shoes in our lineup that will better accommodate higher volume feet.

Power Transfer

This is an area in which the RC903 truly excels. The carbon fiber outsole is one of the stiffest that we tested, the heel retention is tight, and the upper feels totally locked in. Shimano gives the RC903 their stiffest sole rating – a score of 12. Unfortunately, they don't say what that stiffness rating of '12' means in the real world. So we developed a sole deflection test to objectively rank outsole stiffness.

Our test involves bolting the shoe to a jig, setting up a linear deflection gauge, placing a heel block inside the shoe, clamping a U-bolt around the sole, and hanging a 25-pound weight from the U-bolt. The heel block locates the U-bolt over the ankle opening of the shoe, so that force is applied in the same plane as it would be by a foot. Measurements were taken three times, and the results were averaged to give us one sole deflection value.

The RC903 sole deflected only 1.39 millimeters, less than many other shoes we tested. This sole stiffness is just as apparent out on the road, translating to a very secure connection to the pedals. While a sole this stiff pushes nearly every watt to the pedals, it also can cause some foot fatigue. We noticed the soles of our feet starting to ache after a number of hours of riding with the shoes snug. Loosening the closure can alleviate that feeling a bit, but it's still more noticeable than some of the softer shoes we tested.

Shimano also remodeled the heel cup on the RC903 with this update. They eliminated the rubber heel retention pads from the RC902 and lined the collar with a rubberized, synthetic fabric that extends down into the heel cup. The heel cup is very stiff, with padding in all the right places around the Achilles tendon to lock your heel in place. The result is an extremely secure fit – we never noticed our heels slipping during hard efforts or even while walking around. This fit encourages you to engage your hamstrings and pull through for a more even pedaling stroke. The additional heel support also seemed to help keep our knees aligned, reducing how much our feet would twist in the shoes.

The revamped RC903 now uses a one-piece upper made from microfiber synthetic leather. While supple and foot-conforming, the upper doesn't stretch or flex during hard efforts, nor does it crumple or wrinkle when tightened down.

Durability

The S-Phyre RC903 has all of the right ingredients to make it a long-lasting shoe. Designers opted for durable materials, and the shoe incorporates replaceable parts in certain high-wear areas. The heel is fully enclosed in a plastic cap, the front part of the carbon outsole is surrounded by a plastic ring, and there is a raised toe pad that protects the front tip of the sole. Perhaps the only downside is that it might not look as sleek after all of those years of service.

The microfiber synthetic leather upper is tough and unlikely to tear from regular use while riding. However, the upper wraps fully around to meet itself under the sole, which exposes it to scrapes from walking around. The plastic heel cup also scratches easily, and the black color of the underlying plastic shows through the blue heel cup paint. Functionally, there aren't problems. But it's important to point out that the otherwise durable RC903 shows cosmetic damage more quickly than other shoes we tested.

High-use components like the BOA dials and heel pad are replaceable, which is very important for the longevity of a premium shoe like the RC903. The dials are also covered by BOA's lifetime guarantee – you can replace them at no charge, with only a few questions asked. If you'd rather avoid the questions, you can also purchase replacement dials, which are super easy to install. The same goes for the rubber heel pad, which is sure to wear out after years of starting and stopping and walking around at cafes. It's held in place by only one bolt, making it an easy fix.

We wish that the RC903 featured a replaceable front toe pad, which is an area that wears down from pushing off to start riding. Not many brands offer this as a replaceable pad, so it's understandable that Shimano also does not. But it's a feature that we'd love to see them add to future shoes in the S-Phyre line.

Weight

As you would expect from a high-performance road cycling shoe, the RC903 is superlight, coming in at 16.72 ounces (474 grams per pair, or 237 grams per shoe) for a pair of EU size 42.5. Although it is still a lightweight shoe, the main goal of the RC903 is certainly not shaving grams.

The one-piece upper has very thin padding on the inner layer and mostly bonded connections between materials. The RC903 also does away with two plastic cable guides of the R902 and features a lighter outsole. There are lighter shoes on the market, but the RC903 still manages to include an external plastic heel cup and plenty of rubber protection on the outsole to ensure proper foot support and durability.

Should You Buy the Shimano S-Phyre SH-RC903?

The S-Phyre SH-RC903 is one of the stiffest and most performance-oriented road shoes out there. It provides unparalleled heel retention and power transfer, making it the perfect companion for riders looking to maximize their performance during hard efforts. The toe box is on the narrow side, but if that works for your foot, then it is just as well suited to all-day rides. We don't deny that it's expensive, but if you're looking for a premium cycling shoe that is built to last, the RC903 is worth the investment.

What Other Cycling Shoes Should You Consider?