Best Bikes at the Best Price - cycleto.co.uk
Types of Bicycle (...in no particular order)
Off-road or mixed - competitive and non-competitive
Although you can ride an off-road bike on a road, they are better in their own habitats as they are designed to deal with the vibration or worse from unsurfaced, loose or very rough ground. Robust frames and wheels are needed, with tyres capable of traction on such surfaces too, so need to have a deeper tread than bikes for the blacktop. You know when you can hear certain bike tyres on the road? That's the sound of all the friction between the knobbly tread and the tarmac, gripping rather too well in this case and requiring harder pedalling than a road bike to move quickly.
Mountain bike is a generic term covering a range of off-road machines. There are the rigid frames, with no suspension built in at all, also the so-called hard tail bikes (because the front forks have suspension), and full suspension versions (with front suspension forks and a rear shock absorber), which are the most capable across rough terrain and include enduro bikes, used for endurance race challenges. You can sometimes lock the suspension for when you are on the road, to prevent loss of energy.
The hard-tails are simpler to maintain, but when riding you'll find the back wheel might skid as there is no suspension there, and you'll be prone to punctures.
Cross-country versions of mountain bikes are designed for speed, and going uphill not just racing down, so are more likely to have larger wheels - 29in giving rise to the term 29er - with wider tyres for crossing very rough ground more easily than the traditional 26in wheel. They'll also have front suspension. In comparison, downhill bikes are not designed to cycle back up that hill at all.
Bike Motor Cross (BMX) bikes usually have 20in wheels and began life as fun racing machines off-road around obstacles. One variant of these are dirt jump bikes, which are for having fun in the air, so these bikes are built to stand up to a lot of punishment.
Fat bikes have fat tyres that roll over all obstacles with ease while cushioning your ride, so are fun and practical too for off-road.