The Blackbird Send Aluminum rims are designed to eliminate pinch flats and keep the tire sealed no matter what you hit. We offer two versions. The Send 1 and 2 rim share a unique hollow box-section beadwall that creates a broad contact point with the tire, which is much stronger and doesn't slice tire sidewalls. The Burlier version, the Send II, adds a pair of ribs directly beneath the bead seat to keep them round after even the hardest hits.