Thread: affect of shock damper settings on corrugated roads

I've found the firmer setting (3) on sand dunes is much better than soft (1).

Haven't really tested corrugations. I just leave them at setting 3.

And switching between 1 and 3 is easy as I just go two clicks (either direction)

Originally Posted by prelude

As a follow up to my tyre pressure experience post in the general chat area, a question about adjustable shocks.

I currently run a set of terrafirma 2" adjustables on my P38. I have them set to setting 3 almost permanently. I always told myself I would set them to 4 on the road and lower offroad but it seems that this is the wrong way around. I reckoned a stiffer setting on bitumen would aid handling, certainly combined with the highway setting of the air suspension but I have now been hearing arguments that a softer setting on the bitumen would be better for a less harsh ride and a harder setting offroad to aid in less body roll through undulating terrain. (The logic seems to be that offroad is a slower speed so you need stiffer shocks and on bitumen the faster hitting bumps would need a softer setting...) Curious as to thoughts, experiences etc on this one?

In any case, whilst I was contemplating the tyre pressure settings and posting a thread about on the forum it occurred to me that shock settings also have an influence. As the corrugations gave way to potholes (badly worn roads) I found that increasing speed would solve that problem, as long as the holes were not wheel sized, but I also found that I went close to speeds that could become unsafe at some point. As I pondered along I came to the conclusion that the damper setting on the shocks resist travel in a direction basicly slowing the travel down. What one does when speeding up over corrugations is trying to find the point at which the air time of the tyre is such that you "slide" over the tops of the bumps. If I could make the wheel/axle go down less fast ie. stay up in the air a bit longer, I could slow down but on the other hand, the bumps that you do hit would translate into much harsher vibrations in the car.

Finally, since adjusting the shockies is not easy on this car I did not fiddle with them and I do not even know if they adjust bound and rebound equally but I was wondering if anyone has experience with this and/or knows more about this?

Cheers,
-P

Shock valving isn't really standard, there are all sorts of dyno curves but I suspect most are linear for both bump and rebound.

They have 2 rates, one for bump and the other for rebound. That rate is for a given shock speed and a bit like power and torque numbers doesn't tell you all of the story but it gives you an idea of what the shock is like.

Within the range of shock valvings options that you have on the shock, I think you will find they are not at all over the top with regards to being too stiff to perform.

As a rule of thumb, you will more than likely increase the shock rate and get better handling or decrease the shock rate and get a better ride if the changes in the shock valving affect both bump and rebound - some shocks change both bump and rebound, others only change rebound. The increased shock rate will give better control of the suspension and keep it in better contact with the ground, where low shock rates will be comfy but all bets are off when you hit rough roads and corrugations for vehicle control. It will also control body bounce and often bad shocks result in car sickness.

You will find that the comfort comes mainly from the changes in the bump valving and the bump valving is usually very soft compared to rebound because its the valving you feel through ride stiffness. Actually, I would bet money that most people who change suspension out because their springs are too stiff riding actually have a shock problem, not a spring problem.

Another point in relation to your comments, the shocks don't control body sway - at best they will control how quickly it takes a set, but it doesn't control it and I doubt you will feel a notable difference short of being on a race track.

My opinion is that when offroad, particularly on fast dirt and corrugations then you need a good shock with a lot of control if you want the vehicle to handle and to be predicatable.