Rear suspension questions...

[DOG ON]

Ok guys, I need your advice...

I have a class 4 car appears to be very soft on its rear suspension, I have a 2.5 King shock on each rear wheel with a 300 / 400 coil setup, the car weights exactly 2,200 lbs total..... it is distributed like this:

770# on each rear wheel (1,540# rear) and 660# on the front all together. The car feels soft an its rear end bangs everywhere, just look:



Are the rear coils too soft for the weight? What is the rule of thumb when you calculate spring rate with a shock? Can the valving be also to blame here? what valving should I ask for?

Thanks

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[shock pros]

That does look soft. Ok let's start at the beggining...
1. How low do you have the rear sitting? With a single coil-over you want to have the suspension sitting somewhere in the ballpark of 70-75% open. Example: 12" shock will have around 9" shaft exposed. What length shock do you have and how much shaft is showing at ride height?
2. How much preload is there on the coils to get your current ride height? This is to see how close we are on the spring rate. Preload is different than threads exposed. Preload is actual tightening of coil from hand tight on the preload ring
3. Do you know what valving you have in the shocks to begin with?

Let's start here and I'm sure we can help you

[DOG ON]

That does look soft. Ok let's start at the beggining...
1. How low do you have the rear sitting? With a single coil-over you want to have the suspension sitting somewhere in the ballpark of 70-75% open. Example: 12" shock will have around 9" shaft exposed. What length shock do you have and how much shaft is showing at ride height?
2. How much preload is there on the coils to get your current ride height? This is to see how close we are on the spring rate. Preload is different than threads exposed. Preload is actual tightening of coil from hand tight on the preload ring
3. Do you know what valving you have in the shocks to begin with?

Let's start here and I'm sure we can help you

Answers:

1) I went for 60%, my shocks are 14" Kings 2.5

2) On the preload, I set it uo to be 60% of the travel down at ride height.

3) I just asked to be "medium" for compression and "medium" for tension as I didnt know where to start before the ecotec set up

Thanks for your help!!!!

[shock pros]

ok here's what I need youto do for the pre-load. I need you to jack up the car till the rear suspension is hanging at full droop. Measure how far down the coil pre-load ring is located before you start.
Once the car is up loosen the pre-load ring till the coils are just barely loose. Then measure how far you had to loosen back the ring to get there. This is going to give us your real pre-load number. I need to know this to find out how close you are on the spring rate. Try this first and let me know.

Example: You had 4-1/2" inches of threads showing and you loosened up the ring till the coils were barely loose. THen you had 2-1/2" of threads showing. That means you have 2" of preload on the coils.
More than 3"-4" of preload and we're probably under sprung
Less than 1/2" of preload and we're probably over sprung
We should be in the 1" -3" range for your car.

Then we'll look at valving

[DOG ON]

OK, its 3.5 to 4 inches.....maybe I am a bit undersprung....

[cosmo]

Look's like a lot of leverage on the rear also.

[shock pros]

OK, its 3.5 to 4 inches.....maybe I am a bit undersprung....

It sounds like you might be. Like Cosmo noticed too, it looks like the rear has a bunch of leverage on the shocks, so we need to go up on the spring rate a bit. Right now you're at about 171 lbs of main spring rate and I think you might need low 200s. Maybe try getting another coil in the 400 or 450 range and see how you feel the back end respond to that. Keep us posted

[PhillipM]

Just from the video, it looks quite undersprung, I'd say you need at least 25% on the rear rate, maybe more - it also wants some low speed rebound dialling into the dampers.