rear suspension setting

[Phil B]

On my way to work, there is a long undulating section of freeway.
small regular ripples or something in the roadway, for about a mile. no visible actual ridges, but they result in a bumpy feeling, about every .7 seconds.
(Or maybe it is section breaks, in the raised freeway? not sure)

Vaguely annoying in a car. REALLY annoying on my gs500.


I'm wondering if it is usually better to set the adjustable rear suspension more towards the 1, or the 6, for this sort of thing.

[lidskid]

I don't know but will be watching this thread   

[kininja]

Let's see if I get corrected, and this is just my theory, but I think it'll be more of a matter of personal preference.

Adjusting the preload on the shock helps if you're trying to setup the bike for a heavier or lighter load but won't really help much in this type of situation. A lower setting, towards 1, should soften things a bit but this is more of what you would need rebound and compression adjustment for. A lower setting will just make it more like bouncing on a matress as opposed to riding a hardtail, but it won't help eat up the bumps.

Again, anyone, please feel free to correct me.

[burning1]

Assuming you're not bottoming out your suspension, adjusting the pre-load won't have a significant impact on bumps. If the bump compresses the rear suspension an inch, it'll still compress the suspension an inch whether you use setting one, or setting six. Pre-load doesn't affect suspension stiffness, it simply affects where the suspension sits at rest, which controls how far the suspension can compress or rebound.

If you need proof... Have someone sit on the bike, and measure how far the spring compresses on setting one, or on setting six. You'll find that the spring is the same length, so long as you don't add so much pre-load that the suspension is completely topped out. What will change however, is how far the shock is extended, and how high the tail of the bike sits above the ground.

Suspension upgrades can help here; a better shock will have better valving which will tend to better absorb the bump. It will also provide some external rebound and compression adjustment that might help. You might also try playing with your tire pressure a little; the tire is an essential part of your suspension. Adding a little pressure will tend to stiffen it, and reducing the pressure a little will tend to soften it. Be aware that taking away a lot of pressure will increase tire wear, and can overheat the tire. Likewise, adding a lot of air will tend to cause cold tearing if pushed, and will tend to reduce traction.

[Phil B]

Assuming you're not bottoming out your suspension, adjusting the pre-load won't have a significant impact on bumps. If the bump compresses the rear suspension an inch, it'll still compress the suspension an inch whether you use setting one, or setting six. Pre-load doesn't affect suspension stiffness, it simply affects where the suspension sits at rest, which controls how far the suspension can compress or rebound.

Err... you make it sound like that 1-6 adjustor thingie on the rear suspension, is not much more than a height adjustor :-/
What am I missing here?

[burning1]

It's not just a height adjuster. Here's a practical example of how pre-load can affect the suspension, to help understand it...

The rear suspension of the GS500 has 115mm of travel. Without your weight on the bike, it sits near or at the top of of travel. With pre-load on the most relaxed setting, a 200lb rider might compress the suspension by 50mm or more... That means, that only 65mm of compression travel is available when he hits a bump. If you hit a bump that requires 80mm of travel to absorb, the suspension bottoms out, becomes more or less solid, the bump is transferred through the bike, and the rear tire is likely to be thrown off the ground causing major traction problems.

So, we add some preload... Now, the rear suspension is only compressed by 35mm when the same rider sits on it. That 80mm bump is absorbed (just) and everyone is happy. Generally, if you find yourself bottoming out the shock a lot, it's good to add a little preload.

It's good for the suspension to have some travel available for rebound too, which is why we don't just crank preload all the way to the tightest setting.

Keep in mind, this is different from a straight ride height adjustment. With a ride height adjustment, you're changing how high the tail of the bike sits, without changing where the shock is in it's range of travel. So, if you have 35mm of preload, and were able to raise the ride height by 25mm, you'd still have 35mm of preload, and it would still take 80mm of travel to bottom out the shock. A common way to change the ride height of the GS500 is to install lowering or raising links. On some other bikes, ride height is built into the shock, or can be changed by shimming one of the mounts (E.g. the R6 shock, when installed on an R6 (doesn't work when installed on the GS.))

Keep in mind that suspension components and tuning parameters interact in incredibly complex ways. Adding preload will permit the spring to compress further before it reaches the end of travel, which means that there is actually a little more resistance at the end of stroke before the suspension bottoms out. It also tends to point the nose of the bike downward, which takes a little weight off the rear tire. It also tends to decrease the pressure on the gas in the shock, which acts as a progressive secondary spring, leading to a slightly softer spring rate.

Another issue with pre-load is that it's possible to add so much that the spring doesn't compress at all when we sit on the bike. If we do this, it means that any bump will have to transmit some force through the bike to overcome the initial pre-load. This will make the suspension feel very non-compliant.

Suspension is very complex stuff, and I'm pretty novice at it in a lot of ways.