The most common gearing options in the mountain bike world are 1 or 2 chain rings paired with a wide-range 10-speed cassette. The chain is shifted from cog to cog using a front derailleur over the crank and a rear derailleur by the cassette. Value-minded bikes will have fewer cogs (or speeds) on the cassette. A drivetrain with 2 chain rings and 10 cogs on the cassette will have 20 speeds (2 x 10). Additional speeds on a cassette create smaller gaps between shifts: say you're pedaling up a hill and your legs are starting to burn, a downshift on a 10 speed cassette will be less noticeable than a downshift on a 7 speed cassette. The newest trend for drivetrains is a single chain ring paired with an extremely wide-range cassette. This saves weight, reduces complexity, and gives you almost the same range.

Weight, hub engagement, and rim width all have a massive impact on how  well a bike performs. With advances in carbon fiber, aluminum  extrusions, and the rise of disc brakes, rims are getting lighter,  stronger, and wider. A lighter rim decreases the rotational mass of a  wheel, making it easier to accelerate and change direction. Another  factor to consider is rim width. Wider rims give tires more support  while cornering, and change the shape of the tire to improve traction.  The last thing to consider when looking at wheels is rear hub  engagement. Engagement is how many degrees the cassette can turn before  it drives the wheel forward. In technical terrain, a smaller degree of  engagement allows you to keep your pedals where you need for quick power.

Modern mountain bikes use disc brakes to deliver excellent stopping  power and control in a wide variety of conditions. A brake lever actuates a caliper; pistons in the caliper compress the brake pads on to the rotor which, in turn, slows the wheel. There are two types of disc  brakes: mechanical and hydraulic. Mechanical brakes use a cable to actuate the caliper. These brakes are are easy to service, and work  great in cold temperatures. Hydraulic brakes use hydraulic fluid to  actuate the pistons, just like you would find in a car or motorcycle.  They have more stopping power and better lever feel, or modulation, than mechanical brakes. They do require a bit more maintenance and periodically must be "bled" of air, for optimum braking performance. 

Carbon and aluminum are the two most common materials for mountain bike frames, each with distinct advantages. Carbon frames are lighter and absorb vibrations better, offering a smoother ride on rough trails. Aluminum frames are more affordable and durable, ideal for budget-conscious or rugged riders. Carbon's superior strength-to-weight ratio makes it a favorite for high-performance bikes, while aluminum's stiffness provides reliability and easier repairs. Carbon frames allow for optimized designs, balancing stiffness and compliance, whereas aluminum offers ruggedness and resilience. Both materials cater to different riding styles, making the choice dependent on your performance goals and budget.

Wheel size will be one of the most important variables to look at when shopping for a new mountain bike. Currently, the most common sizes are 27.5 (650b) and 29-inch wheels. In the past, mountain bikes all ran on 26-inch wheels. Standards have since given way to several wheel options. After the widespread adoption of 29-inch wheels in the late 2000's, manufacturers started to look at wheel size to make performance gains. 27.5 emerged as a great compromise that balances most of the maneuverability of their 26-inch cousins, but delivers much of the efficiency and technical ability of the 29-inch wheel size.

Mountain bikes come in three types: rigid (no suspension), hardtail (front suspension only), and full suspension (suspension at both ends). Suspension enhances comfort, control, and handling but adds weight to the bike. Basic suspension systems use coil springs with limited adjustability, while advanced systems use air springs and offer fine-tuned adjustments for better performance. Suspension travel, measured in millimeters, shows how much the system compresses to absorb impact, with more travel suited for rough terrain. For example, 100mm of travel (about 4 inches) is ideal for smoother trails, while longer travel handles more challenging conditions. Higher-end suspension systems generally deliver better performance and adaptability for varying trail demands.