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Anatomy of a mountain bike

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Knowledge level: Beginner

Mountain Bike

Article posted: 02/04/2014

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Within the blanket title of mountain biking, there are broad spectrum of disciplines, such as cross-country, downhill and free-ride. Despite the increasing specialisation of bikes for each of these disciplines, a cross-country orientated hardtail is a sensible and versatile choice for the majority of riders.

Wheel sizes also vary and although 26” was the standard, 29” and 650b (27.5’) are becoming increasingly popular and commonplace. For general trail riding though, you’re most likely to come across and be riding a cross county orientated hardtail.

Suspension fork

Suspension forks smooth out the trail, absorb impact and enhance traction. Different forks will offer varying degrees of travel, the amount of vertical movement the fork allows. For trail bikes the current trend is for longer travel forks offering 140-160 mm but more race orientated 29” bikes especially will often have as little as 80-100 mm. More travel will generally mean a more forgiving ride and a slacker head angle, which makes them suited to steep and technical descents. However long travel bikes can be unwieldy, heavy and inefficient to climb on. The amount of travel will be dependent on the sort of riding you intend to do.

Forks use a combination of springs and air to deliver the suspension and, depending on the make and model, allow you to tune how stiff the fork is and how it behaves. Most forks allow you to lock out the suspension, which can be beneficial on non-technical climbs, and some have a remote handlebar lever to do this. Until fairly recently the bikes wheels would lock into the fork’s dropouts with a standard 9 mm quick release skewer but, for the improved stiffness they offer, 15 mm and 20 mm thru-axles are becoming standard.

Brakes

Hydraulic disc brakes are now standard on almost all mountain bikes, although cable operate ones may be specced on cheaper and entry level bikes. Hydraulic disc brakes have revolutionised mountain biking and, by keeping the braking surface away from the trail and offering reliable control, power and modulation not matter how foul the conditions, have allowed riders to push the limits of the sport. Basic maintenance simply involves changing the pads when they become worn but occasionally the system may require bleeding and, although manageable at home, does require a specialist bleeding kit.

Gearing

Mountain bikes have a wider range of gears than road bikes, to enable you to tackle steep, slippery and technical terrain. A wide ranging rear cassette will typically offer sprockets ranging from 11t to 36t. The front chainset will usually be a triple with a 44-48t outer, 32-36t middle and 22-26t inner or “granny” ring.

On more race orientated bikes, especially 29-ers, double chainrings, typically 39t/27t are becoming standard. Another recent shift is towards single chainring set-ups and super wide, 11-42t, cassettes. For their simplicity, reliability and ease of maintenance, you can expect to see single ring set-ups become increasingly commonplace.

Wheels

Mountain bike wheels have to be strong, light, stiff and have wide enough rims to accommodate high volume tyres. Although top cross country racers will use carbon rims and sometimes tubular tyres, alloy rims with clinchers are by far the most common. The disc brake rotor attaches to the hub either with six bolts or using Shimano’s Centre Lock system that uses a lock ring.

Rotor sizes vary from 160 mm-203 mm with smaller rotors used for cross country where weight is crucial and the larger sizes, which deliver more powerful stopping, in downhill disciplines. As we have already mentioned there are currently three wheel sizes commonly found on mountain bikes and which to choose is a matter of heated debate. The original 26” size is becoming less common on new bikes but parts are still easily available. Cross country and taller riders seem to be leaning towards 29” wheels and a middle 650b (27.5”) size seems to offer a best of both worlds solution for general trail riding. There are definite pros and cons to each wheels size and you will probably get a different opinion from every rider you speak to. The best way to decide is to test ride a few bikes with different sized wheels and see which feels best to you. Find a local bike shop that you trust, discuss the type of riding that you intend to do and they should be able to advise you on suitable options.

Tyres

The choice of widths, tread pattern and rubber compounds of mountain bike tyres can be truly bewildering. It’s worth talking to some experienced local mountain bikers or consulting with your bike shop to determine the best tyres for the type of riding and trails you’ll mostly be tackling. A significant decision you’ll need to make is whether to run a tubeless setup or stick with inner tubes. If your rims are tubeless ready and you buy suitable tyres, setting up should be simple and tubeless is definitely the way to go. You can convert non-tubeless rims and tyres but it can be bothersome and messy. The most significant factor to how much grip you get off-road is tyre pressure so a decent pump with an accurate gauge is essential. 

Frame geometry and material

Cross country racing bikes will tend to have a fairly aggressive “head down and backside up” geometry with fairly steep headtube and seat-tube angles. As longer fork travel and downhill ability become more of a priority than speed on the flat and climbing prowess, angles will become slacker. Again, more experienced riders and your local bike shop should be able to point you in the right direction depending on the type of riding you intend to do.

Mountain bike frames come in a number of materials including alloy, steel, carbon and titanium. Every bike frame material has its pros and cons but, no matter what material you choose, quality is key.

Pedals

Many novices and plenty of more experienced riders are more comfortable riding off-road with flat pedals. If the terrain gets too much, they make it easier to put your foot down or even walk the sections. Mountain biking flats have aggressive pins on them which bite into the soft rubber soled shoes you will wear. 

Clipless pedals offer advantages too, such as improved stability and peddling efficiency. Mountain biking clipless pedals are multisided for easier reengagement and usually have a mechanism to clear mud. The cleats are recessed into the souls of the shoes to make walking easier. Which you choose mainly comes down to personal preference.

Saddle

Mountain bike saddles don’t differ too much from their road cousins. They sometimes have beefier rails, a narrower rear to allow you to slide off the back of the saddle and a more robust covering. If you have got a make and model of saddle that works for you on the road though, there is no reason not to put the same on your mountain bike. Some mountain bikers do opt to fit a dropper seat post which, using a bar mounted lever, allows them to drop and raise their saddle in response to the demands of the trail.

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