I have never understood the need for vests, dont your arms and hands get cold when you dont have sleeves?

My torso produces enough of its own heat, if anything I think I would want to wear sleeves and nothing else. Can someone please enlighten me as to why vests etc are so popular.

Cool summer mornings when you need just a bit of extra warmth on your torso to avoid being uncomfortable. If you want a bit of extra warmth, it is much more efficient to warm the torso than the limbs. The limbs then act like cooling fins on an air cooled engine and keep you from overheating.

If you were to just cover your limbs, the torso would start to cool and begin shutting off blood supply to the limbs.

I love fleece vests when skiing in the winter and a light wind vest for cycling in the summer.

For me they are for when i have jersey, arm warmers, don't yet need a jacket but want to keep a bit warmer.

your chest gets hit with the most moving air so it gets cold and pulls heat from everywhere else to stay warm.

notice on pro decents when they shove newspaper under their jersey for the ride down off mountains.. it's to keep their chest and core warm

ok then on the same note, I have seen winter jackets with lighter sleeves than the torse (lighter being less warm fabric) does this follow the same idea. Why wouldnt they just have normal sleeves?

I guess the idea is that it keeps your whole body a little bit cooler?

They have some jackets with removable sleeves to make it a vest if it warms up and you can pack the sleeves away.

shrug.. my jacket is all the same stuff i just unzip it a bit if i get too warm and zip it back up when i get colder

IME, the hardest part about cold-weather riding is overheating. It's easy to stay warm once I get going, but if I start to overheat it's really uncomfortable. Even on sub-zero nightrides in winter, I rarely use a full jacket for long. Vests are a good balance for me, especially layered with thermal jerseys.

My arms sweat in every nylon jacket I've worn while riding, thinner sleeves would reduce that. I prefer a vest when the temperature is colder as it shortens the time between feeling cold and then warm, as well as the cooling off time.