Cycling shoes are generally designed with airflow in mind - ie they allow air to pass through them quite easily and cool your feet... Of course that's bad if it's REALLY REALLY REALLY REALLY cold outside... so the booties can block up the vents in your shoes... depending on what type you get, can provide some bulk for insulation purposes and also keep your feet a bit more dry.....
In Canberra you NEED them in winter or you feet freeze. Mind you, in saying that, sometimes, even when I am wearing them my feet still freeze. Its just bloody cold at -8. And at -8 and 30 kmph, the windchill factor is about -20 or more.
Plus as mentioned above, many of the bike shoes are just mesh. The overboots block out some of the wind from blowing straight through the shoe.
The neoprene (wet suit) booties I own don't actually keep all the wet out (I think it leaks in the top as much as anything). However, the insulating qualities are great for cold days.
I rode one weekend where we were riding in rain and hail through mud and puddles (new brake blocks on Monday due to all the grit!) and feet and booties got soaked. Still wet on Sunday morning so I left them off but, 20km down the road my cold feet persuaded me to add something - anything - for warmth. The cold booties soon warmed, kept the draughts out and trapped a nice warm layer around my toes. Comfy all the way home even though I never did completely dry out!
Murray wrote:The cold booties soon warmed, kept the draughts out and trapped a nice warm layer around my toes. Comfy all the way home even though I never did completely dry out!
Keeping the wind out and the warmth in is far more important than staying dry.
You're going to get wet. Whether it's raining or not you will get wet 'cause you'll sweat. Not a lot you can do about that. Windproofs with good ventalation and thermal layers are far more useful than a water proof.
That's not to say a rain jacket doesn't have its place. In torrential rain I use one as it makes the impact on the skin more bearable. I'm under no illusions about a rain jacket keeping me dry though.
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