With WIDE ANGLE™ rim design providing superior stability, the SRAM RAIL 40 29er UST Boost rear wheel can withstand the most aggressive All-Mountain / Enduro riding by setting a new benchmark for stiffness in its category. Featuring the perfect balance of strength, lightweight and width for enduro terrain, RAIL 40 delivers high performance ride quality all the way down.
- Lightweight but strong UST Tubeless compatible aluminium rim, asymmetrical profile with TAPER CORE™ technology. Welded joint
- WIDE ANGLE™ rim profile (23mm internal width)
- SOLO SPOKE™ double butted spokes
- Rear hub feat. DOUBLE TIME™ ratchet mechanism for durable, quick engagement
- hubset equipped with SPEEDBALL™ bearings
- BOOST 148 compatible (12x148mm thru axle)
With revolutionary advancements in bicycle componentry, like SRAM’s XX1, X01 and X1 drivetrains, mountain bike designers have been given almost limitless freedom to focus solely on the performance of the bike. Each advancement demands that the entire package works flawlessly. Aggressive trail and enduro riders have been increasingly enjoying the benefits of larger wheels, but many still view 27.5" and 29" wheels as a possible weak link. Which is why SRAM has developed an open standard with Boost compatible components for SRAM drivetrain, hubs and RockShox forks.
DOUBLE TIME™ Freehub
Ratcheting up the smarts. This straight-aligned, 4-pawl design turns the 26-tooth ratchet ring into 52 points of contact. The result: smooth 6.9-degree engagement without reducing tooth size or offsetting internal geometry—which means serious long-term durability.
With SOLO SPOKE, you’re never wrong. SRAM wheel design eliminates the need for different spoke lengths—one size fits the entire wheel. This identical-length design means no longer wondering whether you have the right front/rear/drive-side/nondrive-side spoke handy. Front + Rear + Drive-Side + Nondrive-Side = 1 Spoke.
SPEEDBALL™ - Bearings
The only adjustment they’ll ever need was made back at the factory. Every part of the ball bearing comes from the exact same supplier—which means that each bearing bore can be precision machined to fit the bearing race exactly. With tolerances this tight, the days of adjusting play after every ride are over.
TAPER CORE™ - Rim
Strong in the right places. The sidewalls of SRAM rims are reinforced along the wings to withstand major impact. But the sidewalls then taper in along the center—reducing overall mass. The result is a very light rim with excellent dent resistance.