The biggest difference between a road bike, a cyclo-cross bike and gravel bike is the frame and fork clearance for wider tyres, sometimes up to 55mm. Most road bikes max out at 28mm tyre clearance. The wider tyres can handle most surfaces you throw at it. The frame also has a more relaxed head angle, taller head-tubes for a more upright and comfortable position on the bike. The gravel bike has a longer wheelbase and a lower bottom bracket for better stability and cornering. The beauty of the gravel bike is their efficiency over distance on gravel roads as well as doubling up as a road bike. Two bikes in one!