If there is a mountain biker in your family, here are some ideas that will make them happy on Christmas. Clockwise from top left, A balance bike to help the youngest rider get comfortable on a bike; A cold-weather hat to keep his or her head warm;  Gels or energy bars so the rider doesn’t bonk on a ride; Gloves to ensure they can shift and brake in cold weather; Gift certificates to a bike store if you can’t decide what to ge; A bike light so those diehard riders can see in the early dusk; Leg warmers to keep the exposed legs warm without creating too much drag; Socks to stand out and keep the bikers’ feet warm.