A buyer's guide to mountain bike suspension. - Dirt

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Suspension

A buyer’s guide to mountain bike suspension.

How to choose your forks and rear shocks

We run through all the basics you need to know when choosing suspension, whether as an after market upgrade or on a new trail, enduro or downhill bike.

On most serious mountain bikes you’ll find suspension front and rear unless it’s a hardtail. A well designed bike will have geometry and sizing built around the suspension travel and will be all the better for it – we’re at a point with mountain bikes where not only has technology improved but so has the design team’s experience in picking the right blend parts and thinking for the job in hand.

If you’re new to mountainbiking you’ll be best served by buying a bike as a whole and here at Dirt we’ve got guides to buying trail, enduro and downhill bikes – covering all the basics on what amount of suspension travel you need for each type of riding and what type of fork and shock is most suitable. Check these guides out if you need a starting point.

If you’re an experienced rider and you’re looking to upgrade your forks or shock to either replace worn or ageing units or gain a performance advantage then you’ll need to look carefully at what suits both your bike and your riding style.

It’s not simply a case of bolting what you fancy owning onto your frame – it needs the correct dimensions and fittings.

Here’s our break down of the basics you need to know for mountain bike suspension.

FORKS

Suspension forks are usually telescopic – two upper legs sliding within a one piece lower leg assembly – and will be either single crown or dual crown. There are other options out there, notably the Cannondale Lefty, but they’re a rare sight. The forks not only need to give you control and comfort from the suspension action but need to track and steer well, keeping you on line. The damping needs to work with the spring action, supporting the bike through rough terrain and giving a consistent feel especially on long descents.

There’s been huge improvements over the last few years to all aspects of the forks. The structure and chassis build has become more purposeful, giving better steering and braking control. Damping has advanced and become consistent, reliable and suitable for the job in hand. Tapered steerers and bolt through axles have helped too, giving even lighter weight trail forks the stiffness and control that a serious gravity fork would have had only a few years ago.

The length of the fork (axle to crown) and the travel (the amount of movement the fork gives) also play a big part in the suitability.

Springs and dampers.

Air will be the spring on most trail and enduro forks – with a positive and negative air chamber usually controlled by a single valve. This sits in one leg with the oil damping system in the other. Set the air spring to suit you weight and then adjust the damping to control the action of the fork. Coil springs in trail and enduro forks have almost disappeared now and even DH forks which have a history of reliable coil sprung units have started to make the change. The progressiveness of an air fork’s spring curve can be easily adjusted via volume spacers, allowing riders to fine-tune the feel as well as the spring rate via a change in air pressure.

 

Axles and fit.

Front wheel axle spacings have been a standard 100mm (between the fork legs) on most trail and enduro bikes for some time. Now we have the Boost spacing option of 110mm for 29ers and 27.5 ‘Plus’ sizing. These become an option on many trail/enduro forks so check this detail before buying. The ‘open’ dropout option for traditional quick release skewers has almost faded away and on a seroius bike you’ll have a bolt through hub with a 15mm or 20mm axle standard.

The length of the fork (axle to crown) and the travel (the amount of suspension movement the fork gives) also play a big part in the suitability. A longer fork with more travel may be a tempting upgrade but it will slacken the head angle and raise the bottom bracket height – a compromise or an upgrade? Tread carefully as a well designed bike will be designed with a certain travel fork in mind. Adding 10-20mm of front fork travel may be OK but it’s likely that any more will disturb the bike’s handling.

Structure.

Forks in all categories have seen increases in performance through not only suspension action and control but through a more purposeful construction. The lower legs are one piece with an integrated brace stiffening up the structure and keeping the weight low. The upper legs have dropped in weight too, and have a bonded or one-piece crown and steerer, and this, along with a bolt through axle gives very accurate steering, less flex, more grip and better braking control.

Here we take a look at the differences between trail, enduro and downhill forks.

 

The RockShox Pike showing sag indicators and air pressure settings chart.

TRAIL FORKS

Short to mid travel trail bikes have gained ability in recent years through better geometry, a more purposeful frame build, bolt through axles, tapered steerers and stiffer wheels – take a look at the latest 2017 Trek Fuel EX for an example of this.

Trail forks to suit these frames will usually have a similar travel to the rear suspension (occasionally 10mm more) and this will be from 120mm to 150mm. The upper leg diameter will need to be larger on forks with more travel to stiffen up the chassis, reduce flex and increase steering authority with 34mm or 35mm being a suitable size. This is an area where trail forks have improved enormously over time.

An air spring is the way forward with a quality trail fork, with a positive and negative air chamber being charged by one valve. Pressures will be lower than on a rear shock in most cases and with RockShox they have a guide sticker on one leg as useful starting point for base settings. Fox have a download available with sag and pressure settings for all their forks.

The damping is in the opposite leg to the air spring and this will usually have a rebound adjuster (for the return speed of the fork) and a compression adjuster with maybe a full lockout feature, handy for long fire road climbs or road transfer sections. Familiarising yourself with how these features affect the forks characteristics are essential to getting the the performance and set up correct. A more refined fork will have a better damping system, giving you more support within the travel and consistency when crashing through relentless and testing terrain – this is what you are paying for as you progress through the price range.

For trail riding, a stout fork that offers good tuning ability will weigh in around 2Kg and should be available in both the 27.5″ or 29″ wheel size. The RockShox Pike, Revelation and Yari or Fox 34 are recommendations from us here at Dirt. With the new Rhythm 34 fork from Fox due on 2017 production bikes it’s good to see more affordable options too.

The Fox 36 with 15mm or 20mm bolt through axle system.

ENDURO FORKS

We’re into 160mm and 170mm travel here when it comes to forks for an enduro bike. A more serious chassis and build to mate up with a frame with comparable travel. A fork for pushing into more challenging terrain, where damping control and support is as important as just how much travel is on tap. Of course with more travel on a longer length fork you need stouter upper legs to control the twist and flex that they will be subjected to along with the ability to handle stress from high speed braking.

Air springs are now standard with coil rarely seen – again this keeps weight low and tuning easy. Volume spacers can be added to the air chamber to adjust the spring curve giving you a more progressive action to the fork – this is a recent development and a really easy way to experiment with the feel of the fork.

Damping will be more advanced here, with technology borrowed from the downhill world more so than the trail/XC category and the forks are all the better for it. After all, you could be racing a mini DH event or hitting bike parks such as the Black Mountains Cycle centre on these forks and they need to take the big hits and landings in their stride as well as deal with the intensity of long rough tracks. Low speed and high speed compression damping will often be standard features, along with the usual rebound adjustment. Most enduro forks will start at a higher price than a trail fork and can be a more specialist piece of kit – it can take some experience to get them dialled in, so seek advice if needed.

Take a look at our long term test Orange Alpine 160 – a great example of a well sorted enduro bike – and you’ll see we have run this with a variety of 160/170mm forks. The Fox 36, Bos DeVille, Manitou Mattoc and RockShox Lyrik are all suitable class leading forks in this category, with 35/36mm diameter upper legs, tapered steerers and advanced damping. On a long travel 29er the Ohlins RFX is a sound choice with more options for this brand for 2017.

The dual crowns and direct mount stem fittings on a RockShox BoXXer.

DOWNHILL FORKS

A downhill bike needs a very specific fork – and here we see a dual crown fork with a four bolt direct mount stem as standard kit. Look at some of our favourite DH bikes, the Specialized Demo, Canyon Sender and Solid Strike and you will see purpose built forks that work in harmony with the rear shock and frame geometry.

Travel of around 200mm is common, with air springs very much now the thing, in territory where coil springs once ruled. We’re talking a more substantial build again, with upper legs of 35-40mm and a wider 20mm diameter hub with a 110mm spacing – you’ll need a DH specific wheel to fit these forks and a frame designed to take a fork of this nature. Four pot brake calipers slow a downhill bike from serious speeds and here you’ll find disc rotors of 200mm+ in diameter and these forks have legs and the stronger, stiffer structure to deal with the increased barking forces.

Air springs keep the weight of an up-to-date DH fork as low as possible, with a top end fork hitting the scales at 2.6kg – a good reason we’re seeing downhill bikes weighing in around the mid 30 pounds mark. The low to mid price DH forks will usually be coil (the RockShox BoXXer Team and X-Fusion RV1 being good examples) and this is no bad thing – they’re proven, reliable and easy to work on. However, Marzocchi who are famed for their smooth and very reliable forks, choose coil springs even for their premium level 380 C2R2 Titanium model forks.

So, with the additional support and stability of a dual crown, a stronger more capable chassis, a 20mm bolt through axle and an air spring, DH forks are a truly evolved product. Downhill bikes are lighter, more balanced and faster than ever and the dual crown fork is all part of the package, allowing you to push the bike harder with more confidence. 27.5″ wheels are now common place but with plenty of 26″ bikes out there we’re not short of options in this size too.

Check out the 2016 Dirt 100 for our pick of the current DH forks on the market.

Ohlins have a huge pedigree in suspension and have now moved into the mountainbike world.

REAR SHOCKS

Forks are an area where many riders focus their spend or sights on when it comes to building or choosing a mountain bike where as the rear shock often gets overlooked a touch. Like the forks though, they’re all part of a system, working at one with the frame and fit for the job in hand.

As with front suspension forks as you spend more on a rear shock you will want to see not only performance benefits but find a shock that is right for your bike’s set up, balancing the ride qualities and characteristics front and rear. More specific tuning can de done to move things on even further – it really is an area that can improve the bike’s performance.

Springs and dampers.

Lighter, air sprung units are the way to roll when it comes to most trail and enduro bikes and like the matching forks up front they keep weight down and give ease of tuning the spring rate. Matched with good damping qualities these give a progressive quality to the travel of the shock.

For DH bikes we’re seeing an increase in air shocks as is the case with the dual crown forks up front. It’s a recent development however, so on most stock shocks on production bikes you’ll find a correctly weighted coil unit.

Sizes and fit.

With rear shocks, the sizes, tune and fittings will vary with each frame so it’s not as straightforward as with buying a fork. For years, shocks were sized with imperial measurements but recently we’ve seen a move to metric sizing – you’re looking a varying lengths of shock, with different strokes and fitments that can be specific to a frame. If in doubt seek advice from a dealer of your frame brand or a suspension centre.

Off-set shock bushings can be used to adjust the geometry and bottom bracket height of your bike and are an easy and cheap way of changing how your bike rides and handles.

RockShox Monarch Debonair is a well sorted shock for a trail bike.

TRAIL SHOCKS

A lightweight air sprung and oil damped shock with a compression lock out for climbing is standard kit on most short to mid travel trail bikes. A single air can with platform damping give good performance even when the shock is in the ‘open’ position – giving a good blend of traction and efficient pedalling – is the usual formula for success.

Adjusters will be a rebound dial and a two or three way compression/platform damping switch. Fox refer to this as CTD or ‘Climb, Trail, Descend’ – and the switch does what it says. Ideally the shock will be in a position on your frame where you can reach the lockout switch easily when needed.

Air springs should have a progressive action giving good small bump sensitivity (you’ll probably be running mid width tyres at a higher pressures) yet ramp up towards the end of the stroke. You’ve less travel to use, so a shock well matched to your frame and suspension layout is essential along with the correct air pressure and sag setting.

The standard Rockshox Monarch shock (pictured above) is standard on many well regarded trail bikes and this, or a Fox Float DPS are good choices. Air sprung X-Fusion shocks will show up on production bikes too such as the much anticipated 2017 Marin Hawk Hill.

ENDURO SHOCKS

As with the forks, moving from a trail bike set up to that of an enduro bike means adding a touch more ability and staying power but still keeping the weight low.

An air spring is pretty much standard these days for most riders looking at keeping an enduro bike below the 30 pound mark. Coils can still feature on a custom build usually, with riders coming from the gravity racing world – they still have their place and can add another level of suspension feel – but come with a weight penalty.

With 160-180mm of rear wheel travel on tap, this needs careful control and here we’re likely to see more damping adjustments and a piggyback style shock with an additional oil reservoir. Low and high speed compression damping adjustments become standard along with the usual rebound dial.

The Fox Float X2, Rockshox Monarch Plus and Bos Kirk all take this approach and the Cane Creek DB Air takes adjustment even further with low and high speed rebound damping dials too. This can take some knowledge, experience and patience so maybe not the one if you want the simple life.

So, a shock that can take repeated hits when pressing on hard in rough race conditions yet deals with slow speed control in the tight and twisty steep stuff. Supreme damping with enough mid stroke support so as not to upset the bike’s balance is the key here. Take some time to dial the settings in and the result should be impressive.

DOWNHILL SHOCKS

Now the serious stuff… To deal with the downhill riding, whether uplifting on local hand-cut tracks through to proper World Cup racing, a rear DH shock needs to be handle the steepest slopes, the biggest landings and provide a huge dose of grip to the rear wheel whether wet or dry.

Balance is required too. With long a wheelbase and very slack angles the rear shock also needs to keeps the bike’s poise and sit well with the chosen fork up front. Not too many years ago a rear air shock on a DH bike was a rare sight but now they are getting popular. The reliability, supple action and sure-footedness of a coil was always seen as the way to go but now a large can air shock, with a piggyback second chamber is man enough for the job. The RockShox Vivid Air is a good example or the Fox Float X2, which is standard kit on the YT Tues CF Pro, a 2016 Dirt 100 pick.

If you stick with the established world of the coil shock you’ll find that a stock bike should have an appropriate spring weight for an ‘average’ rider. This might not suit you, so even with some experimentation with set up you may need to budget for another spring. Most are steel, with lighter (and expensive) titanium options available; £30-£40 for a coil shock with ti running in at just over £100.

The Ohlins TTX, Rockshox Vivid coil and Fox DHX2 and Cane Creek Double Barrel coil are all choice shocks that we can recommend but also take a look at Marzocchi C2R and the Manitou Revox.

Get the right spring for your weight (if you’re going with a coil), the correct fit for your bike and a good understanding of the adjustments and you’ll have a starting point. This needs to go hand in hand with the front fork to work in a balanced manner.

If you’ve bought a production bike then be prepared to seek some expert advice to get the best out of your set-up and this really goes for all suspension units, whether forks, shocks, trail through to DH.

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