Bicycle wheels come in a wide range of sizes from 12" wheels found on smaller Kids Bikes to larger 29" Mountain Bike and 700c Road Bike wheels. Larger wheels are normally faster and more stable at speed and their larger contact patch improves grip too. Smaller wheels are normally lighter, more manoeuvrable and have quicker acceleration.
Wheel sizes are defined by the country that first popularised the style of bike that used them - so you'll see some imperial and some metric measurements listed. Wiggle includes the ISO standard in brackets after each for ease of comparison.
Mountain bikes only evolved about 30 years ago, and inevitably a lot of them never see a real mountain. But their strong frame construction, big tyres and easy going ride position means they're a good option for anyone planning to ride rough terrain. Styles and weights vary enormously, partly depending on price but mainly depending how much suspension you need.
Gentle trails can be easily ridden on a hybrid type bike with thinner tyres, but a proper mountain bike with fat tyres and suspension allows you to ride more challenging terrain with the sort of confidence, comfort and control that will inevitably lead to a lot of fun.
Because so many riders like the robust build and big tyres of mountain bikes for rough roads, an entry level mountain bike is often similar to a hybrid type urban bike. As prices rise, mountain bikes get lighter, faster and easier to ride. Full suspension bikes add extra shock absorption, and increased comfort and control. The new breed of big (29in) smoother rolling wheels and tyres have added another dimension to mountain bike riding in terms of speed, comfort and control.