Bicycling is probably the best way to discover the city of Rio (except maybe for some touristic sites like Pão de Azúcar and Corcovado) and the worst way around in São Paulo.
In Rio, you can get a working bicicletta for a full day delivered/picked up at/from your hotel for 45 reals. Don’t expect a fancy bicycle, and do not worry when they adjust the brake before handing it to you. Rio has 132.5 kilometers of cycle paths running from downtown to the South Zone and Barra de Tijuca. On Sundays, one of the two-way lanes in front of Copacabana and Ipanema beaches are closed to car traffic and that gives ample spaces for cyclists and runners and strollers to enjoy the views. You can go as I did from Capacabana to the Jardim Botânico via Ipanema on decicated bicycle paths with occasional street crossing (I recommend stepping down). Here is the complete route on veloroutes.org. According to veloroutes, it’s 6.4 mi one way, with a maximum of 455.9 ft elevation. Note that you won’t be able to take your bike in the park, but you can leave it within the park at the level of the main entrance.
In Rio, you even have free bicycle road service from SulAmericá S.O.S. Bike service. The mecanos on bike are able to perform free services such as brake tuning, stem tuning, tire inflating, etc. for free!
Bicycling in São Paulo on the other hand is like going through the amazonian forest, alternating between pseudo-bicycle paths “dirt roads” and the actual urban jungle. There is no comparison with the luxury we enjoy in the U.S. Here cars are queens and have priority over people walking by foot or bicycling.
I went to work last Monday by bicycle with a colleague of mine. I never really felt like I was in danger, but it was quite an adventure. I don’t know if I will do it again. Here is the return route we took on our way back, as tracked by my colleague’s GPS.