Shock Rebound Stiffness

[offroadrabbit]

What are people running for rebound stiffness?
Just picked up some KONI specials, to use with some progressive rally springs.
Obviously the softer it is, the faster it rebounds, so what's good for a FWD rally car?

[DrewP]

I don't think anyone who is seriously rallying uses the stock valving anyway, both Koni and Bilstein will re-valve the shocks to make them appropriate for use with rally springs and whatever your new curb weight is (assuming it doesn't weigh the same as stock).

I'm a little curious about this too.

I did a few rallycrosses in my '85 and it has Koni sports set to 'medium' on all 4 corners, and B&G lowering springs. With the open diff and too much power it was hard to tell whether I needed more or less spring or damping. I also had both ARB's installed too.

I think one of the big things you want to dial the dampers in for is to keep things from bouncing and picking up wheels too much over uneven surfaces. Not really something that happens on a (relatively) smooth rallycross course.

[Sam]

Have any of you guys run with extra tall springs for baja, etc? I discovered a pretty nice beach access near me the other day that looked like it might be ridiculously fun.

[Geoff]

Sometimes Bilstein puts a sticker with the valving they used on revalved shocks. I have a few different sets, most of which don't have stickers but as I remember the fronts were 300,100 (compression, rebound) and the rears were 400,125.

Of course there are no units so unless you know what units they're stating the numbers are useless. I seem to remember once seeing shock valving expressed in pounds per inch per second. In other words, it takes 300lb to compress the front shock at a rate of 1 inch/second. But I'm not sure those units (or compression rate) are correct.

Other factors are whether the shock is valved linearly, progressive (gets exponentially stiffer when the shaft speed increases) or digressive (gets exponentially softer when the shaft speed increases). Typically these basic shocks are linear.

[Geoff]

Sambone,
Seth put some super tall springs on his 2dr 900. I think he got them from Rock Auto. The rears were 900 overload coils and the fronts were from some American beast (Chrysler?). He ended up having to cut them down a bit and it was still tall. We used it for reccee at NEFR and we didn't bottom out once. It sat taller than the RallyHo 900 rally car.

[offroadrabbit]

Because mine aren't re-valved I think I'll go with full soft.. One of the front shocks was defective so I will only be able to put the rear in before my RallyX this Saturday, but once I get the fronts in I'll see what it's like and if I desperately need to re-valve them for more compression/less rebound.

[SaabsBreakDown]

isn't moar rebound moar better?

I have bilsteins HD's (stock) on the rear and DelCarbone "rally shocks" (vanlandingham's words) on the front. I have a set of 3 stock bilstein fronts waiting to go on that i've been meaning to send to get re-valved for years. 900 turbo rear springs, and stock 99 (non-ems) springs on the front (i have turbo springs for front but haven't installed).

So 300/100 for front? does anyone have a 1-800 number? :)

[offroadrabbit]

Well after installing, testing, re-researching, I've found it depends on way to many other variables to make a conclusive statement. But if you have soft springs, you need more compression to prevent bottoming out, and less rebound because the springs aren't as strong to resist. Alternatively you can run progressive springs like I have done, so you get softness to start, but as it compresses more with bumps spring rate increases so you don't bottom out. This means you can run more OEM style shocks with less compression, still have a smooth ride, and don't need a ton of rebound (still more than OEM) because it softens back out as the spring returns. With my adjustable Konis, I'm running 50% stiffer in the rear, and 100% stiffer in the front (these front springs are too stiff so I will probably be running more like 50% with proper springs). I really like the feel of this setup, and while it's smooth there isn't much squating at all, so weight transfer is fantastic.