Mountain bike components - frames
Learn all about the various components of your bike.

Mountain bike components - frames

'When I were a lad' we had 'trackers' with a single gear, cow horn handlebars, made from any bits we could find, and used to ride round the local pit heaps and waste ground.

People took to mountain biking and bikes became trendy
Mountain bikeThe mountain bike is arguably the best thing ever to hit the cycling world. For years a bike was a utility machine to get to work on or get the shopping, or it was an enthusiast's machine with narrow wheels and an equally narrow saddle that really put people off even trying cycling. The image that the racing bike portrayed was one of pain! I once read an article on road racing in a Sunday supplement, it started "The cyclists, slender men who shave their legs" and then went on to describe the masochistic delights of riding a racing bike for 100 miles. It was enough to deter anybody for life.

Then along came the mountain bike with its straight bars, upright position, all the controls at your fingertips, big squidgy tyres, and super-wide range of gears to help you ride anywhere. It was new and it was trendy. People took to this new breed like nothing before and this style of bike rapidly overtook sales of traditional cycles.

The cyclists, slender men who shave their legs" I read. It was enough to put you off for life

The US-style mountain bikes first showed up in the UK in the early eighties. I made my first one in 1983, after having a ride on one that Tony Oliver had made. Everybody laughed and said 'That will never catch on!' (which has to rank alongside Bill Gates's famous '640K is enough for anyone' comment).

All the early mountain bikes were heavy and 'laid back' (shallow seat angle) with huge long chainstays and loads of fork rake - and they tended to 'wallow' a bit. Not much was available in the way of equipment and much cobbling was done to achieve a reliable bike, but it was grand fun! Development of the breed has taken place at breakneck speed and today's sleek, lightweight, disc-braked, suspended machines can trace their lineage directly back to these monsters we rode in the 80's.

The differences between road and mountain bikes have always been great. The most obvious are the fat tyre sections and the flat handlebars. The early frames were made from very heavy tubing, based on the premise that they had to be strong. The first mountain bikes weighed over 30lbs but soon they started shedding weight as the component manufacturers realised this was a growing market that was here to stay. Sun Tour was the first on the market with a full groupset with 'thumb shifters' (non-indexed) and a triple chainset in 1980. Shimano followed in 1984 and soon took over the market, working up to their domination of today.

Bike frames quickly evolved
BikesThe original frames were built from thick wall 'oversize' chrome moly tube i.e. 1 1/8" diameter top tube and 11/4" down tube. Very quickly the frame design evolved:
  • Shorter overall (wheelbase - distance between hubs)
  • More distance between the saddle and bars (longer top tube, longer handlebar stems)
  • Much shorter rear end (chainstay)
  • Steeper seat and head angles
  • Much less fork rake.  
The first mass produced mountain bike was the Specialised Stump Jumper in 1980, made possible by the Sun Tour groupset, and soon many other manufacturers followed the trend. In the 80s and early 90s experimentation was where it was at: every person and their dog came out with ideas that would 'revolutionise' mountain biking. Some were just plain silly, others, like aluminium frames, suspension, SPD clipless pedals and indexed gearing became part of the mountain bike we know today.

So what has happened to the mountain bike in the 20 or so years it has been around?

The first mountain bikes had horizontal top tubes the same as road bikes, though this put a restriction on stand over height and front end height. The frames were built with lugs, which constrained them to this design. (It is handy to have extra clearance between the rider and the frame in case of a sudden halt!). To gain more stand over clearance the frames were made smaller, but this lowered the bars too much.

The answer was found by sloping the top tube down from the head tube to a shorter seat tube. By TIG welding the frame it could be made without using lugs. The chainstay length became much shorter and the head and seat angles got steeper giving a much sharper handling bike. Tyres went from wide to narrow, to wider again, with hundreds of tread patterns, each claiming to be the best. The original handlebars were the 'bull moose' pattern - a Y-shaped extension welded onto the bars so they were fixed in position. This gave way to separate bars and stem, giving some adjustment on the angle, thus aiding wrist comfort and a choice of handlebars. Very wide bars were tried, and so were very narrow bars! Today we seem to have settled on a comfortable compromise.

By about 1991-92 the frame design had settled down to 71° head angle, 73° seat angle, with a longish top tube i.e. an 18" frame would have a top tube of between 223/4" and 23". Since then, the trend has been for top tubes to be marginally shorter but the rest of the frame design has stayed remarkably similar.

In 1990 an ex-motor-cross mechanic, Paul Turner, introduced the first commercially viable suspension fork. Rock Shox are still the leaders in bicycle suspension technology.

In 1990 an ex-motor-cross mechanic, Paul Turner, introduced the first commercially viable suspension fork. His company, Rock Shox, are still the leaders in bicycle suspension technology. Once the system was accepted (aided by a win in the World Championships by Ned Overend), a host of different designs appeared using variously: air, steel springs, plastic elastomers, rubber blocks and even a carbon fibre ring as springing mediums, and oil or friction as the damping medium. (A spring simply stores energy, which needs to be controlled, otherwise the rider will simply get bounced all over!)

Today, all suspension forks are of a similar telescopic design. The better ones use air as the springing medium because by altering the air pressure it is infinitely variable. Likewise, oil as the damping medium is very controllable by valves. The budget end of the market tend to be steel spring with oil damping, or plastic elastomers which can be made to be self damping to a certain extent. Both of these systems however are less controllable than oil - air. Very few mountain bikes are seen without suspension forks nowadays, even the £150 specials sold by many large, out-of-town-bicycle-retailers sport them.

Once riders discovered that they could go faster with front suspension, because it absorbed the impacts and kept the tyre in contact with the trail surface, attention inevitably turned to suspension for the rear wheel (in the frame). After all, it has been successfully used on motorbikes for many years. Many alternative systems were marketed by different manufacturers, each claiming their design to be 'the ultimate'.

The main problem with rear suspension is keeping the chain length constant under load. The 'unified rear triangle' seems to be the best design for this, where the complete rear triangle including the bottom bracket is pivoted just above and in front of the bottom bracket shell via a spring/damper unit, usually mounted on a Y-shaped frame. Other methods use a system of links designed to lock out when the rider stands on the pedals.

All suspension systems need a lot of maintenance. They are full of moving parts that inevitably wear with use

Full suspension bikes (front and rear wheel) were first embraced by downhill riders who did not worry about the weight penalty, but full-suspension frames are now commonly used by cross-country racers as designs and technology have allowed the frames to be made lighter and more reliable. All suspension systems need a lot of maintenance. They are full of moving parts that inevitably wear with use, so you must be prepared to spend both time and money to keep them in good condition.

Mountain bike brakes have developed dramatically from the original cantilever brakes with motorbike levers. Cantilevers were the ideal first choice when mountain bikes were first born. They were effective, could be fitted to suit any tyre size and collected a minimum amount of mud. But they weren't ideal. In the mid 1990s Shimano produced the V-brake. This was much more powerful. Its vertical arms brought the brake block directly onto the rim - unlike the arc of the cantilever - and its slimmer profile meant it didn't catch on the riders' heels or knees. The V-brake has all but taken over the mountain-bike market except on the most expensive bikes which now use disc-brakes.

As down hill racing (DH) has developed into a sport of its own, so the technology applied there has had to keep pace. Borrowing heavily from the motorcycling world, light weight is not an issue: speed and control are. DH frames are long, with up to eight inches of suspension travel both on the front fork and the frame itself, to allow the rider to pick the fastest line without being thrown all over the place. Speeds reached by these riders can be alarming, and these behemoths need powerful brakes.

Hardly surprising then that disc-brakes are now the norm on all DH bikes. Inevitably, disc-brakes have migrated onto cross-country bikes too. The advantages of a disc are: very powerful braking, unaffected by wet or buckled rims, and it does not contribute to any mud build-up at the fork crown, seat stays or chainstays.

Most mountain bikes sold never go off-road in any serious fashion, but they have made cycling popular thanks to their user-friendly design and comfort

Despite their name, most mountain bikes sold never go off-road in any serious fashion, but nevertheless they have introduced or re-introduced many people to cycling thanks to their user-friendly design features and comfort. Even if only a small fraction get serious about the sport, or just make one journey a week by bike instead of by car, this has to be good.

In the space of just a few years the mountain bike has moved from being the plaything of a few Californian friends to become an international fashion accessory, a status symbol (some riders will spend more on their bikes than their neighbours would spend on a motorcar), a serious sporting machine (Mountain biking is in the Olympic Games) and highly practical machine for utility or touring purposes. It's a breath of fresh air. If you haven't ridden a mountain-bike yet, you don't know what you're missing!


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