Everything you need to know about how to set up mountain bike suspension
Not many riders know how to set up mountain bike suspension. We all have it but not that many of us know how to set it up. We’ve lost count of the number of times we see riders out there on the trail with poorly set up suspension.
The majority of riders have incorrectly set up suspension. Become part of the clued-up minority by following this guide to setting up your suspension.
We’re covering both suspension forks and rear shocks. Here’s what this guide covers…
- Basic suspension theory
- Setting your sag
- Setting your rebound damping
- Setting your compression damping
- Adjusting your spring progression
- How to look after your suspension
How to set up mountain bike suspension
Setting up suspension is not easy but it’s not hugely complex either. You can do it. Take your time. Don’t do it in a rush in the car park before a ride.
With setting up suspension you are essentially setting two things: how hard the spring is and how that spring’s movement is controlled.
Adjusting how firm the spring is
On coil sprung suspension, how firm the spring is is dictated by the coil spring used. If you need a harder or softer spring, buy a new coil spring. That’s it.
Using a spring that’s too soft (ie. too low a air pressure) will result in suspension that wallows about too deep into its travel and bottoms out over eagerly.
Using a spring that’s too hard (too much air pressure) will result in a harsh ride that never gives out a suitable amount of travel.
On air sprung suspension (which is the vast majority of suspension these days), how firm the spring is is dictated by air pressure. Air pressure in an air chamber. If you need a harder or softer spring you adjust the pressure in this chamber with a shock pump.
For this guide we’re going to assume that you have air sprung suspension but if you do have coil sprung suspension this guide is still worth reading as the principles are still relevant.
Adjusting how the spring’s movement is controlled
The spring’s movement – how it compresses and how it re-extends (rebounds) – is controlled by your suspension’s damping.
Damping is essentially fluid passing through a hole. With a small hole to pass through fluid will move through slower. With a larger hole, fluid will pass through faster. When you’re adjusting your damping you’re adjusting the size of hole(s) that fluid flows through.
How much control and adjustment you have over your suspension’s damping will depend on your fork or rear shock. Some forks and shocks only have rebound damping adjustment. Some forks and shocks have compression damping adjustment as well.
Some higher end forks and shocks have separate damping adjustments for low speed and high speed impacts/forces. We’ll deal with these later on in this guide.
Setting your sag
This is first thing you need to do with your suspension. Thankfully it’s also the easiest thing you’ll need to do.
What is sag? Sag is how much your bike settles into its suspension when you get on your bike and take your feet off the ground.
Suspension is designed to work best with between 25%-33% sag (AKA a quarter to a third). For example, on a 100mm travel bike you want to aim to have 25mm-33mm of sagged travel when you sit on your bike.
In our experience it’s best to set your sag whilst standing up on the bike. You’ll need to lean against something, such as a wall. If you set your sag whilst being sat down your rear shock will end up being set too firm and your fork will end up being set too soft.
Wind off all your rebound and compression damping (if you have it) to the minimum settings. You don’t want the damping interfering with setting your sag.
Slide your suspension’s rubber O-ring travel marker down to the seal.
Stand up on your pedals whilst leaning lightly against a wall (or tree, or van etc). Try not to jerk or bounce around whilst doing so, or whilst getting off your bike.
Once off your bike, measure with a tape measure how far your O-ring has moved from the seal.
With forks this is straightforward. How far the O-ring has moved in mm can be quickly worked out as a percentage of the fork’s overall travel.
Warning: in our experience forks can be resistant to sagging, so avoid setting more than 20%-25% sag or else it’ll end up being to saggy-soggy when out on the trail.
With rear shocks it’s a bit more complex because a mm of O-ring travel does not equal a mm of rear wheel travel. You’ll need to measure the stroke length of your shock (how much shaft is showing at full extension, eg. 50mm stroke). Then measure how many mm your O-ring has moved under sag. Then you’ll divide your stroke length mm by your sag mm.
For example, on a rear shock with a 50mm stroke, running 12.5mm of sag, means it has 25% sag.
Use your shock pump to inflate or deflate the suspension until you are getting 25% sagged travel (25% is the best starting point in our experience as most bikes are designed around having 25% sag).
Once riding, if you find you’re not getting decent amounts of travel used on big hits and landings then feel free to try increasing how much sag you’re running ie. let air of the suspension, try 10psi at a time. You should also dial off a click or two of rebound damping after you’ve let air out.
Setting your rebound damping
DO NOT attempt to set your rebound damping until you have set your sag properly.
Rebound damping is what controls the speed at which your suspension re-extends after compressing ie. after absorbing a hit.
Not enough rebound will make your suspension pogo around and ricochet wildly off big hits.
Too much rebound will cause your suspension to pack down resulting in a harsh ride. It will also foul up your bike’s geometry and thus handling.
Whilst rebound can be a personal preference thing – some riders like ‘fast’ suspension, some prefer ‘slower’ – there is definitely a correct spectrum to be within.
To set your suspension’s rebound damping, find a kerb.
Dial off all your rebound damping to minimum.
Ride off the kerb, stood up on the pedals, at slow to mid-paced speed. Your suspension will probably compress, quickly re-extend (past the sag point), compress again and then re-extend again. In other words, it’s bouncing around like a trampoline.
The aim here is to dial on rebound damping until this trampolining effect is minimised.
Dial on a couple of clicks of rebound. Ride off the kerb again. Keeping adding rebound clicks until the suspension is only re-extending once after compressing.
Once out riding, if you then feel that your bike is packing down and riding too deep into its travel, dial off a couple of clicks of rebound.
Setting your compression damping
Not all suspension forks or rear shocks have adjustable compression damping so this section may not be applicable to you.
If your suspension does have adjustable compression damping, you don’t HAVE to adjust it if you feel it might be a bit beyond you at the moment. that’s fine. Go ride your bike.
Compression damping affects how your suspension compresses.
Not enough compression damping will result in suspension that bobs around and dives through its travel on descents and/or under braking.
Too much compression damping will prevent your suspension from absorbing impacts effectively. You’ll feel it kick back at you, also known as ‘spiking’.
Compression damping is again, a thing of personal preference. Some riders like an easy-moving supple suspension, other riders prefer super stable suspension that doesn’t move eagerly. Think firmly-sprung rally car versus cushy family estate car.
Generally speaking, a lot of riders don’t have enough compression damping dialled on. Their suspension bobs around and dives excessively.
Preset compression damping modes
A lot of rear shocks (and some forks) have built-in presets for compression damping. Fox forks and shocks, for example, often have ‘Climb’, ‘Trail’ and ‘Descend’ settings.
Climb mode means lots of compression damping, resulting in a firm ride that resists moving under pedalling (bobbing) but doesn’t give up sufficient suspension travel on bumps.
Descend mode means minimal compression damping, resulting in a supple, plush ride but one that can be wallowy with excessive bobbing.
Trail mode is the general all-rounder setting. Firm enough to avoid excess bobbing but still able to absorb decent hits.
RockShox and other companies have similar presets but often it’s limited to two settings ie. firm and open.
Low speed compression
If you have suspension with properly adjustable compression (as opposed to built-in presets) then it’s worth getting to know how it works.
Basically low-speed compression affects how the suspension compresses at low speeds and during low amplitude forces.
Dial in low speed compression until your suspension doesn’t bob about excessively under pedalling. Some bob is fine (often unavoidable really) but it’s nice to get rid of your suspension pogo-ing around robbing you of energy and control.
Don’t worry about losing small bump absorption too much; your tyres are there for soaking up the small stuff.
With low speed compression dialled in suitably you’ll also find that your fork doesn’t dive or sink through its travel during steep descents, especially those where you’re braking significantly.
High speed damping adjustments
Not a lot of suspension forks or rear shocks have adjustable high speed damping (rebound or compression). It’s reserved for high end units intended for knowledgable riders and racers.
Setting high speed damping is something of a dark art. Most riders dial off the high speed compression. They also dial in a few clicks of high speed rebound if they’re riding terrain with lots of jumps and drop-offs.
We’re not going to go into adjusting high speed damping in this guide. If you have a shock with high speed damping adjustment, your best bet is to refer to the instruction manual and/or website of the manufacturer.
Adjusting your spring progression
Believe it or not, on a lot of suspension nowadays you can have it behave in a certain way for the first part of its travel whilst at the same time have it behave in a different way for the latter stage of its travel.
In other words, you can have a supple, linear rate action for the first third (approx) of your suspension’s travel and also have a firmer, ramping up action for the latter third of your suspension travel.
This tweaking of your suspension’s spring rate is done via volume spacers.
Inserting volume spacers into your fork (eg. RockShox’s Bottomless Tokens) or rear shock only affects how your suspension feels for the last part of its travel. How the suspension behaves at the sag point or in the middle part of its travel remains unaffected.
If you’re a lighter rider, or a rider who rides relatively sedately on milder terrain, you’ll be fine with your suspension as it is. You don’t nee volume spacers. Just ride your bike.
If you’re a heavier or more aggressive rider tackling technical terrain at high speeds then you can really benefit from increasing the progressivity of your suspension.
With volume spacers installed you can run lower air pressures in your suspension and/or less low speed compression damping and have a supple freely-moving action to the early stages of your suspension’s travel whilst at the same time avoiding a fork that blows/dives through the latter stage of its travel too eagerly.
And finally, look after your suspension!
Don’t neglect your suspension. It will degrade depressingly quickly if you do, especially in filthy conditions. This is more true for forks as it is for rear shocks (although you should still keep an eye on your rear shock).
You’ll be surprised how easy and quick it is to perform a basic clear-out and lube-up job on your fork and rear shock.
You probably won’t need any weird specific tools but you will need to get hold of some suspension fluid that is designed for your particular brand of suspension.