This can get a bit long winded so I'm going to break it down into sections. Sure, I'd like to sit here and type it all in one go, but I just don't have that huge of a chunk of time, and the second section of this is going to require some pics and drawings or nobody will get what I'm talking about. That, and I really want to try and get the brakes changed on the SVX today.
So, to start things off we'll talk about travel and lowering your 2008. We'll keep this confined to the rear of the car as the front hasn't changed much from the older models.
We'll start with this with some measurements.
At stock ride height you're sitting at 14.625" from hub center to fender lip.
At full bump you're sitting at 12.0"
At full droop you're sitting at 18.75"
These measurements were taken first with the car on the ground, and unloaded to get the stock height.
We then removed the spring so we could jack the wheel through it's full motion.
This means that:
Bump travel at the wheel 2.625"
Droop travel at the wheel 4.125"
Truth is, the bump travel sucks, and the droop travel is just ok. As an aside, the spring does not coilbind, and actually has a good bit of room for more bump travel.
Another thing that we noticed was the rear bump stop. It's rather long. It's also just about touching the top of the strut top at stock ride height. This means that any action you have back there in the way of bump actually starts to engage the bumper.
Since a bumper is basically a progressive spring this means that you are adding to the spring rate in the rear in a progressive manner. Go more into the bump stop, and you get a higher rate.
While ok for ride, this is not so good for handling. When it comes to handling progressive springs are hard to predict when entering a turn. This is why good aftermarket performance springs only have a small amount of progression and is pretty close to nill at stock ride height. Notice I said good springs.
So, lets say you want to lower the car. Well, here's the problem.
1) You don't have much bump travel to begin with, and you'll only make it worse.
2) You'll be deeper into the bump stops to begin with. Sure you have stiffer springs, but now you've made them stiffer still with the engagement of the bumper.
3) Rear toe and bump steer gets awful (more on this on the second part of the paper)
Now, how can we correct this? There's a few ways we can START to address the problem.
1) if you are using the stock rear dampers do not lower the car with just springs. Even if they are stiffer springs we have found that the car will suddenly overcome the rear grip and unpredictably step out on you. Not a good thing.
2) You can cut the rear bump stops or get new shorter ones. We've actually suggested this a few times to folks now. The idea is to let the car move in bump a little more before engaging the bumper and hope that the event (the corner or bump) is over before you get too deep into the bumper.
3) There a cage on the top of the stock strut. You can cut that off, and it'll give you a little bit (like .25") of bump travel. Here's the deal with that cage - it creates air space and an exit path so when the bumper hits the top of the damper it doesn't shove air into the top seal. A good example is the party trick of a beer bottle. The one where you fill the bottle complete with water all the way up the mouth. You then slap the palm of your hand down on the top, and the bottom of the bottle breaks out in a perfect circle. Cool for a party. Bad for your dampers. So, if you cut that cage off you'll need something to let the air out from between the bumper and the strut top. This is known as an aerator disk. It's simply a washer (usually plastic of some type) with a slot cut in it so it looks a little like pacman. This gives the air a space to get out instead of through the upper seal. Despite this I do NOT recommend cutting the cage off.
4) You can get a new damper. One with a shorter body, and a decent amount of travel. Sure you could get a cheap damper with 3/4" of travel, but that's really not the point is it?
We'll work with stock numbers here so no lowering taken into account. We've got 6.75" of travel back there to play with given the stock damper. All other things being equal we would like to see that even out a bit for bump and rebound. You can't do a straight up 50/50 split. The reason being that when you're in a turn you've got plenty of grip on the bump side, but if you're fully compressed on the loaded side you can pretty much anticipate that you'll be fully decompressed on the unloaded side. Now, add tire flex into there and you're beyond an already barely touching tire on the unloaded side.
As we know from inside rear tire lift on the old cars a tire in the air means no go. Even with all the diffs you just don't have enough locking factor in the diffs to account for a tire in the air. That means you have to wait for the tire to settle back onto the ground before you get on it. Not good.
So what we need is a damper that sets us up with a little bit of an uneven split. While I have not figured out exact numbers something like a 45/55 or 48/52 bump/rebound split would work nicely I believe. So you're looking at 3.0375-3.24" of bump travel if you look at those numbers. Keep in mind this will also depend on the tires although if you're on flexy all seasons or winters I'm going to hope that you're not going all out.
Given this what can we do? Well, if we're talking the same overall length of body and shaft at rest we need a strut that's going to have a shorter body than stock, and be very efficient in travel. At this time I am not aware of any that fall into the category.
There's another thing we can do, but I need to do some research on it as it will require a part, and I don't want to give it all away just yet. At least let me be first to market on some things.
On the subject of coilovers - the answer is MAYBE. I know the numbers for the AST. I do not know them for the KW, Ohlins, Cusco, BC or any others that are now offered for the 08. If folks have that info I would appreciate it.
So, in conclusion here's what we have:- Rear bump travel sucks
- Lowering with just springs at this point in time is NOT the way to go for handling. Unless all you want is looks. If it comes to that I can't help you. Not being a jerk, just being honest. We're function over form shop, so we don't worry about how cool stuff looks.
- Cut or replace stock bumpers
- Find a better damper or go to good coilovers (hard to do at this point in time, but it's being worked by us and RCE).
Next up on the agenda:- Rear toe control and rear bump steer
- Rear camber and its control.
2008 Rear Suspension Part I: Travel 
