Barcelona is a flat city in the city center, so it is a good method to visit to go around on your bike, it is easy to park and gives you flexibility to go from one point to another one faster than walking. Renting a bike is a good way to visit the city and also do some exercise, why not?
Barcelona has good weather all year around, even in winter we have mild weather, rarely we go under 8ºC so with a good jacket in winter and shorts in summer you can take the bike either way.
Where to rent a bike in Barcelona?
There are many places to rent a bike in Barcelona, but in the city center I rented a bike in biketours, I would recommend you to go around the Born area, it is the perfect place in town to go around the week, there are different bike lanes in the main streets.
You can rent a bike to go on your own around the city but they also offer premade tours with guide around the city for 20 euros per person a 3 hour guided tour in different zones of the city.
The prices for bike renting go around 5 euros an hour, and 10 to 15 euros a full day. You normally get a lock in the price to park it in the street. You should get a helmet too for security reasons and if you are not given a map you should get one to see where are the bike lanes in the city.
The city has improved to have more bike lines so you will see plenty on the street while walking and they go all around the city. You can see below a bicing map, Barcelona has a public service to use the bike as a means of transport, but this will not fit into the purpose of visiting the city.
You can see following the pink lines the current bike lanes, the map is updated with the 2014 information, by now there might be some others opened.