Hey everyone, while getting my bike ready for tommorrows ride with dgyver, i took a look at the rear pre-load cause I think my bike feels "squirely" at above 60 mph indicated. What did I find? Well, the rear preload had been set to 1!!!
SO, I got out the clymer manual and it said that I had the necessary wrench in the tool bag! It was there, and I proceded with some difficulty to get it turned around to the number 4, which clymer states is factory stock. I had to use a piece of pvc pipe over the handle of the wrench to get enough torque to turn the pre-load while the bike was on the center stand with the rear wheel off the ground. Does that sound normal for the amount of torque required to adjust the preload? Or did I mangle something and just dont know it yet?
Also, I wanted to know what the general rule of thumb was in regards to pre-load on the rear shock? What will softening or stiffening the rear shock do to the overall handling of the bike? I only weigh 145 or so without gear, so probably 155 with gear.
Thanks for helping a noob out.
Andy
It is tough to turn the preload adjuster. And it gets harder as the preload gets stiffer. Try spraying some WD40 on it and get the preload maxed out to 7.
If you don't like it you can back it off easy enough on the ride.
It may be a firmer ride, but it will wallow around less and be more stable.
Most of the time you think it's the front end wobbling, but it's the rear causing it.
The general rule of thumb is that preload changes ride height, not stiffens the suspension.
Ideally, the fully extended suspension (on the centerstand) would sag 1-to-1 1/2 inches with the tire on the ground and you on the bike. If you have a less than ideal inseam you can back off the preload more to get closer to the ground.
By increasing the preload on a spring, it compresses it. Causing it to act like it has more weight on it. If you added the same force on the spring without changing the preload, the suspension will sag more. Adding preload, in essence pre-sags the suspension. So the ride height will lower less.
But it won't increase the ride height. The only way to increase ride height is to lengthen the shock or linkage. While preload doesn't change the spring rate it sure feels stiffer:mrgreen:
Bob,
As I stated, changing the preload changes the ride height. Of course, the adjuster doesn't change the maximum ride height or the minimum ride height or the ideal ride height.
If changes in preload make the suspension feel softer or firmer it's because changes in ride height shifts the weight bias front to rear and vice-versa.
Same deal for the forks.
I may be off here, but the amount of force that a spring pushes back with is proportional to the distance it is compressed. F=kx where F is the force, k is a constant and x is the distance compressed from fully relaxed. So if you "pre-compress" the spring, for example 1 inch, it will take more force to compress it that next inch than the first inch. This would make the suspension stiffer.
Another question about preload. Will riding on a higher level cause your shock to wear out quicker than say a lower level since there is always going to be more force on the oil regardless of how you ride?
Simon
QuoteSo if you "pre-compress" the spring, for example 1 inch, it will take more force to compress it that next inch than the first inch. This would make the suspension stiffer.
But the effect of
preload as you describe is overcome the moment we sit on the bike. The only time that preloading of the spring will be felt is when the suspension tops out as when the wheel catches some air then hits the ground. So preload might be an issue on a MX bike. On a street bike, allowing 1-to-1 1/2 inches of sag keeps it off the top of the suspension 99% (made up number) of the time.
Allowing only a 1/2 inch of sag would have the suspension topping out quite often which not only tends to catapult the rider off the seat but will transmit the harshness of overcoming the initial preload.
QuoteAnother question about preload. Will riding on a higher level cause your shock to wear out quicker than say a lower level since there is always going to be more force on the oil regardless of how you ride
Again, since preload doesn't affect the spring-rate the damping will be dealing with the same amount of force no matter how much you crank the adjuster up or down. Do shocks internals have progressive damping regarding the position of the stroke? Dunno. That might matter.
Hmmm...I think you're right. What i'm getting, then, is that when you are sitting on the bike, the suspension must be able to traverse both up and down for when you hit a bump or valley, respectively. Therefore, when sitting on the bike at rest, there should be enough room in the spring for both upwards and downwards motion. With my 200lb butt on the seat, i need to set preload higher than some 120 lb lightweight so that the spring compresses the same distance when i sit on the bike. This gives us both optimum upwards and downwards travelling ability. This is i think where that 1 - 1 1/2 sag that you are talking about comes into play. Unfortuneatly, the total travel of the suspension is less for me because of the preload...I guess i need to lose some weight.
And...if i set too much preload then the rear tire won't follow valleys or rebounds making for a harsher ride...however too little preload and it's easier to bottom out, again making for a harsh ride. Neat..
Quote from: Diderich...Unfortuneatly, the total travel of the suspension is less for me because of the preload...
Actually the purpose of setting the sag is that so riders of different weights will still have the same amount of travel.
Think of the rear spring as if were holding up an elevator in a ten story building. With 100lbs of weight the car rests at the 5th floor and with 200lbs it rests at the 4th floor. Increasing preload brings the 200lbs back up to the 5th floor so it starts out at the same place. Each can visit the 1st and 10th floors with equal force.
read SportRider's tech articles on suspension setup. Rebound is not automagically adjusted. Pretty much every OEM shock has abominable rebound damping and at the pricepoint of most sub-7000 bikes it really blows.
Adjusting spring preload is only the first step in suspension setup.
You set it so you have a certain amount of sag when sitting on the bike in full gear and in riding position, while the bike is held by other people.
It can be changed a bit to suit different riders. But it gives a base line to start with. Then you start working on damping adjustments. Of course the GS has NONE, so your stuck. Except for different weight fork oil.
Lets assume you have fully adjustable suspension. There are many things to consider. What type of bumps for instance. On a track it's a little easier to setup, because the street varys from smooth to cobblestone :lol:
Depending on how much preload and the spring rate, you adjust the compression damping to slow the travel when it hits a bump. When the tire passes the bump the rebound setting keeps it from unloading too fast and kicking up the bike.
Too much compression damping and the initial hit will be too harsh. And too much rebound damping and the tire could lose contact because it can't follow the contour of the bump. This can also cause "packing" where the suspension can't react quick enough to several bumps and starts packing down.
Not enough compression or rebound damping results in the tire bouncing and losing contact with the pavement. So there is a fine line where it follows the contour of the pavement while not upsetting the chassis.
My Penske (rear shock) has high speed and low speed compression damping (to complicate things). But it allows more adjustment once you figure out what the hell does what. I can set the low speed damping stiffer to allow less squat exiting corners, which helps the bike steer tighter. And the high speed softer to soak up bumps at high speed.
Rebound is set to allow the tires to return quick enough to stay on the ground, without being a pogo stick.