Suspension 101

As the weather improves and (hopefully) the Lockdown restrictions are lifted we can all look forward to getting out on our bikes again so in preparation for that I thought it might be helpful to set out some basic guidelines to setting up the suspension on our bikes.

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Now some of you may have already done this, but I’d hazard a guess the majority reading this have never done anything with their suspension, just accepted it as it is when the bike arrived, jumped on and gone for a ride. I know that was me (still is to a degree:confused:).

Regardless of whether the bike was brand new or used but new to you, it’s an odds-on favourite the suspension will not be set for you and your weight. Chances are, if its a bike that’s had previous owners, that someone may have ‘fiddled’ about with it in the past, maybe not knowing what they’re doing and you’ve inherited something that’s definitely not as good as it could be. You may even have a bike where the front suspension is not in sync. One of my bikes. when I got it and checked it, had different preload, compression and rebound settings on each of the front forks, no wonder it felt a bit weird.

At this stage I need to point out that this is not an article about how to set your suspension for track day or race use, or for motocross, this article is designed for the majority of us who ride our bikes on the road under normal conditions be that a Sunday ride out, touring across Europe or just going to the shops.

Why bother? Why not just leave things as they are, after all it seems OK.

The suspension is so important; it’s what keeps your wheels on the road, with the correct amount of pressure, when you go over bumps and imperfections in the road surface so the tyres can grip the tarmac. Its what keeps your tyres in contact with the road under braking, acceleration and cornering and it’s what makes your ride comfortable and enjoyable. If the suspension is not set correctly for you and your weight you run the risk that you are placing suspension demands upon the tyres rather than the suspension units; in the fully upright, straight ahead mode this may not be an issue but in the cranked over, cornering, mode this could be a serious issue as the tyre scrabbles for the grip it needs to keep you shiny side up. Also, you may feel you have an issue with your suspension that requires you to change out the unit(s), yet if the suspension isn’t set correctly for you how do you know it’s the suspension that’s at fault and not just the settings that are incorrect? You could save yourself a whole load of money.

Suspension components

In it’s simplest form the suspension is a spring that connects the bike (and rider) to the wheels. It suspends the bike above the axles. However, if it was just a spring then a bit like Zebedee after smoking one of Dylan’s cigarettes (and for those below a certain age who have never seen the Magic Roundabout you really ought to) it would just bounce up and down and be continually pogo-ing. Thus a form of damping has to be applied to slow down the compression and the decompression of the spring. In most road bikes the damping of the spring’s oscillations is done by oil, in a few it’s done by air, or an inert gas that can be compressed such as Nitrogen or a combination of the two. Regardless of how the damping is effected, in principle the way it works is the same.

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OhlinsShockSchematic.jpg


I don’t want to go into the intricacies and details of all the different variants of suspension internals that are available from the different manufacturers or even within a specific manufacturer’s range it is suffice, for the purposes of this article, to simply explain the following.

The spring compresses and relaxes as the bike moves over the road surface, as the spring is compressed, and the overall length of the housing for that spring shortens, a piston moves and exerts pressure on the damping oil. As oil cannot be compressed it gets moved from the main reservoir within the suspension to an expansion chamber, passing through a valve (NB this valve can be any one of a number of different designs). As the pressure is taken off the spring and the housing for that spring extends back to its resting position the damping oil is sucked back from the expansion chamber to the main reservoir, typically (but not always) passing through a second valve.

RaceTechUSDForkSchematic.jpg

The rate at which the oil flows through those valves controls the rate of compression and expansion of the spring. The rate of flow of the damping oil is affected by a combination of the viscosity of the oil and the nature and size of the valve it passes through and it is these two aspects that can be ‘tuned’ so as to control the movement of the spring.

The native rate at which the spring will compress and expand is determined by the diameter of the steel wire used to make the spring coil and the number of turns. Thinner steel coil and less turns gives a spring that’s easier to compress and vice versa.

The majority of motorcycle suspension uses linear rate springs which compress at an even rate over their entire length but some use progressive springs which have an increase in the number of turns at one end and thus as they move through their compression stroke more pressure is required to compress them.

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Linear spring
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Progressive spring


How to set the suspension for you.

First you need to set the ‘Sag’ which is the amount the bike settles under;
a) it’s own weight and
b) the weight of the rider and any pillion and/or luggage,

i.e. how much the suspension is compressed when those weights are applied to it.

You’ll hear and read terms such as ‘free sag’, ’static sag’, ’rider sag’, ‘race sag’, ‘total sag’ and others, unfortunately in researching this article it's apparent that different people and publications use them interchangeably and incorrectly. What may be called ‘rider sag’ in one source is ‘static sag’ in another, what is called ‘static sag’ on one is ‘free sag’ in another - most confusing. For clarity in this article I use ‘Static Sag’ as the term for how much the bike’s suspension settles under its own weight i.e. when it is static and I use ‘Rider Sag’ for how much the bike’s suspension has settled under the weight of the rider (and any pillion) i.e. where the suspension is when you are actually riding the bike and which, by the very nature of it, has to include the Static Sag.

Rider Sag is the important figure, Static Sag arguably is of lesser importance and really is no more than a guide to whether or not you have applied too much or too little preload or, more importantly, whether the spring in the suspension is suitable for your weight.

Too little Rider Sag i.e. the bike and rider don’t settle into the correct suspension range means the suspension could top out on acceleration and over bumps, too much Rider Sag i.e. the bike and rider settles too far down the suspension’s range, means the suspension could bottom out under braking and cornering. If the latter happens then the tyre begins to take over the role of the suspension and if it’s doing that it’s going to be struggling for grip at a time when you need all the available grip there is.

Before doing anything else at this stage make sure your suspension, tyres and the rest of the bike are in good working order. Make sure your fork and/or shock seals aren’t leaking, your rear shock’s linkage isn’t binding, your shock and forks compress and expand freely, your steering head bearings are in good shape and correctly torqued, your chain is correctly adjusted and your tyres have the correct pressure in them.

Next, you need to know the maximum length of travel of the suspension units front and rear. This information, if not in your bike owner’s manual, can usually be found on the internet, but do make sure it's a reliable source. The maximum length of travel will vary from model to model so do not assume they are all the same. For example, the suspension used on a Panigale R will have less maximum travel than that used on a MultiStrada. It’s important that you find out this figure because you need to set the suspension sag accordingly. All too often you will read articles, see videos etc., where someone says “your sag should be XX mm”, but I question, if they don’t know the total possible travel of that suspension unit how can they state with such authority what the sag should be? Not all bikes have the same suspension units so not all bikes will have the same sag settings.

On the basis you don’t want the suspension either bottoming out or topping out you ideally ought to have the suspension working for c.90% of the time within the middle third of its travel. If the suspension tops or bottoms out it cannot hold the wheels and tyres in full contact with the road and you are losing control. If it’s working for the most part within the middle of its travel you still have 1/3rd of its travel left at both ends for extremes. If you don’t know its maximum travel you can’t set your suspension to be in that sweet spot. The ideal Rider Sag setting therefore should 1/3rd of the max suspension travel.

The table below gives you some examples of total suspension travel: (do not assume similar bikes are the same).

BIKEFRONT mmREAR mm
Monster 1100S130148
998S120130
Multistrada 1200170170

Looking at the vast differences between these 3 bikes I just don’t see how anyone can say something like “oh, yeah, mate, your sag needs to be 25mm for the track and 30mm for the road”.

Using the M1100S as an example, in order to be just at the beginning of the suspension’s sweet spot the Rider Sag needs to be set to 43mm front and 49mm rear, i.e. the sag which results when you ride the bike as you would normally, be it solo, solo with luggage, two-up, two-up with luggage etc., and in your (and your pillion’s) full riding gear.

Measuring Sag.

Before measuring and setting your sag make sure the suspension, front and rear, has been put back to the factory default settings. Typically this information is in the owner’s manual and will set out how much pre-load, compression damping and rebound damping (where applicable) was applied by the factory. You need to do this in order to a) set a base point and b) make sure where suspension is paired, e.g. the front forks, they both have identical settings. An example of how these settings are presented in the owner’s manual is below.
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Sag is then measured from the axle to a point on the bike. For the front suspension it’s typically from a point on the front wheel axle to a point at or above where the fork tubes meet and slide into each other (assuming USD forks - if your forks are not USD then measure to a point on the triple clamp). Wherever that point is make a mark and make sure you use the same point each time you wish to check or adjust the sag.

To measure sag you will need either;

a) a tape measure and a friend with good eyesight who will be consistent in the angle they view the tape measure at so as to avoid any parallax and be mm precise in their readings plus possibly a second friend to help hold and lift the bike for the steps where you’re sitting on it, or,

b) a wheel chock and a tool such as the MoTool Slacker* which permits consistently accurate readings to be obtained single handedly.

For this article I’m using the MoTool Slacker so I can do it on my own, consistently, and don’t have to impinge upon someone else’s time. Additionally the current version of the Slacker comes with a very useful phone App that controls the Slacker, displays the readings and records them on a bike by bike basis.

Front suspension.

With the bike in the wheel chock, steady and secure, bounce the front of the bike up and down to get over any stiction and have the bike settle under its own weight. Now attach the Slacker to the front axle, or if using a tape measure and friend(s) mark a point on the axle from which all future measurements will be taken. Select a point on the fork leg (at or above where the forks slide into each other) or the triple clamp and, depending which tool you’re using, either attach a Slacker hook, the Slacker fork tube bracket, or make a mark to which you will be measuring with the tape measure. Now extend the Slacker cord and attach it to the hook (for those with a tape measure measure between those two points and make a note of the measurement).

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If using a tape measure we’ll refer to this as measurement A.

If using the MoTool Slacker simply initiate the AutoZero function, the tool and the App will now indicate you need to lift the front of the bike to take the weight off the front wheel and top out the suspension. The Slacker will set the maximum length as zero.
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If using the tape measure method lift the front of the bike and have your friend measure the new distance from wheel axle to marked point and make a note of it, we’ll refer to this as measurement B. Under this method measurement B less measurement A = the Static Sag, make a note of it.

Now let the bike settle again on its suspension - the Slacker will now indicate the Static Sag of the bike (and if using the tape measure it will be back to measurement A).
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Repeat the process 2-3 times to ensure you get a consistent reading; this overcomes any stiction in the suspension components.

Now in full gear, i.e. all layers, protective clothing, boots, gloves, helmets, airbag whatever else you would normally be wearing when riding (inc pillion and loaded luggage if preparing for a tour) sit on the bike in your normal riding position, feet off the ground and on the pegs. It is important you are in your full riding gear and not just in t-shirt, shorts and flip-flops because your riding gear can add as much as 15-20Kg/person to the overall weight upon the bike, which as a percentage of your body weight is very significant.

Once the bike has settled and the suspension compressed save the reading in the Slacker App. This reading is what is referred to in this article as the Rider Sag i.e. how much the bike and rider compresses the suspension.
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If using a friend and tape measure then make a note of the new measurement, we’ll refer to this as measurement C.

For the tape measure method it is B less C which is the Rider Sag.

Whichever method you’ve used the Rider Sag should be 1/3rd of the total possible suspension travel.

In the example of the M1100S the target figure is 43mm being 1/3rd of the total front suspension travel of 130mm. As can be seen the actual Rider Sag on this bike is 35mm and therefore needs to be adjusted to the 43mm target.
(NB. The suggested figures for Static and Rider Sag i.e. 12mm and 35mm +/-5mm, in the Slacker App as displayed above are incorrect for this bike and need to be updated.)


Adjusting Sag.

You may be lucky but chances are the Sag you have measured is not where it should be so now the suspension needs to be adjusted to bring it to that point. This is where preload comes into play. Preload is an amount of compression that is applied to the spring before the spring compresses under either the bike’s weight or the weight of bike and rider. If your Rider Sag is too much i.e. more than the target then you need to increase preload to the spring and if your Rider Sag is too little then you need to reduce preload. Be aware though that adding or reducing preload from the factory default alters the geometry of the bike, probably not so much that you’d notice it on the road but those that use their bikes on trackdays may very well notice the smallest difference. Reducing preload (and adding Sag) will lower the ride height, adding preload (and reducing Sag) will increase the ride height. The reason this happens is explained at the end of this article.

At this stage, whilst still sitting on the bike, in all your gear with your feet off the ground, start to adjust the preload settings to bring the reading on the Slacker App on your phone in front of you to the desired level. If you’re using a tape measure and your friend is still willing and able to assist then have them read out the incremental mm changes as you adjust the preload until you get to the desired figure. Remember to adjust both forks by the same amount.

insert adjusted Sag screen shot here.

When you get off the bike the Slacker measurement will revert to the Static Sag (remember we used its Auto Zero function to detect when there was zero compression in the suspension).


Rear Suspension

The rear suspension is done in a similar fashion to the front. First set the suspension settings i.e. preload, compression and rebound (if you have them) as per the owner’s manual. Next attach the Slacker to the rear axle and select a point on the frame directly above the Slacker. Try not to use any of the body plastics or seat at that point as they can move enough on their fixings to the frame to prevent you being consistent in your measurements. If using a tape measure mark up your datum points.

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Set the Slacker to Auto-Zero and lift the rear of the bike so the shock tops out. As with the front, repeat 2-3 times to overcome any stiction and get a consistent reading. Now let the bike settle under its own weight and the reading from the Slacker is the Static Sag at the rear, save that or make a note of it using the tape measure method.

Again, sit on the bike (in full gear) and let the suspension compress further under your weight. Record the reading on the Slacker which is the Rider Sag i.e. the amount the rear suspension is compressed when you are on the bike ready to ride. Compare this figure with your target figure.

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If the Rider Sag is too high then reduce the preload on the rear shock spring(s), if the Rider Sag is too low then increase the preload until the target Rider Sag is achieved.

Save the preload settings front and rear for future reference.


Compression and Rebound damping.

This is what controls the rate at which the spring compresses and expands. Compression damping controls how quickly the spring can be compressed and rebound damping controls how quickly the spring returns to its resting position, combined they inhibit the constantly diminishing oscillations that would otherwise occur in the spring after a compression i.e. the pogoing effect.

Most modern suspension units are fitted with a means to adjust either compression or rebound damping or both. Some cheaper suspension units may not have any any means of adjusting these in which case the only way you can increase or decrease the effect of the damping is by changing the viscosity of the oil within the suspension unit.

Check your owner’s manual to find exactly what you can adjust and how those adjustments are made for your bike.

Typically, on the front suspension (assuming it’s USD) the compression damping is adjusted via a screw at the base of the fork leg and the rebound damping is adjusted via a screw at the top of the fork.

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Rebound damping adjuster screw set within the preload adjuster (red)
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Compression damping adjuster screw at bottom of fork leg

If you’ve not done it already then in the first instance set the adjustments as per the owner’s manual. Screw the adjuster (clockwise) all the way in then screw it (anti-clockwise) out the recommended number of ‘clicks’ or turns.

Rear suspension units come in a variety of different shapes and models so consult the owner’s manual to find out exactly where and how you make the adjustments, again set them to the manufacturer’s recommended settings.
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Compared to Sag setting, compression and rebound are not measurable and are much more subjective. Having set the Sag and put the damping at the recommended settings you now need to ride the bike to see how it feels to you. What is your impression, not anyone else’s. Pick a route that you know and can ride around to test out the new suspension settings, don’t ride like Marquez, ride at a rate that allows you to focus on what the suspension is doing. Does the front compress too quickly and too much when the brakes are applied? Does it rise too much and the back squat down to much under acceleration? Does the ride feel smooth or can you feel every single road bump through the bike and handlebars? When you come off the brakes how quickly does the front come back to it’s median position?

Make a note of how many clicks or turns you make, and with regards to the front forks always make them equally to both fork legs, but play around with the compression and rebound settings. Apply the maximum amount of damping and see what its like on the road. Apply the minimum amount of damping and see how that compares over the same route. Then adjust the damping to somewhere in the middle that you feel suits you best and record the settings.

Remember all of this, i.e. sag & damping, is all subjective, once you have an understanding of what’s what, play around with it to get a setting that works for you, your bike, the way you ride and the roads you typically ride that bike on. There are no definitive answers to any of this.


Finally (for now) a few points to note about preload
.

When preload is applied to a spring it does not change the rate at which that spring compresses it just changes how much of the spring can compress when in use. i.e. if its a 100 N/mm spring it will need 100 Newtons of force to compress it by 1mm (100 Newtons is c.10Kg so if a 90Kg rider sits on that spring it will compress by 9mm) preload eats into the maximum amount the spring can compress. The more preload you add the less compression you have available in the spring to absorb the bumps, hence a suspension unit that’s had the preload wound up to the maximum is going to feel really harsh when ridden as the amount of compression of the spring has been so severely reduced there’s very little left to absorb the bumps of the road and more of those bumps get passed through to the bike’s frame and rider.

No suspension manufacturer will create a unit where the preload can be wound up so much there is zero travel left in the spring, the available maximum preload will usually take up no more than a small fraction of that spring’s maximum compression, but if you find yourself in a situation where you need to apply maximum preload to the spring(s) in order to achieve the desired amount of Rider Sag then it’s time to consider the fact you need a heavier duty spring. Conversely if, in order to achieve your desired Rider Sag, you have to have zero preload on the spring then you need a lighter duty spring.

Lastly, for now, with regards to preload I mentioned earlier in the article that increasing the preload will alter the ride height of the bike and thus the steering geometry. Increasing the preload increases the ride height and decreasing the preload decreases the ride height. This may seem counterintuitive at first because the first thought is that if the spring has been compressed as the preload is increased then the length of the suspension should also decrease. However, what actually happens, thanks to the laws of Newtonian physics and the fact that for every application of force there is an equal application in the other direction, as the preload adjuster pushes down on the spring to compress it, it also pushes up against its retainer within the suspension and thus increases the length of the suspension (see diagram). It is for this reason that increasing the preload reduces the amount of sag, for if you put 50Kg of preload on the spring that equates to 50Kg pushing back up at the weight on it, i.e. you and the bike.

PreloadExampleLAL.png

Thus it is possible to alter your ride height, front and rear, by adjusting the preload on the springs. However, be aware that altering the ride height will also alter the geometry of the bike and thus the way it handles, noticeably with regards to the front suspension the way it turns into corners and picks up on the exit from corners. Note also that as the preload is altered, the ride height alters and the available suspension travel alters which will have an effect upon the target Rider Sag you want. For the road this is not really an issue but for the track it becomes an issue and is a little more complicated and hence why I’ve not covered track day suspension in this article

You can find some further explainations here

Remember - Reducing preload = adding sag; increasing preload = reducing sag.


The MoTool Slacker is available from @Exige




Acknowledgements
Life at lean
Cycle World
Ohlins
Showa
RaceTech
Motool
 
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Char

Elite Member
Subscriber
Brilliant and why I spend £40 and get someone to do it for me 😬

planning on going to MH Suspension soon to get my new bike sorted however the dealer has said

Don’t adjust the front suspension through the forks at all. The bike has very sensitive IMU’s which have been reset and calibrated to your suspension set up. Should they adjust this, the traction control system will throw a fit and show errors.

Thoughts ?
 

Noobie

Elite Member
Subscriber
Thanks for doing that Paul (y)

I must admit to being one of those who has tended to fit better quality brake pads, better brake lines, better tyres, better lighting but rarely have had the suspension set up different other than as it came to me.

Being more suited to be a prop in a scrum, I did once some moons ago, have the gixxer 750 k7 taken to a specialist and they set up the bike using standard suspension and the differences were very noticable in a positive way and for a very small sum of cash.

I appreciate some go further and then delve into aftermarket suspension upgrades but if you are going to spend cash on your bike, then for very little cash, a good suspension specialist can improve your bike greatly on the standard kit fitted.
 

West Cork Paul

Elite Member
Subscriber
Brilliant and why I spend £40 and get someone to do it for me 😬

planning on going to MH Suspension soon to get my new bike sorted however the dealer has said

Don’t adjust the front suspension through the forks at all. The bike has very sensitive IMU’s which have been reset and calibrated to your suspension set up. Should they adjust this, the traction control system will throw a fit and show errors.

Thoughts ?
I can’t help with electronic suspension as I’ve no experience of that and haven’t researched it yet but I’m sure there are others on here that can.
 

Expat Jack

Elite Member
Subscriber
Just set it to manual and it’s the same but with electronic clickers. You need to set sag in the normal way even with electric suspension.
Just to clarify on Ducati’s it’s either set as Dynamic or Fixed. Dynamic is electric and gives a small range of adjustment within predefined parameters eg 5 levels of compression between, say, 1 - 5 soft to hard. Do you can tinker with the suspension within preset parameters.
If you go into the Fixed menus you get something that resembles a normal setup with up to 30 ‘clicks’ for comp & rebound. So it’s still electric but you define the setting rather than leaving it to the pre set parameters of soft - hard.
I ran my V4s in fixed mode and it was miles better than the Dynamic settings. Even the steering damper has a massive range of settings and, out of the box, was far too stiff for my liking.
 

Markduc

Well-known member
Subscriber
@West Cork Paul How well does the app work, is it simple to use , connects easily through Bluetooth
does it let you set sag without assistance
would it work better if you used snap on tools :unsure:
 

West Cork Paul

Elite Member
Subscriber
@West Cork Paul How well does the app work, is it simple to use , connects easily through Bluetooth
does it let you set sag without assistance
would it work better if you used snap on tools :unsure:
The App works seamlessly. Simply open the App and then turn on the Slacker it connects automatically to the App and the reading then appears in the App (as well as on the Slacker at axle level).

Yes you can set sag without assistance as for the front suspension you simply sit on the bike snd adjust the preload and watch the sag on the screen change accordingly.

For the rear you obviously need to hop off if on your own to do it but then as you have the Static Sag reading in the App you just adjust the preload to adjust the Static Sag then hop back on and check your Rider Sag has changed by the correct amount.

You can also record the damping adjustment and any other notes you want in the App so you never forget (or lose the piece of paper you wrote them down on) your settings.

For the record I used a 17mm Draper ratchet spanner to adjust the front and the Ohlins spanners for the rear. They’re all I had to hand so I couldn’t test whether a Snap-On (or Halfords) tool might be better. I’ll have to get some and let you know 😁.
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The GOAT

Administrator
Staff member
Posts that do nothing to contribute to this article have been hidden from view. Please only post something that contributes, be it a correction due to inaccuracy of the authors article or be it adding further information which will help others.
 
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