Hi there! JUst going to throw some information out for people who are new to the sport. *A lot of this information comes from REI"s article but this is all general knowledge. *

Types of Mountain Bike Terrain 

 
Singletrack, the most common trail type, has a width that varies from just a little wider than your shoulders on up to a track that"s just wide enough for two bikes to pass.

Doubletrack trails are normally double the width (or more) of a typical singletrack trail with enough room for two bikes to ride side-by-side. Often doubletrack trails follow abandoned logging roads, fire roads or power-line roads, where the tires of vehicles created two single tracks.

Mountain bike terrain parks are popping up everywhere from jump-and-pump tracks under urban overpasses to lift-serviced trails at ski resorts. Expect such features as elevated bridges, halfpipes, jumps of various sizes, berms, banked corners and hairy downhill switchbacks.
 

Mountain Biking Styles

 
*Trail: *Arguably the most common mountain biking style. Used for riding a mixture of climbs and descents with no specific type of racing in mind. Bikes in this category place equal emphasis on fun, efficiency and sensible overall weight. Typical specs: 120–140mm of suspension travel; 67–69° head-tube angle

All-mountain/enduro: Think of all-mountain riding as trail riding on steroids, with bigger leg-burning climbs, longer, scarier descents and more technical features—both man-made and natural. Bikes for all-mountain riding are designed to perform well on steep descents while also being light and nimble enough to pedal uphill. Typical specs: 140–170mm of suspension travel; 65–68° head-tube angle

The term enduro comes from the racing world and describes a competition that has timed downhill stages and untimed uphill stages. The winner is whoever has the fastest combined time on the downhills. Enduro riding has become very popular, and the term is now often used interchangeably with all-mountain regardless of whether you’re racing or not.

Downhill/park: Mostly ridden at lift-serviced bike parks. Downhill bikes are big and tough, and riders wear full-face helmets and body armor as they encounter jumps, berms, rock gardens and wooden ladders. Typical specs: 170–200+mm of suspension travel; 63–65° head-tube angle

Cross-country: This style of riding typically implies riding fast, with an emphasis on climbing prowess. Distances vary from just a few miles to 25-plus, and bikes tend to focus on efficiency and low weight. These bikes can be great if you’re considering getting competitive or would like a racier ride for your local trails. Typical specs: 80–100mm of suspension travel; 70–71° head-tube angle

*Fat-tire biking: *Oversize tires, from 3.7 in. to 5+ in. wide, give these bikes excellent traction, especially in sand or snow. Fat-tire bikes are great for beginners because the wide tires are reassuringly forgiving as a rider picks a line through rough terrain.
 

Types of Mountain Bikes

 
Rigid: While not the most common type of mountain bike, “rigid” mountain bikes don’t feature any suspension. They are easy to maintain and usually less expensive, but most riders prefer bikes with suspension for greater comfort. Most fat-tire bikes are rigid, and riders find that the wide tires and low tire pressure provide all the squish needed to absorb bumps in the trail.

Hardtail: These bikes have a suspension fork in the front to help absorb impact on the front wheel, but the rear of the bike has no suspension—ergo a hardtail. Hardtails are typically less expensive than full-suspension bikes, and have fewer moving parts (which often translates into less maintenance). Most hardtails have the ability to lock out the front fork for times where a fully rigid bike is desired.

Cross-country riders typically gravitate toward hardtails as they allow more direct transfer of power between the pedal stroke and the rear tire. Hardtails can also be at home on all-mountain trails, and the lower cost and easier maintenance make them a solid option for everything except serious lift-serviced downhill trails.

Full suspension: There are many variations of full-suspension bikes, but the general idea is for the front fork and rear shock to absorb the impacts of the trail. This drastically reduces the impact on the rider, increases traction, and makes for a more forgiving and enjoyable ride.

A full-suspension bike can soak up a lot of a trail bumps and chatter, but the bike can also “bob” a bit and you lose some of the energy transfer when climbing uphill. As a result, most full-suspension rigs have the ability to lock-out the rear suspension to offer better power transfer and more efficient climbing.

Bikes designed for downhill riding typically boast a lot of travel—the amount of movement in the suspension—compared to bikes designed for cross-country and all-mountain riding. As much as eight inches of travel front and rear is fairly common.
 

Wheel Size

 
26 in.: All mountain bikes use to be equipped with 26 in. wheels. It is still a popular wheel size for its responsiveness and maneuverability.

*27.5 in. (650b): *Offering a middle ground between standard 26 in. wheels and 29ers, these bikes apply a “best of both worlds” solution, more easily rolling over terrain than the 26s, but more maneuverable than 29ers.

29ers: The bikes featuring 29 in. wheels that are typically heavier and a little slower to accelerate, but once you start moving you can conquer considerably more terrain easier than on a bike with standard 26 in. wheels. They generally offer excellent grip and they have a higher “attack angle”—meaning the wheel rolls over trail obstacles easier.

24 in.: Kids’ mountain bikes typically have 24 in. wheels to accommodate the shorter legs of children. Most are less-expensive versions of adult bikes with simpler components. Generally speaking, these suit kids ages 10 to 13, but this depends more on the size of the child than the age. Younger/smaller children can get started biking with 20 in. wheels.