Rock Shox Bo XXer Upper Tube Upgrade Kit Old Meets New. Butter Wagon Tech for You If you're running a Rock Shox 38mm Bo XXer D1 and want to match the front-wheel grip that D2 riders enjoy, the Rock Shox Bo XXer Upper Tube Upgrade Kit is the perfect solution. These upgraded stanchions bring Butter Wagon Tech (BWT) performance to your existing chassis. The technology features a matrix of precision-machined divots that carry fresh, high-density Maxima oil to the bushings with every millimeter of travel, ensuring consistent lubrication throughout your ride. Additionally, the stanchions include strategically placed breather holes that allow lower leg air volume to increase during compression, effectively decreasing breakaway force and improving sensitivity. Because the SRAM Bo XXer Upper Tube Upgrade Kit is fully compatible with both D1 and D2 platforms, it drops straight into your existing lowers, delivering a more supple feel and predictable tracking without the need for a complete platform swap. Butter Wagon Tech stanchions use a proprietary pattern of divots to pull Maxima oil up to the bushings on every stroke, keeping friction low across the full service interval Stanchion breather holes equalize air pressure between the lower leg and the seal head, reducing breakaway force and keeping the fork sensitive throughout travel rather than ramping up unpredictably at speed Complete kit contents include right and left Butter Wagon Tech upper tubes, bump stops, oil, and bolts so you have everything needed for a full installation38mm Bo XXer D1 (2024+) compatibility means this is a direct drop-in upgrade for your existing chassis with no lower leg swap required | Sram | Rockshox Boxxer Upper Tube Upgrade Kit Upper Tubes