SRAM tout the S40 as the most versatile of their 'new' three-model alloy-and-carbon road clincher range (they're essentially reworked Flashpoints from recent acquisition Zipp) and at least in theory, they are.
The S40s are the lightest in the range and the 40mm-deep rims sport Zipp's slippery hybrid toroidal cross-section for notably good high-speed cruising on the flats but without the nasty crosswind handling that can often plague deeper rims.
The alloy cartridge bearing-equipped hubs spin smoothly too, and the fat, bladed stainless steel spokes and stout rims (with structural, not just aerodynamic, co-moulded carbon caps) make for minimal wind-up or lateral flex when hammering out of the saddle.
However, 'lightest in the range' still equates to a ho-hum 1,802g for the pair (814g front, 988g rear, plus 90g for skewers) – nearly 100g more than claimed and heavier than one would expect given the shallow rim depth and price tag.
The rear wheel's commendable stiffness and reasonable 500g approximate rim weight make up for this somewhat but there's still little masking the extra mass when headed up steep pitches or trying to make big accelerations.
Compared to some more competitive options, an S40 rider would be lugging an extra 400g around (nearly a full pound) – more than enough to ward off even the staunchest 'wheel weight doesn't matter' pundit.
Those stiff rims make for a pretty rough ride, too, and to add insult to injury, our wheels were out of true right out of the box (a supposed early production problem which SRAM road PR manager Michael Zellman says has since been resolved).
Moreover, the hidden nipples require tyre, tube and rim strip removal for access. A grabby textured finish and nylon washers on the included skewers make it hard to generate a lot of clamping force, and the sharp edges on the levers are rough on the hands.
Fancy rim aerodynamics aside, there are simply too many other better options out there to make the SRAM S40 a recommended option, including SRAM's own all-aluminium S30 AL Race, the HED Ardennes and the Mavic Ksyrium Elite ($650 cheaper and 250g lighter), to name a few.
Not to be forgotten, either, are good custom builders who should easily be able to craft a set that can meet or exceed the S40's performance attributes for less money. The SRAM S40 wheels aren't bad, but you can definitely do much better for the money.