Helmet with peaks

Fashion? Aerodynamics? Weight? Take your pick.

I read somewhere (I think it might have been the MET website?) that the peaks were on mountain bike helmets to prevent errant branches and twigs from getting in riders' faces.

Ah, it was on the Met site after all:

Quoted post said:

What is the difference between a road and a MTB helmet?

One main difference is given by the riding conditions. Off the road you are a lot more likely to have to deal with mud and tree branches for instance. A peak is found on all MET MTB models because it will protect your face against mud projection from riders in front of you and will also help keep branches away from your eyes.

Another big difference is how the ventilation works. On our road helmets most vents are located at the front of the shell, to grab as much air as possible, with big air exhausts at the back of the shell and crossed air channels inside. Few holes on the top of the shell (because the speed on the road guarantee a good ventilation through the helmet), keep the helmet very aerodynamic. On our MTB helmets, the top of the shell is a lot more perforated. This enables the heat coming out of your head to go up by itself (hot air is lighter) and exit the helmet even when the speed is too low to have any air travelling through the helmet.

I think its bcoz you have to crane your head to really see the road when you have the visor on, mountainbike has more upright positions while roadbike has really low positions, I dun use the visor on my roadbike bcoz of this reason ...

MTB it keeps the branches out of your eyes but on the road it obstructs your vision .

Ditto on the lack of vision with a visor. Otherwise most (all?) visors on MTB helmets are removable so voila! instant road helmet!