Like every sport, mountain biking has evolved and thus developed its own lingo that may be confusing if you are a newer rider.
When it comes to the different types of bicycles you can ride, nothing can beat the simplicity and stability of a hardtail mountain bike.
A hardtail mountain bike simply means a bicycle that has no rear suspension. The rear triangle that connects to the seat post on one side, and the wheel axle on the other side is void of any suspension components.
This rear triangle has an upper set of tubes and a lower set of tubes. The upper tubes on a hardtail mountain bike are referred to as the upper stays, while the lower tubes on a hardtail mountain bike are referred to a the lowers stays, or chain stays.
Remember, just because the rear triangle on a hardtail mountain bike appears solid doesn’t mean there is not any flex. Flex can be designed into a well developed hardtail mountain bike in order to improve its handling capabilities. On the flip side, a poorly built hardtail mountain bike might have excessive flex in the rear, often referred to as the noodle effect and could break or even cause excessive crashing.
With the advent of XC carbon mountain bicycles, bicycle engineers and designers can control specific amounts of flex to more of the areas they choose with much greater accuracy over conventional metals like aluminum or steel.