Lets delve deeper into setting up the suspension on your bike
Setting up your motorcycle is simply adjusting the movable parts necessary for the rider to obtain the maximum control and most effective riding. We have to remember that no matter what type of bike you have, all motorcycles are handed with a neutral setup from the factory. This neutral setup makes for an easy maneuverability and a generally predictable handling on the limit, but a personal setup can always optimize the bike to your liking. No rider is alike and everyone has their own different riding style.
What kind of signs from your bike could you get if your setup is not well done? You can experience that the bike is hard to turn, it wants to steer one way when you accelerate, or simply doesn’t respond to the inputs as you would expect it to. When this happens, it is the time to go back to the drawing board and try to fine what element is out of balance.
Before doing anything to the neutral bike setup, you must be clear on certain things. It is important to find a balance in all the movable parts, find a way that every element complements each other and work together according to your liking. That is the complicated part, finding an equilibrium in the setup. There are 3 important areas to have in mind: geometry, suspension and tires.
In the second post from this “Motorcycle Setup” series, we will focus on motorcycle’s suspension. Check our first post about motorcycle geometry.
Suspensions are in charge of absorbing the bumps of the road to maintain constant contact with it. The suspension is also in charge of supporting the weight transfers of the bike. This means that a good suspension setup will allow the bike to turn correctly when necessary and accelerate efficiently. Suspensions can often be more complicated than motorcycle geometry since suspensions have more moving parts and aspects.
The variable elements on a suspension can include: preload springs, preload force, hydraulic compression (regulates the compression speed) and extension (regulates the speed of return) and oil. More affordable and simpler bikes may have fewer variables such as only springs to reach the desired setup. In very simple suspensions, there is not a whole amount of room for improvement as there are not enough variable elements to do so. In these cases, to know if the preload force of the spring is the right one, we have to calculate the sag.
Sag is the amount of suspension travel used up when the bike settles with a rider on board. To alter the sag you need to adjust how much the springs in the forks and the spring in the rear shock are compressed (also called altering the springs’ tension or altering the pre-load). It’s very important to calculate this, because if this is incorrect, the bike’s balance in an abrupt turn will be atrocious.
There are 2 types of sag calculations: sag with rider (loaded sag) and sag without rider (free sag)
In a factory bike, free sag comes already calibrated. But when doing the loaded sag you might as well do the free sag, just to be sure. To do a free sag calculation you might need another person to help you out. The bike must be suspended form the ground, but just touching it. It shouldn’t have any kind of pressure for an accurate calculation. The process is simple, you want the suspension to extend to its maximum and at this moment you will measure the suspension travel.
After this you will let the bike stand by itself and measure again. On upside-down forks front suspension, measure the distance between the fork seal and the point where the slider joins the lower casting (the mount for the wheel spindle and brake caliper). On conventional right-way-up forks measure from the fork seal to the underside of the lower fork yoke instead. After taking measurements on the suspension under its own weight and the performing the free sag, you can subtract the free sag numbers to the regular suspension numbers.
To calculate the loaded sag, the same process needs to be done, but with the rider on the bike. The suspension travel should be measured from the shock’s fixed point of the sub-chassis to the center of the rear wheel axle. Correct values will depend on the route of the suspension, but normally the correct sag is usually in 1/3 of the route or in 25 or 30%.
You can consult the measurements with the suspension manufacturer specs. Once you have calculated the sag, you will notice if the springs needs to be changed or just be adjusted. If the sag is less than the correct percentage, you may have to substitute the spring for a softer one. The opposite will happen if the sag is more than the correct percentage, a stiffer spring may be needed. In and adjustable spring rate suspensions, you need to increase the fork tension/pre-load by turning both pre-load adjusters in/clockwise if too much sag.
Now have a better understanding of suspension variable elements in your bike and how to sag.
Until next week!
Photo Credits: Motorcycle News