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Suspension: why you need it and how it works

Suspension technology is a key part of mountain biking. What is currently state of the art is actually more likely to be part of a great work in progress than the final form. One happy result of this is that good, reliable designs constantly get cheaper and better. It’s easy to forget how much better suspension forks are now than, say, six or seven years ago, and to realize that for the same amount you paid for the fork back then, you can now get a whole bike with a better fork.

Many people originally resisted suspension forks – the extra weight was a high price to pay for the clunky suspension, which seemed to need an hour of servicing for every hour it was ridden. But even the early forks made bikes feel so much faster, and helped them stick to the ground much better.

Although we now see fewer completely weird designs, radically different approaches continue to evolve, and there is no sign of suspension shaking down into just one clear ’best design’. In fact, sometimes the easiest way to tell what the next favourite design will be is by checking which one is currently being slagged off as outdated.

You would have thought that once we’d decided to fit suspension to bicycles, we could borrow the technology from other disciplines. But it didn’t seem to work out like that. Although many of the best designers working on the problems come from other areas, like John Whyte from Formula One racing cars and Keith Bontrager from motocross, the bicycle seems to need to be thought about in different ways.

One reason is that the power source – the rider – has a low output, and you can’t just slap on a bigger engine. The other is that rider weight makes up a big proportion of the suspended weight, but that weight might vary considerably from one rider to another, even on the same-sized bike.

Suspending disbelief

So, what does it all matter? You can hardly buy a decent mountain bike with rigid forks any more, and full suspension goes up in quality and down in price all the time. All those people who used to say, ’It’s all very well for the kids, but it’s so heavy you can’t climb at all on it’. used to be right. Early suspension was heavy and bounced so much when you climbed that you might as well be trying to hop up on a pogo stick. Some people are still saying this, but we can’t hear them any more because we’ve left them behind at the bottom of the hill.

Full suspension is light enough to climb on now and good design means that full suspension helps you climb by keeping the back wheel pressed down into the ground, finding whatever grip there is to help you up hills. Suspension isn’t just for people who want to jump off roofs – it allows you to blast over rough ground without carefully picking a line as you would with a rigid bike.

Suspension does need more care and attention than other parts of your bike. The first surprising thing is that when it’s new, it needs attention straight away. When you buy a new fork, or a new bike with forks and a rear shock, you need to spend a little time adjusting it. The adjustments are very personal – nobody can set it up for you because adjustments must be done to your weight and reaction speed. It takes maybe upward of half an hour – and you need to take your bike somewhere you can play safely without traffic. Follow the instructions in the sections on setting up your forks and setting up your shocks.

Once your suspension is set up correctly, check and clean it regularly – shocks don’t respond at all to neglect. A check and clean needs no special tools and is easy to do, but it should be done regularly. There’s no harm in checking shocks after every ride, but they also need a thorough inspection once a month – for forks and for rear shocks.

Doing a full service on suspension forks and shocks is more advanced and often requires special tools particular to the make and model of your bike. Previously, the instructions that came with forks were very comprehensive – manufacturers positively encouraged everybody to get in there and get dirty – but in the last few years there has been a clear move away from this. Indeed, most manufacturers now take the opposite stance, with clear injunctions for you to not go further than the basic maintenance and regular inspection set out in the owner’s manual. However, your forks and shocks still have to be serviced frequently, so either go to your bike shop or post the fork or shock off to a shock servicing specialist – see contact details in the back of the book. The strip-down of a fork is to show you the kind of thing that happens when an authorized agent services them.

The same applies to rear shocks – you are expected to keep them clean and lubricated, but not to delve too deeply into their innards, as this will void your warranty.

Remember to increase the frequency of servicing if you ride in sandy, salty or muddy conditions, if you cover a lot of miles, or if you have a reputation for breaking bits of your bicycle.

Part of the mystery of suspension is that talking about it demands all kinds of jargon: terms for the parts, for the adjustments and for how the fork reacts to the terrain. Much confusion arises because most of the words have both a realworld meaning and a suspension-world meaning, which, while not altogether different, is a lot more precise.

“Early suspension was heavy and bounced so much when you climbed that you might as well be trying to hop up on a pogo stick”

Vital elements

Everybody in the industry claims that their design is the best and most unique, but all suspension does the same job. A fork needs only two elements to work: a spring, which allows the wheel to move so you don’t have to, and damping, which controls the speed at which the spring moves.

The spring can be a chamber of air, a coil spring, a rod of springy elastomers or a combination of all three. The spring performs the visible function – shock absorption. When you hit something, the spring gets shorter, absorbing the pressure. The stiffness of the spring controls how far it moves when you hit something – a soft spring gives a lot; a stiff spring gives a little.

The more mysterious element is damping. Damping is vital because it controls the speed of the spring action. Pogo sticks are an example of springs with no damping – if you bounce on them, they keep bouncing. This is great fun on a pogo stick but rubbish on a bike. Damping controls the speed of the spring movement. You may be able to control the speed of the damping with external knobs, or it may be factory-set. More expensive forks allow you to control the speed of the fork compression separately from the speed at which the fork rebounds.

Buttons, bells and whistles

More controls doesn’t always mean better. One of the problems with buttons bells and whistles is that there are as many wrong positions as right ones and, if you’re not systematic, you can make things worse rather than better.

The least familiar function is lockout, which does exactly what it says on the packet. It locks out the suspension, so the bike doesn’t bob around and is particularly useful for smooth climbs and road riding, where you don’t need the suspension. Most useful for climbing are forks that lock out in the compressed position, which helps you to keep your weight over the front wheel on steep bits.

“More controls doesn’t always mean better. One of the problems with buttons bells and whistles is that there are as many wrong positions as right ones”

Learn the language: travel

Travel is one of those suspension jargon words that means exactly what it says: how far your fork travels from its most extended to its most compressed position.

Many early suspension forks were proud of travelling all of 63mm (21⁄2 inches). Today, 100mm (4 inches) is a common fork travel, and travel of 150mm (6 inches) or so is not uncommon.

These longer travels come at a price though – they’re always heavier because you’ve got more fork material, and they have also to be beefier, otherwise they flex too much. Flexible forks are no good because they don’t corner confidently, and they waste your pedalling energy. The other advantage of shorter forks shows up when you climb: long forks lift the front of the bike up, making it difficult to keep the front wheel on the ground during steep ascents.
Similar compromises exist for rear suspension: loads of travel is great for jumping off things, but it is not as handy for climbing up them. Forks with 130mm (5 inches) or 150mm (6 inches) of travel are for freeride and downhill use, as the long springs will absorb big landing forces without too much stress.

Adjustable travel

This is an effort to reconcile the compromises between long travel, which is great for absorbing big bumps, and short travel, which is more efficient for climbing. Certain kinds of suspension forks and shocks are available that allow you to change your travel on the move without getting off the bike, although personally I prefer not to be fiddling around with travel-adjust knobs while whizzing along. Including adjustable travel in a fork adds cost, but it’s worthwhile for
versatility. Be aware that in some forks the adjustability in the travel is obtained by preloading the spring, leading to a higher spring rate for shorter travel settings. This should be an advantage – stiffening the spring in its short-travel, climbing mode – but some people don’t like the way it changes the feel of the bike. Test-ride adjustable travel forks through their range before you commit yourself.

See also bike maintenance tips, tricks and techniques “Troubleshooting wheels”