In Huaraz , there is at least one agency that has well-maintained mountain bikes, Trek or better, with front suspension. The other agencies, mostly along Luzuriaga, have cheaper bikes and often do not supply helmets.
The best day trips and views are to be had in the Cordillera Negra , which has single-tracks that lead a thousand meters back to Huaraz. Longer trips can take you up and over the Cordillera Negra  to the Pacific Ocean or through the Cordillera Blanca , on valley single-track, and over 4,500-meter passes. The longer trips require support vehicles to carry gear.
Julio Olaza at Mountain Bike Adventures (Lúcar y Torre 530, tel. 043/42-4259, www.chakinaniperu.com ) offers a range of guided mountain bike trips and bike repairs. Julio is a longtime Huaraz  resident who speaks perfect English. Rental rates, which include a guide, start at US$35 per day.