Mountain bikes are to cycling what the four-wheel drive is to driving: + rugged-looking beasts that rarely get off the streets of suburbia and on to the+ hills for which they were designed. Yet the great outdoors is where they are + most at home. Most children (and adults) have at some stage taken their + standard bikes off-road, and discovered that bits fall off them and snap, tyres+ get punctures, gears never change properly, and when they do work there aren't+ enough of them.With a modern mountain bike such calamities are history. The + frames and components are designed to take everything that you can throw at + them - within reason; the heavy-duty tyres take rocks and thorns in their + stride; and there are up to 24 gears, all of which can be smoothly engaged. + Once on trails, or bridleways, it is easy to see why this is the + fastest-growing sport in Britain. The saddle of a bike is a far better vantage + point from which to explore the countryside than a car, and you see much more + than you would walking. On top of this, it's great exercise: a day of off-road + cycling will have everyone sound asleep at night as soon as their heads hit the+ pillow. But perhaps the best bit of all is that after every lung-bursting + climb comes the thrill of bouncing downhill. In spite of this, there are still + relatively few mountain bikes in their "natural" environment. Huw Williams, + deputy editor of Mountain Biker International magazine, feels that part of the + problem is access. "There are a limited number of places where people can ride+ legally in this country," he says, "especially once they're in popular + recreational areas such as the national parks, and I think this plays a part in+ discouraging people." (See box.)Which is rather a shame when you consider how + much fun real off-roading can be. I used to lead guided mountain bike rides + around the coast of South West Wales which would attract all ages (the youngest+ were nine and 10, the oldest in their sixties), and while some were initially + apprehensive, by the end of the day most of them were born-again + bike-riders.Admittedly south-west Wales is not renowned for its mountains, but+ even small hills can be challenging, and it is here that the inexperienced + need particular help. Children, for example, will attack a hill until they get + the better of it, or vice versa. It is only older children, usually boys, who + have reservations about getting off and pushing. If you are accompanyi ng a + group, or even your family, the best way to deal with hilly rides is to go at + the pace of the slowest rider and, if they get off and push, do the same + yourself. In this way, fitness need not be a problem, and if you start to ride + regularly you'll soon find yourself riding up hills that would once have meant + a long slog on foot.Access is one of the most contentious issues surrounding + the sport, with everyone from ramblers and horse riders to farmers and + environmentalists wailing about the impact of mountain bikes on the + countryside. However, if you are riding on a legally accessible trail, you have+ just as much right to be there as they do. The main thing, as with all outdoor+ sports, is to show consideration for others: don't tear up behind walkers and + riders; warn them of your approach and ride past slowly. As for erosion, try + not to skid unnecessarily on wet grass and soil, although independent research + has shown that mountain bikes cause no more erosion than walkers' boots and a + good deal less than horses' hooves.If you pass through gates, always close or + fasten them behind you. Don't disturb livestock, and make sure you always know + where you're going, so you don't end up riding through a field of crops after + making a wrong turn.Mark your route on a map before you set out (and know how + to read it!) so it's easy to follow on the trail.Everyone falls off at some + point - a rock, pot-hole or tree root will catch you out eventually - so the + golden rule is to wear a helmet. Always. It's also useful to carry a basic + first-aid kit, and, as Huw Williams advises, "don't stray too far out into the + wilds, just in case you do have an accident". Many of the more experienced + riders who go up into the mountains of Scotland and the Lake District even take+ mobile phones in case they come to grief in a remote area. Teachers might + agree that this would be a good occasion to have one.