Universal size? That doesn't sound like a good idea. That'd be almost as bad as ordering a universal size shoe. It's probably either for kids, or it's really big and comes with a lot of padding to fill the gap. That'll move around a lot in a crash.
You should be able to shake your head around and have the helmet barely move, if at all.
Also- like shoes, it's not just about size, it's about shape. Everyone has a different shaped head, and every company uses different shape molds...often several different molds depending on the helmet. The Bell Influx and Varient fit me perfect in a large. The large Bell x-ray is terribly tight and uncomfortable in a large. Most Giro bike helmets are either uncomfortable or too big, but their Fuse ski helmet is perfect. I've learned the hard way not to buy a helmet I haven't tried on.
You can get pretty nice bike helmets, in sizes, for under $50. I ride a $5k bike, but this $50 helmet served me well for years...
http://www.pricepoint.com/detail/201...p=215%20BELIN0
jensonusa is another great place to buy stuff online.
Here's my mean machine. Just did a nice night-ride last night...
