It is not absolutely necessary to hire a tour guide to visit Sugar Loaf Mountain in Rio. On peak days, however, and especially extremely peak days, a licensed tour guide or a tour operator can make things easier.
A tour guide can buy your tickets at a line-free ticket booth. However, you both still need to wait in line to take the cable cars (gondolas) to Sugar Loaf. On peak days and mainly extreme peak days, those travelling without a tour guide should arrive no later than 9:00 a.m. or 9:30 a.m. to buy your cable car ticket.
Among many advantages of hiring a guide is that a tour guide can answer most of your questions about the sites, the culture, the city, etc, besides he can give you tips for the rest of your stay in Rio de Janeiro. It is worth hiring a private tour guide (with car) if you want to visit several attractions in a short time.
A professional tour guide will speed up the process of visiting several landmarks and monuments in a few hours. On the other hand, if you just want to visit Sugar Loaf and nothing else, than you better do it on your own.
To learn how to visit Sugar Loaf by yourself, get a copy of Sugar Loaf: the definitive guidebook to visiting the Rio de Janeiro’s most famous hill.