There is a reason why film crews and pro athletes choose Mexico as a destination for mountain bike films. The scenery is spectacular along the coast, and the trails in the mountains are flowy and grippy. Whatever kind of riding you are looking for, Mexico has something to get you stoked. People rave about their experience riding in Mexico. The best part is that any time of year (with the exception of rainy season in some areas) you can find riding.
The weather is the other obvious perk. In the fall and spring are great options along the coast, with warmer weather where you can combine some time on the beach with some time on the bike. The dry season runs from December to April, when there is virtually no rain. December to February are the cooler months, so pack a layer or two, but are optimal for riding more inland. The temperature can still be as high as 80 degrees in the dry season, so it's not exactly "cold weather riding." The wet season lasts from May until October, but you are usually safe going in the early and late part of the wet season.
The culture and food is a big reason to head to Mexico for your next bike trip. Each region in Mexico has its own unique cuisine, but if you're a lover of tortillas, hot sauce, fresh fruit and vegetables, and tequila, you'll be incredibly happy. In Oaxaca, you can sample Mezcal directly from the distillery, and even tour agave fields and see how it's prepared. Along the coast, you can expect fresh seafood dishes. During the time when you aren't mountain biking, you can explore nearby towns and cities, visit open air markets, and even time your trip to attend festivals or events.