A snug bike helmet fit is key if the helmet is to do the job of protecting you in an accident. Like sneakers, helmets are made on different molds that vary among brands. Unlike shoes, though, there are no standard "measurements" in helmet sizing. Most helmets list a measurement of the head circumference it will fit. This can help narrow the options, but your head might be a medium from one maker and a small from another.
Most of the models we tested come in a single "universal" shell size while other adult bike helmets, including the top-rated Scott Arx Plus ($125) come in multiple sizes. The goal is to find the helmet that fits your specific head shape as closely as possible and requires few if any pads to achieve a snug fit. The best way to do this is to go to a bicycle shop and try on different brands and different helmets within brands. "Try on the size you think you need, and then try a size smaller," says Rich Handel, Consumer Reports' assistant test project leader. (Warning: Don't be tempted to buy a larger size for your child, thinking she will grow into it!) If you wear a hat under your helmet, or put your hair in a ponytail, make sure your head is ride-ready before you go helmet shopping. If you're buying a bike helmet online, check the return policy to make sure you can exchange it.
If you ride a comfort bike or a cruiser that puts you in an upright position, you might be fine with a less-expensive mid-weight helmet. If you ride a racing bike with dropped handlebars in an aerodynamic position, consider a lightweight model that may decrease the strain on your neck muscles during day-long rides at high speeds. Another factor that's especially important to performance riders is ventilation—rated by our testers at 20 mph on a mo