You have observed two types of cyclists on the road. Some of them are wearing regular street clothes when cycling, and some wearing specialized bicycle clothes. Any how you need to wear a perfect suit when you are intended for cycling.  In fact never ride except in clothes made for this cycling purpose. However there are some principles in wearing such clothes. This is why you must think about it when dressing for cycling in most circumstances like weather or location.

If you will ride in Boulder County Colorado, the weather may fluctuate. The temperature of this place is 60’s in the morning and ends with temps in the 90's in summer. So you need to dress yourself a perfect suit that made only made for cycling. Another thing is that it will often rain in the afternoon for a few minutes. This is why you should cloth properly so that it will be easily adjustable for all these conditions.

Layering is the first principle for bicycle clothing. You should choose a thicker material but add more layers if the condition of weather is cold or wet. This system will help you to adjust in changing temperatures and heat from your body. And you no need to have with a complete set of clothes for every temperature range. In fact it is easy and quick to adjust your clothes by opening a zipper or taking off a layer. Bicycle riding requires much more attention to just your clothing. Anyhow if the weather is too warm or cold, is not suitable for cycling.

Next one is tight fitting dress for your cycling. A baggy jacket not only acts like a braking parachute but also lets cold air get closer to the skin, which makes the wind feel much colder because sweat evaporates directly from your skin. Lastly I would say that bicycle clothing is to keep your skin dry by transporting sweat to the outside. This can help in evaporation without cooling the body too much and without soaking the clothing. Make sure that wet clothes are cold clothes.