[Life_N_Cancun]

I am thinking about buying a bicycle (NOT a motorcycle...yet) and have a few questions. I am in Cancun, the majority of bicycles I have seen have been cart types and they just share the road with cars. What is the law or accepted behavior with reguards to riding on the roads vs. sidewalks? Is there a halmet law of any kind that is enforced in Mexico? Finnally, can I chain my bike up to whatever I can find, (street sign pole for example) of do I have to leave it unchained (never happen) if there is no bike rack around? Any experiences relating to this topic would be helpful. Thanks