Zipp 303 XPLR S Rear Wheel The Zipp 303 XPLR S offers a significant speed upgrade for gravel riders without the high price tag. It incorporates key innovations from Zipp’s premium gravel wheelset, making it both affordable and durable for the discerning gravel cyclist. The 303 XPLR S is the fastest gravel wheel Zipp has ever developed, featuring a mega-wide rim that integrates seamlessly with approved gravel racing tyres. Unlike current gravel wheels, which are modified versions of road wheels focused on high stiffness and low weight, Zipp prioritises speed. Rolling resistance, vibration loss from rough surfaces, and wind are significant barriers in gravel riding. To tackle these challenges, Zipp applied its Total System Efficiency design philosophy specifically for gravel. The 303 XPLR S is designed with a new approach, starting with the ideal gravel tyre and building the wheel around it. Zipp’s engineers studied recent changes in gravel racing and made several key conclusions: 1. As gravel speeds increase, so does the importance of aerodynamic efficiency. 2. Current gravel wheels perform poorly aerodynamically with gravel tyres. 3. Low tyre pressures are essential for speed on gravel, but current rim designs don't support lateral cornering loads at these pressures. 4. Current gravel rim designs do not prevent pinch flats at low tyre pressures. Gravel racing tyre widths typically range from 38-50mm with varying tread patterns. Current gravel wheels have an external rim width of 28-30mm, which creates an aerodynamic mismatch with tyres over 40mm wide. This mismatch results in a less efficient airfoil cross-section. Zipp’s testing shows that the 303 XPLR S, with its efficient wheel and tyre pairing, provides a 5-watt aerodynamic advantage over a leading competitor. This wheel is optimised for use with the Goodyear XPLR Slick and Goodyear XPLR Inter tyres, both designed in partnership with Zipp. Low tyre pressures significantly increase speeds on gravel. However, a narrow tyre bed with low pressures can cause tyre collapse while cornering. The 303 XPLR S’s wide tyre bed increases tyre stance, allowing for lower pressures without squirming, decreasing vibration loss while maintaining control in corners and traction while climbing. The 303 XPLR S also reduces pinch flats with a rim edge that is 77% thicker than previous models, reducing damage when the tyre bottoms out on the rim edge. Regarding rim depth, conventional wisdom suggests shallow rims for gravel. However, many gravel courses now see speeds of 35kph+ (22MPH) with top speeds over 60kph (37MPH). The 54mm deep rim of the 303 XPLR S creates an effective aerodynamic complement for large gravel tyres at high speeds. Zipp’s research found that this depth provides the perfect aspect ratio for aerodynamic efficiency with a 40mm gravel tyre at race speeds. The 303 XPLR S is only compatible with approved tyres, specifically the Goodyear XPLR Slick and Goodyear XPLR Inter, which are designed and optimised for this wheelset.