The Basics

By:James Siddall

Sorry, but its true. The basic stuff is some of the most important. So let's review some of the key things that need checking to optimize suspension performance.

Steering head and swing arm bearings
I know, super basic, but if they are loose or worn, your suspension will never feel good, so humor me, and check them.

Inches
Stop using these. Millimeters are much easier to measure and calculate with.

Counting
I know basic huh? But if we are all on the same page it saves a lot of headache.
Clickers are counted from fully closed (commonly referred to as full hard, or FFH for short)
Completely close the clicker, by gently turning it clock wise in most cases, (some older WP PDS shocks being the exception), and then count out with the first click of any sort being one.
Preload is the only thing you measure the opposite way,winding it all the way off, then starting with zero, and counting actual millimeters of preload.

Fork Pinch bolts
It is critical that these are not over tightened, especially on the lower triple clamp. They will cause serious binding if they are over tight.

Axle pinch bolts
Same here, if these are over tightened they can bring all kinds of harshness back into your fork. Check the spec.

Preload
Preload is quite literally, the amount your springs are compressed when installed. By measuring the difference in length of the spring before you put it on (free length), and the length of the spring as it sits on the shock (installed length) you can determine the preload. Some specs will call for a certain amount of preload. Otherwise you can use the sag to determine the appropriate amount of preload.

Static sag ( or free sag )
This is the distance in millimeters that the bike settles under it's own weight. It is important to the suspension function that the bike retains some static sag in most cases.
Normally the free sag is between 5% and 10% of the total travel.

Rider Sag (also sometimes called ride height, one G, or race sag)
This is the amount the bike settles with the rider on in riding position. Many Off-road setups will specify only a total sag number, generally between 90 and 110mm.
The general rule of thumb is that the sag should be 25% to 33% of the total available travel.
If you are unable to get the total sag number you seek without either too much or too little static sag, you will need to change springs.
We will be happy to recommend one for you.

Clicker settings
Most settings are designed to work within a window of clicker positions. If you find you have to change the position dramatically to improve performance, and are still not happy with the results, it is generally a cry for help from your valving. Stock valving has to cater to a wide range of riders and ability levels, and can't be expected to be right for everyone. A revalve should be able to get you in a range where we can fine tune for conditions with the clickers.

Compression
The compression clicker is a low speed adjustment that affects how quickly or freely the suspension compresses. By low speed, we mean low shaft speed, or slower movements of the suspension. Faster movements will quickly overcome the clicker, and be controlled mainly by the reaction of the valving shim stack. This is what we tune when we revalve. The stack also has influence on low speed movements, but the clicker is fairly exclusively low speed. With this in mind it is important to remember that it is really easy to make an off road bike overly harsh with the clickers in to tight, and a road race bike lose grip with the compression clickers in too tight. So proceed carefully, and realize that if you need to deviate from the standard clicker setting by a great deal, the shock or fork spec is probably not as good as it could be for you.
If we have done your suspension you should have received it back with a rubber o-ring on the fork leg. This is meant to show you the maximum stroke used. Keep an eye on it when trying to perfect your fork settings.

Off Road

Fork:
As mentioned, too much clicker makes the forks harsh on small bumps. Turn the clicker out till they are as plush as they can be. Occasional light bottoming is ideal as this means you are using all the intended stoke, giving maximum plush ness.

Shock:
The same principles apply for compression clicker settings on the shock. Occasional light bottoming yields maximum plush ness. Bottoming can be controlled by turning in the clicker, but be careful of making it harsh on the small bumps. Softer is better, for grip and comfort except in soft rolling whoops or G-outs and sand. (Where the opposite is true)

Roadrace/Street

Fork:
Too much compression damping will prevent adequate weight transfer to the front, and make the front push, feel vague and want to run wide. Small bumps will be harsh as well. Too little and you will bottom it too easily, and you may find it gets low on the brakes, moving towards a tuck the front sensation.

Shock:
Again, too much brings harshness over the bumps, but also prevents adequate weight transfer to the rear, reducing available grip. And as we know, in road racing it's all about grip. On the street we may have grip to spare, but who wants to ride a harsh bike around all day. Too little compression control will bring a sloppy wallowy feeling especially when trying to quickly flick the bike on its side, or change direction.

Rebound:
The same is true for the rebound clicker, and in fact it is just as easy to make a real mess of the suspension function by running the clicker in too tight. The rebound controls how quickly the suspension returns from being compressed. Slowing the rebound with the clicker will hold the suspension down; this can allow it to "pack down" over a series of bumps, or in the case of a road racer to abuse the tire overly. Conversely too little rebound will give the bike a wallowy feeling and diminish a rider's confidence at speed.

Off Road:

Fork:
Aside from packing harshness over a series of bumps, excessive rebound can hold the front down on corner entry leading to a tuck. Insufficient rebound will prevent enough weight on the front for good grip, with the front popping up and pushing wide, or climbing out of a berm.
Shock:
As we have said, packing down is the number one trouble with excessive rebound. If the back won't track straight through a series of whoops, or if it kicks excessively over logs, the rebound may be too slow. Too slow of a rebound setting can also hold the back down over acceleration chop and makes the bike feel rough.

Roadrace/Street

Fork:
The front rebound setting is most noticeable in the transition between the entry and middle phase of the corner. Insufficient rebound makes it difficult to get off the brake lever when trail braking as the front will feel like it wants to unload and push off wide. Conversely, too much rebound can leave too much weight on the front, and make the bike feel nervous, and even leading to a tuck.

Shock:
Road bikes suffer from the same difficulty with packing over a series of bumps that off road bikes do, though the bumps are usually less intense. One of the biggest drawbacks to excessive rebound in a road race bike is accelerated tire wear as the rebound holds excess weight over the rear.

Springs and Preload
If we have set up your suspension for you, it is very likely we will have recommended a spring for you and a window of adjustment with the preload. Preload is necessary to hold the bike up in the position the designer had in mind when he planned it in the first place. If the springs have been chosen correctly, they should yield our baseline sag numbers, while maintaining some static sag. As mentioned earlier we like to see around twenty five to thirty percent of the wheel stroke as sag, with five to ten percent of the stroke as static sag.

Preload is often used as a tuning variable, but like with anything it is important to avoid going to extremes. It is not uncommon to find preload used to band-aid other conditions.

A common problem includes the use of too much preload to band-aid an under sprung or under damped fork. The problem that then arises is that the bike is held high up in the stroke all the time, adversely affecting weight transfer, and sometimes steering. The bike will also tend to want to quickly pop up in front when the brake is released. This is very problematic for effective trail braking.

Springs

Sag:

Here is the deal with Springs and Spring Force:

Springs are rated in one of three different numbering conventions.
Either lbs per inch, Kilograms per millimeter or Newtons per millimeter.

KTM springs are all rated in Newtons.

The Standard KTM spring rates are 4.8 Newtons per mm in front, and 150 Newtons per mm (STD) or 140 Newtons per mm(S).

This is why your spring is marked 140-225 or 150-225, these numbers are the rate (in Newtons) and the length (225mm).

Now onto the good stuff:

When you compress a linear spring 1mm, you will store force in the spring equal to it's rate. This applies to any millimeter of compression, whether it comes from preload, a riders weight, or a bump in the road. The spring doesn't care, it's a spring, it's got bigger problems.

So knowing this, lets do a bit of analysis on our 950. The Stock Spring is a 4.8N/mm spring. The stock Preload is 17mm assembled. Why did I say assembled you ask? Good Question. When fiddling with Preload adjusters on the outside of a fork, it is important to remember that when the fork was assembled, in most cases it was put together with some preload already on the spring, often in the form of spacers. When you turn the external adjuster, you are simply adding to this total. So to do the math , we need to know the total preload, not just the external.

So, we have 17 times 4.8 = 81.6N of force stored before we take the bike off the stand.

Now we drop the weight of the bike on top of this poor spring, and as you probably guessed, 81.6Newtons of force is not going to hold our 950 all the way up, so our spring will sag some.The sag of the bike under it's own weight is the Static sag. This sag compresses the spring further. Let's say in stock trim the bike sags 50mm under it's own weight. Add 50mm of spring compression at 4.8N per mm = another 240N of force stored. For a total 321.6N of force. Now knowing the spring rate, the preload and the sag, we can change any of these variables and calculate the others with the following formula:

Spring Rate*(Preload+Sag) = Load (as we just explained above)

4.8*(17+50)=321.6

Then to calculate the required change in preload should you change the spring:
(Load/new spring rate)-sag = new preload

Or the change in sag if you change the preload:
(Load/new spring rate)-new preload = new sag

Keep in mind that you can use this calculation for Static sag or for Total(commonly called Race) sag. But you cannot mix and match. One or the other only please.

Sag diatribe authored by Burnt Guy James Siddall @ www.superplushsuspension.com