No, 26-inch mountain bikes are not obsolete. While 29-inch and 27.5-inch (also known as 650b) mountain bikes have become more popular in recent years, 26-inch mountain bikes are still a viable option for certain types of riders and situations.
26-inch mountain bikes are generally smaller and lighter than their larger counterparts, which can be beneficial for riders who are shorter in stature or who prefer a more agile and maneuverable bike. They are also typically less expensive than larger mountain bikes, which can be a factor for riders on a budget.
In addition, 26-inch mountain bikes may be preferred by riders who do a lot of technical riding or who ride in tight, twisty trails, as the smaller wheels can be more precise and responsive in these conditions.
Overall, the choice between a 26-inch, 27.5-inch, or 29-inch mountain bike will depend on your specific needs and preferences as a rider. It’s important to consider factors such as your height, weight, and riding style, as well as the type of terrain you will be riding on.