I don't think I, personally, could buy one cold, online. Perhaps try one on in the shop then buy online if the deal is better. It would have to be a lot better though as, being a lazy bastard, if I found the one I liked in the shop, I'd just buy it. Same with boots.
I would find what fits best at a shop then look around. I've not bought a lid online before. Either at the shop or NEC bike show
You definitely need to try it on. Fit is the most important factor in choosing a helmet. While I can understand the temptation to try one on in a shop and then order more cheaply on line it's not really fair on the shop. You have got to ask what will we do when the shops all go bust and we can't find somewhere to try on a new helemt.
Most shops selling online cheap are the same people that turn up and sell at your big local markets etc, I have seen the way they load and unload their vans and I have seen them swaping display ones in and out of the boxes etc. Yes you don't know what happens in the stock room at the shops but I think they are alot more professional with it. I personly would rather pay 10% more for something I know is 1 - genuine 2 - safe
I bought mine online after trying the same helmet on in the shop but to be honest I'd probably be more likely to just buy in store now. At the end of the day I felt a bit crap after I'd got a better deal online because the guy in Hein Gericke straight away spotted that I needed a long oval helmet and knew exactly which lid to fit me with. I think it's worth paying the bit extra for the advice and being able to actually try them on. I'm kinda in the market for a new one at the moment and went trying some on the other day and was quite amazed by just how bad some of them felt on. Literally like sticking a rugby ball into a bucket. Space in all the wrong places.
+1 what Ken and Rich said. A good fitting helmet is the most important investment you can make, I am not that bothered about what it looks like (other than has to be plain white) as long as it fits me well and has plenty of ventilation and air flow. I know from history that Shoei suits me. But when I brought a new one last year I tried on dozens of makes and models and listened to the advice given. The guy at Infinity Motorcycles in Holborn was brilliant and really knew his stuff. I thought it was worth paying a few pounds more for that service even if in the end I went for another Shoei, which incidentally was one of the lids he first recommended. I have also found that if you already know the online prices and ask they will mostly match it assuming the price gap is not that huge. If you don’t ask you don’t get. One other thing regarding helmets. I replaced mine because I dropped the old one, not far only from the bike seat onto the pavement, if your not sure of its integrity is time for it to go and to stop it finding its way into the food chain again I drilled a few holes in the top and knocked it in with a hammer.
Try it on unless your buying the same make as previous then if theirs a good deal it's worth a try!!!