Fenders make cycling in wet and cold conditions tremendously more comfortable. They prevent most of the water from the road from hitting you in the face (front fender) and butt (rear fender). More importantly though, fenders keep crap off of your drivetrain . . . and a cleaner drivetrain means that things (chain, cassette, front and rear derailleurs) last longer.
I have a simple mountain bike, would fenders work on those? I usually see them on city bikes...
As long as you have eyelets to screw fenders on to at the front fork and near where the rear hub is it should be doable to put fenders on a mountain bike. Planet Bike makes the Cascadia II ATB fenders which I used with no problem on an older mountain bike that I used to have.
If you have a full suspension it may be trickier to install the fenders. Take a look at these install instructions and then look at your bike to make sure that they'll fit properly:
http://planetbike.com/files/Hardcore-inst%282013%29.pdfMy ride is about 9 km (5.6 miles) each way.
On a regular dry day, it takes me a bit under 40 min., but I don't know what to expect in the colder/wetter days.
We don't get anything near Canadian winters over here - temperatures average around 8-17 C (46-63 F). I guess a really cold day would be around 2 degrees C (35 F).
But again, I hate being cold.
OK, it sounds like you're going along at a pretty moderate pace so you won't have to worry so much about overheating. If it never gets below freezing, you should have quite a comfortable commute year round.
Here's the gear I'd recommend:
Cheapest/Most Versatile Winter Wear:
Track pants (the kind with a somewhat wind blocking shell) - you probably already have these. Just get an elastic band or something to tie the cuff of your pants close to your ankle so it doesn't catch on your chain and rip your pants.
Wool or Fleece sweater - you probably already have one of these
Windbreaker jacket - you probably already have one of these
Waterproof/insulated hiking boots - Get boots that fit slightly larger than you normally would buy . . . having extra room in your boot means you get better blood flow so your toes don't get as cold. Waterproof boots means your toes don't get as cold.
More Expensive Bike Specific Winter Wear (tight fit means you go faster for less effort, light weight, tends to breath better):
Arm warmers - I'm partial to DeFeet's wool Armskins arm warmers
Fleece jogging tights - Any decent jogging tights will keep you warm down to about 8 degrees, just put them over your cycling shorts. I just pick up any that are on sale and seem to fit OK.
Long underwear - An extra layer of long underwear over your cycling shorts and under your jogging tights will keep you warm down to about freezing.
A long sleeve fleece cycling jersey
A tight fitting long sleeve cycling windshell - I'm very happy with a Castelli Velo jacket for this (although I wish it had a rear pocket).
It's totally worth getting a couple buffs (
http://www.buffwear.com/buff-adult-headwear/original-buff). You don't have to get that specific brand, any of the cheaper knock-offs seem to work well too. You can use one as a scarf/face covering and one as a hat when it gets cold, and they weigh almost nothing so you can always keep them in your bag in case you get caught out in the cold and need to add something right away.
For gloves, I like to get two pairs of long fingered soft shell jogging gloves. Get one pair that fits you well and one pair that's a size or two larger so you can put it over your gloved hands when it gets really cold. That works for me to below freezing. The ones I'm currently using are these:
https://www.amazon.com/Head-Multi-Sport-Running-Gloves-SENSATEC/dp/B014TNQU3Y/ref=pd_day0_200_1?ie=UTF8&pd_rd_i=B014TNQU3Y&pd_rd_r=W4PGX5ZPESM0RV5G16EF&pd_rd_w=5Zv6H&pd_rd_wg=rO3rh&refRID=W4PGX5ZPESM0RV5G16EF but I'm sure any similar jogging glove would work great too.
Get wool socks. They stay warm when wet, (unlike cotton socks) and aren't usually too expensive. I use these when it gets really cold (
http://www.walmart.ca/en/ip/mens-wool-crew-socks-6-pairs/6000110751942), but any heavy weight wool socks will work fine.
And what about shoes? I hate to think of my sneakers getting soaked and my feet getting cold.
I'm also going to need my shoes to ride back, so if they get wet they probably won't dry by the time I leave.
Waterproof insulated hiking boots are awesome for winter commuting! In a pinch you can always wrap a plastic bread bag around your shoes and then hold it in place with rubber bands, and it works OK . . . but you'll shred the bag by the end of a ride. Better to get the boots. I like a low cut boot that doesn't go much past your ankles because they feel more comfortable to pedal in.