(Disclaimer: this isn't done yet. I figured the best way to get it done was to put it out here for comments. There are probably sucky parts. I will fix them
(Disclaimer2: this does not discuss shocks/struts or coilovers in much detail.
Those will be done in separate FAQ's.)
Two quick rules to remember before buying lowering springs:
1) Most lowering springs suck.
2) If it looks sweet, it's probably too low.
Here in the suspension tech forum, by far the most popular question is:
"What springs should I buy?"
While no static document can give you a definitive answer, we can definitely help you go in the right direction and ask the right questions. This document is intended to do just that.
What springs should I buy?
Jumping the gun a bit, eh? Here is some background reading:
-Suspension/Brake forum rules: read this before posting
No, seriously, read that first. If you post a spring thread and you haven't read it, we'll know
- How car suspensions work, including a definition of Macpherson Struts:
- High performance handling handbook - Don Alexander - if you are after something that is technical, yet pretty readable, this is pretty good:
And finally, and perhaps most importantly:
- Canonshooter's guide: "Lowering your Impreza?" - lots of specific firsthand experience in here as well as good technical background.
Why would I ever want to swap out my factory springs in the first place?
There are many reasons.
1. Aesthetics. Most cars look better with less wheel gap.
2. Handling. Lower/stiffer springs can reduce body roll and change the car's handling balance.
3. Ground clearance. Taller springs (say if you have a WRX and you go off road a LOT) can help on rough terrain.
4. Ride quality. In some cars, aftermarket springs may actually ride better than the factory springs.
Most people's reasons involve some combination of #1 and #2.
Why would I bother with just getting springs when I can buy coilovers? Sport Compact Car convinced me that if I don't have coilovers, my car will never handle well, I will never get any dates and my dog will die from brain cancer.
This is crap. If anyone tells you this, you should slap them silly.
A "full coilover kit" typically includes camber plates or at least some sort of hardened strut top, a coilover spring, a shock, and a strut body with height adjustment. While coilovers are a convenient way to get everything you need, they are NOT the only way and definitely NOT the only good way.
You can get all those things separately. A well thought out strut/spring combination can absolutely 100% hang with a coilover kit.
What should I look for in a good lowering spring?
1) Something that's designed for your goals! This means:
-designed for your car (sedan vs wagon; see wagon-specific information below),
-compatible with your shocks (stock or aftermarket)
-appropriate for your application (street vs track/autox) in both spring rate and height.
2) You are reasonably happy with how it looks. Not too happy though, because then it's probably too low.
What should I look to avoid in a lowering spring?
1) They should not be Tein S-techs.
2) They should not be "too low". As a general rule, if it looks sweet - it's probably too low. Going too low (especially combined with not going sufficiently stiff) means that you won't have much shock travel, which will make you ride on the bump stops a lot. This will have negative impacts on both handling and ride quality.
3) They should not be too stiff for your struts. Stock WRX struts generally start having problems somewhere around 250 lb/in. Stock STi struts can go a little higher, maybe 325 lb/in or so. Most aftermarket struts can go to around 400 lb/in or higher depending on valving and intended use. (NOTE: this is a section where I could use help!)
So... how low is too low?
This is a point of some debate. It also varies by car. While no Impreza likes to be lowered, the STi's situation is a little different than the rest of the Imprezas (see post #2 for details).
BigSky again with an explanation of how lowering a MacPherson strut car hurts the handling:
And I'll say it again - read the Canonshooter thread listed above.
I have opinions about which springs (other than the S-techs) are too low but I don't want to slam specific companies/specific products in here. Just research it and evaluate the reviews critically.
New information about the 08/09 cars:
Short version: lowering the 08-09 cars with springs only is a bad idea with the products on the market today. This is not to say that lowering it with bad coilovers is much better
It seems like you guys are really conservative. C'mon pops, kids lower their cars. Deal with it!
MacPherson struts suck. They have a really low threshold for sucking more with bad lowering springs. And there are lots of bad lowering springs out there. That's pretty much why.
What's a bump stop?
The micro-cellular progressive jounce bumper, or simply put, the foamy bumpstop, is actually a supplemental spring. It works to make the suspension progressive, allowing a smooth transition to full compression. What most people don't realize is that the foamy bumpstop is an active part of the suspension. Let's say you're sitting in your M3, 996, Accord, Golf, S4, or Civic. (Hmm I can't decide). They all use the foamy. Ok, you're in your brand new Integra, just drove it off the showroom floor and are sitting at the stoplight waiting for the green. The foamy is actively engaged even while waiting at the stoplight.
Car manufacturers use this brilliant piece of high-tech engineering for many reasons. By using an almost zero-weight supplemental spring, you can build the main (steel) spring with a reduced spring rate for a comfy ride.
BigSkyWRX has a REALLY good writeup here:
In short - once you lower the car, you are likely putting it in a position where you're more likely to be on the bumpstops. A common thing people do with lowering springs is to trim a nub or two off the bottom of the bumpstop. It's a tradeoff: you're less likely to hit it, but it will be harder (and less progressive) when it happens.
How can I tell when I'm hitting the bump stops?
Riding the bump stops and bottoming out are not the same thing.
What's the difference between linear and progressive springs?
Originally Posted by DrBiggly
Do note that the term "bumpstop" is somewhat misleading as there is never any real "bump" involved when one is making contact with them.
Here's a good writeup from Swift that silverF4turbo found:
I'm putting lowering springs on my car. I've decided! Do I need to do anything to my bumpstops?
8. What is the difference in progressive and linear springs?
Well linear spring theoretically keep the same spring rate regardless of stroke.
If you have a 6kg/mm linear spring, if you compress it 10mm it should only take an additional 6kg to compress another mm. Therefore, if you compress a linear 6kg/mm spring with 60kgs of force, it will compress 10mm.
Progressive springs are springs that gradually increase spring rate as the spring compresses. So, if the spring starts out with a 6kg/mm spring rate after 50mm of compression it may then measure 17.75kg/mm.
Using the above example a 6kg/mm linear spring will take 300kg to compress 50mm while it will take 594kg to compress the progressive spring.
For the WRX, maybe. Check out these threads:
Some lowering springs may come with instructions that say to cut them however.
For the STi, check these threads:
Do I need a camber kit when I lower my car?
If you lower your car too much, you may want to look into getting camber bolts or camber plates if you end up with excessive negative camber. What's excessive negative camber? That will be covered in an upcoming alignment FAQ. But for most folks, you probably don't want more than -2 or so. (massive generalization)
Do I need an alignment when I lower my car?
Yes! Your new, lower springs will affect the car's camber and toe, if you were to stick with exactly the same settings. Plus, the installation process involves removing your eccentric bolts and you're probably not going to put them back exactly where they left. You can mark them with paint to get them approximately where they used to be, but you still are going to want an alignment afterwards.
(shock FAQ): How can I tell how much shock travel I have?