If you want to be absolutely sure that you'll have stopping power on your gravel bike when you're pedaling through thick mud or across unpredictably sandy singletrack, Shimano's BR-RS805/RS505 Flat Mount K04S Metallic Disc Brake Pad is what you'll want to have mounted to your frame. The rigid metal compound Shimano uses offers more longevity and delivers strong, responsive stopping power in extreme riding conditions compared to resin, and the K04S pads are compatible with Shimano's impressive all-new Ultegra BR-RS805 and 105-level BR-RS505 hydraulic disc brakes.