Road helmets are designed for road cycling. They feature an elongated, aerodynamic shape and plenty of venting. These are lightweight helmets designed to offer protection while limiting weight and resistance. They will work for all types of cyclists. As with nearly every other helmet on this list, road helmets in the United States must meet safety standards designated by the Consumer Products Safety Commission (CSPC).
These models are similar to road helmets, but are more rounded and less expensive. They're designed as an inexpensive means of protecting your head and are a good option for the standard bicycle commuter or casual rider that doesn't want to spend the money on fancy designs and excess venting. They offer a simple, no-frills form of protection.
Mountain Bike Helmets
Though the average mountain bike helmet worn by cross country riders meets identical safety standards of the road or sport helmet, it provides a little bit of enhanced protection in the rear, since mountain biking typically involves increased dangers that aren't associated with road cycling or commuting. Mountain bike helmets usually contain a visor and more advanced fit systems to provide a snug, customized fit that isn't subject to a lot of sliding around due to vibrations from the terrain.
Downhill Mountain Bike Helmets
Looking more like motorcycle helmets, downhill mountain bike helmets offer full face coverage, using a chin bar on the bottom. They usually have plenty of venting. Since downhill mountain biking is inherently more dangerous than cross country and recreational biking, these helmets are designed to meet tougher safety standards and use the ASTM F1952 standard as a guideline.
BMX helmets provide enhanced protection and come in both cap and full face varieties. They are designed to protect more around the back and sides of the head. Dome-shaped cap helmets are often designed to be multi-sport and should be dual certified, for both the CPSC standard of a bike helmet and the ASTM F 1492 skateboarding standard. Similar to a downhill mountain bike helmet, full-face BMX helmets offer full face protection and a chin bar on bottom. These helmets often include a visor attached to the top and may meet the ASTM F 2032 BMX bicycle or the stricter DOT motorcycle helmet standard. BMX helmets have little to no venting since BMX competitions are quicker than others.