Thursday, November 6, 2014

Setting your fork sag
First you need to measure the sag in the same way I described in my last blog post.  Your forks should sag between 1/4 and 1/3 the distance of your full suspension travel, which you will need to look at your bike’s specification sheet to find out that number.  As an example, if you have 10” of total fork travel, your total loaded sag should be between 2.5” and 3.3”.

As a guideline, you can use these numbers :*

                                Road Race           Street                   Dirt (full size)
Sag                         25-35mm             30-35mm             60-75mm
Preload                                5-25mm               10-35mm             3-15mm
Stiction Zone      5-15mm               5-15mm               10-25mm

*Race Tech’s Motorcycle Suspension Bible, Paul Thede and Lee Parks

In order to adjust the sag, you will need to remove the fork caps to gain access to the springs.  You adjust the sag by adding to or removing length from the spacers between the springs and the stops.  Each fork configuration is different, so consult your manual.

If you need to add more than the preload spacer lengths mentioned above to achieve the correct sag number, your springs are too soft and need to be replaced with the proper spring rate.  And in the same way, if you have to remove more than the recommended preload amount to gain the correct sag, your springs are too stiff. 

It is important to note that these spacer lengths are important.  Springs, in order to function correctly need to have some preload on them even when your suspension is fully extended.  And in the same way, you cannot correct for a spring that is too soft by adding a bunch of preload.  A .48kg/mm spring is still a .48kg/mm spring no matter how much preload you cram on top of it.  Springs are relatively cheap and the reward you get for a properly handling motorcycle will be worth it each time you let the clutch lever out to start on a ride. 

Spring selection

Now that you know how to measure and set your sags, in most cases on bikes where the rider is over 180 lbs or under 160 lbs, you will need to swap springs.  Most bikes are set up from the factory for a 165-170 lb rider.  (I wish I fit into that demographic)

There are some online spring calculators but please take those numbers with a grain of salt.  I have found some of the more popular calculators provided by my competitors to be very far off, especially for dual sport and adventure bikes.  Contact me and I can get you the right number of the spring rate you need.  You can either purchase the springs from me, which is of course my hopes, or take that information and source your own springs from your favorite source.

Sasquatch Suspensions has a large rage of springs available to you as well as being able to have custom springs made for your project.  Email me with your specific needs and I will get a quote to you.

Stiction Zone

What the heck is a stiction zone?  It was actually coined by Paul Thede, an engineer and the owner of Race Tech Inc.  It is a way of measuring how much friction is within your suspension.  This is how to do it.  When you measure your unloaded sag, have your helper lift up on the suspension and just let it settle.  Write down this measurement.  Then have your helper press down on your forks, compressing them, then gently releasing them and measuring where it stops.  The difference between your higher length and your shorter length is your stiction zone.

Friction is all around us, and I am not just talking about your boss.  In simple terms, it is the resistance to movement.  Friction can be a good thing, like how a tire uses friction to gain traction on the road surface.  But in other areas great lengths are traveled to minimize friction, like inside your engine, or within your suspension.  There are points that generate friction all throughout your suspension.  Seals, bushings, bearings, pinch points, etc., each adding a small amount of resistance to the smooth movement of your suspension.  When you add those small resistances up, it can actually become quite noticeable and affect how your bike handles.

Here is a simple test to show you what I am talking about.  Stand beside your bike with it off of the side stand.  Apply the front brake.  Slowly press down on your handle bars to compress the forks.  You will notice that at first the forks do not move, but as you add force, at some point they will break free and start compressing.  This is friction keeping you from compressing the forks until the force of friction resisting movement is overcome by the force you are applying on them.

Friction in forks comes from the bushings and the fork seals/wipers and you can never completely eliminate it. Friction can also come from damage to the forks like from a bent fork tube. As a suspension tuner, I have spent a lot of time looking for ways to minimize this friction.  One process that I have been using with great success is to actually hone the fork sliders putting a fine cross hatching pattern in the chrome coating.  This microscopic texture traps oil in the grooves which lubricate the bushings and seals better as well as breaking the hydraulic seal between surfaces.  That seal can be described by taking two pieces of glass and pressing them together, they come right back apart.  But if you place some oil, or water on the glass surface, then pressing them together, they will lock together, sometimes requiring a great deal of force to dislodge them.  Cross hatching the surfaces helps to minimize this seal.  It is the same reasons that cylinder bores in your engine are honed.  As a side benefit, I have seen a great reduction in seal failures, lengthening their service life.  Each pair of forks and shocks serviced by us gets this treatment.

Stick around and the next installment on my blog will be to talk about the difference between high and low speed damping.  Just a hint; it has nothing to do with your speedometer reading……

Monday, October 19, 2009

Basic Suspension Setup

Today I would like to talk about setting the sag on your motorcycle. This is probably one of the most misunderstood, yet simple things to set up. First, you’re going to need a helper, a tape measure and a pad of paper to scribble on. You will also need to get your total suspension travel from your owner’s manual or some other reference material.

We need to take three measurements. R1; unloaded sag, R2; static sag, and R3; rider sag. What you do is measure from your axle straight up to some point fixed on your bike. See the photo. The first measurement, R1 is taken with the suspension fully extended. All weight is removed from the bike by either putting it on a center stand, work stand, or by pulling it over on the side stand while your friend measures.

Then measure for R2, which is the “Static Sag” is with the bike only carrying it’s own weight, off the stand, balanced upright. The third is R3, which is taken with you on the bike, at least a half of a tank of fuel, all your gear and what load you normally carry. I find that I can balance near a wall using my elbow to keep me right at that balance point while my friend measures.

Now that we have those numbers, you will need your total travel from your owners manual. I am going to use 10” of suspension travel as an example. Your bike should squat (R3) 30% of your total travel. In our example’s case, that should be 3”. If you squat more than 3”, you need more preload into your rear spring. If you squat less than 3”, remove some preload.

Ok, so where does R2, the static sag come in? Good question. You bike should squat from .5” to 1” depending on the bike you have under it’s own weight. If you have to put in so much preload on the spring to get your R3 number correct that you have less than .5” of static sag, your spring is too soft and you need a stiffer spring.

If your rider sag is correct, but you have more than an inch of static sag, your spring is too soft. And obviously, if you can not get your rider sag correct with your stock spring no matter how much preload you put in or take out, you need to go stiffer or softer with your spring.

Getting your spring settings correct can totally transform how your bike handles and should be done immediately after getting a new bike. It is one of the cheapest modifications you can do to your bike that gain the most in return.

In my next article I will talk about setting the sag in your forks.