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 Post subject: Suspension progress on my new car
PostPosted: Mon Apr 27, 2009 9:21 pm 
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Well my GT has pretty much all the same stuff as my old car, and since I've taken lots of pictures I thought maybe I should post it here:

Once again I have a set of STi suspension, and here's a picture of the ride height:

Image

You can see it lowers the car a little bit. The top and bottom mounting for almost all 02-07 impreza suspension is the same as that of 95-99 Legacies (seeing how they're both 2nd gen subarus), so you can just take the whole setup and bolt it right up. The exception to that is 05-07 STi parts, because those cars have bigger front uprights, hubs, and wheel bearings. For a 1st gen, the rear strut top bolt pattern is different. You can use 90-91 legacy awd rear tops or file out the bolt holes in the chassis.

The other thing to note is that impreza sedans have a wider track. that means less negative camber, and that's a very, very, very bad thing if you are looking for a handling improvement. The car and the tire lean over in a corner, so without negative camber your tire is riding on the outside edge. The sidewall and part of the tread have significantly less traction that the entire tread, so making sure there's enough camber and not too much roll is critical for increasing grip. I recommend starting at -2 degrees on the front wheels and going up from there for track and auto-x usage (or anything else with frequent hard cornering). If the toe is zeroed out and the rest of the suspension/steering is in good condition, -2 degrees adds practically no tire wear, even with mostly street driving.

Even on stock struts that fit the car properly -2 degrees isn't possible, so that means you need some camber plates, an extra set of bolts, or to slot the struts. Camber plates are expensive (but do have some very nice additional benefits). Camber bolts are smaller and do not create as much of a clamping load as oem bolts. Back when I had 04 sti suspension on my 93 legacy I put my front struts in the endmill at work and milled them out for a stock camber bolt in the lower hole:

Image

It was a neat idea, but necessitated drilling out the hole in the upright with a drill bit that was hard to track down. To top it off, I only ended up with about -1.3 degrees of camber, which a bit less than i was expecting.

With the new car, the first thing I did was buy some fresh sti take-offs because my old suspension was pretty worn out and abused. They came out of an 05-07 sti, had low miles, and cost me $140. All I had to do to make them fit was swap the front housings over from my 04 struts:

Image Image

Image Image

While I was at it I cleaned out and re-greased the housings, slotted out the front lower holes, and cut down the front bumpstops. I slotted out the holes because I didn't have the money to spend on camber plates, and I didn't use aftermarket bolts because I had already enlarged the lower holes so they wouldn't work right. It also meant I would keep the stock clamping force. I do have aftermarket bolts in the rear and haven't had any problems in 4 years. They are set to the max negative position which almost eliminates the possibility of slippage. The bumpstops were cut to soften up the front slightly. Stock, an sti is almost right on the front stops. Trimming them really smoothed out the ride and reduced the notorious bobble head. It also decreases the front spring rate slightly relative to the rear which should help make the car a bit more neutral.

Well, those are the struts and springs I have on the car. For the price, I really like them. They aren't too harsh, have enough spring to keep the car relatively flat and composed, and the dampers, while a little rough, work pretty well over everything. Given a little more money I would go with koni inserts, and after that a good coilover like AST or KW. I don't have a very friendly opinion on most of the less expensive coilovers out there.

To compliment the sti parts, I have some other stuff. One of my favorite mods is the Whiteline ALK. Anti-lift kit tends to be misinterpreted as something that reduces lift. In fact, it removes the anti-lift and -dive geometry of the front suspension and will increase the lift and dive. The reason for this is to transfer forces through the strut and spring instead of the chassis. What this does is soften up the front under braking and acceleration, which will improve grip. That means less understeer on corner exit, and more front grip on corner entry. Here's the ALK:

Image Image

Image Image

You can see that it replaces the rear control arm bushing with stiff urethane, and that the mouting point is changed. That mounting point is moved down, to remove the anti geometry in the front suspension, and outward to increase static caster. The stiffer bushing reduces dynamic caster loss, and I also noticed that it really solidified the feel of the front end, especially under hard braking.

If you were wondering about getting one of these, well, you should. I recommend the sport version. It does add a bit of noise, but I completely forgot about it after a day or two. The race version is apparently really loud.

The suspension, alignment, and ALK alone made a huge difference in the feel of the car. Suddenly it went from being floaty and vague with sort of a sporting feel to solid and responsive and incredibly more fun to drive. But, there were (and still are) a few little things that I wanted to improve upon. Installing the ALK makes the front of the car solid and quick to respond, but there's still vagueness in the rear. So the front sets in and the rear is still working on it, which leads to a little bit of a delay before the car feels right in a corner. To partially remedy this I put in some Kartboy subframe lock bolts and outrigger bushings. It adds a bit of diff noise, but helps a lot with the rear end. I'll eventually replace the trailing arm and lateral link bushings with group n rubber. Whiteline steering rack bushings went in there at some point as well. That's a really cheap and easy mod I can't recommend enough. All of that vagueness in your steering will disappear.

One thing I did right off the bat was replace the 16mm rear swaybar with an 18mm bar, and installed a set of kartboy endlinks. This also helped reduce front end push, and the added roll stiffness and stiffer endlinks/bushings made another increase in responsiveness. It still was a little pushy and rolled a bit more than I liked, so I got some bigger swaybars:

Image Image

Plus 04+ impreza mounting brackets to go with the rear bar.

Image Image

Those are whiteline 22mm adjustable swaybars. I started by just installing the rear bar set to soft. The first impression was "holy crap! this is amazing," since I finally had a Subaru that didn't really understeer. The 18mm rear bar, and alk, alignment, and stiffer suspension all contributed toward more neutral cornering, but it was still a front heavy, awd car, and so it understeered. A lot less than before I did anything, but still that push was there, especially at the end of my favorite onramp. The first time I went down it with the bigger rear bar, I came out of it going way faster and wasn't pushing out toward the guardrail.

The front bar caused a nice decrease in body roll, but it didn't cause a dramatic change in handling like the bigger rear bar. Right now I have the front set to soft and the rear to medium, and the car handles well. I suppose I'll play around a bit more with the settings, but I need to get in an environment where I can actually drive the car a bit.I suppose I'll get out on an auto-x course or track, or just go up to malibu or something one of these days. I also need some sticker tires.

In conclusion, I love driving my car thanks to all of this suspension stuff.

Suspension plans for the immediate future:

RCE black or yellow springs
whiteline RCA
whiteline offset top mounts
probably some stiffer bushings
better tires

Current alignment settings:

front camber: -2.5 degrees
rear camber: -1.2
no toe.


Last edited by jamal on Sat Mar 13, 2010 9:49 pm, edited 4 times in total.

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PostPosted: Mon Apr 27, 2009 10:42 pm 
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Location: Utah
Great writeup, per usual. I'm very interested in this because of my recent acquisition, of course.

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 Post subject: Re: Suspension progress on my new car
PostPosted: Thu Jul 28, 2016 10:15 am 
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Joined: Fri Mar 25, 2016 2:48 pm
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Location: Beautiful Downtown Goode, VA
Good work Jamal, what spring rates do you recommend for a 91 legacy wagon on Ksport coilovers, they came with 425 front, 285 rear. I havent installed them yet so I have no idea what I can expect. This is for a performance oriented street car that will only occasionally be tracked or autocrossed.


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 Post subject: Re: Suspension progress on my new car
PostPosted: Thu Jul 28, 2016 4:08 pm 
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Oh hey, here's an old one. I guess I could track down and update the pictures. I had an issue and had to re-install gallery so now there are a lot of broken links out there. Although I might just be able to change a folder name, they might still be in there somewhere.

There are some things in the text I would change a bit, and since then I did get some RCE black springs, whiteline top mounts, an RCA, and TiC bushings for the rear end. I'm due for some new struts at least and would not recommend using GD sedan stuff anymore because they are old now and the parts for a wider track can cause a bit of binding.


Anyhow, 425/285 is too much of a split from front to rear. For a car with f/r struts (newer subarus have a multi-link) You want to keep the fronts about 15% stiffer than the rear or even less depending on the situation. That's the same as the stock sti at 224/195. I think the RCE springs I have are an even smaller difference, something like 285/270, and I have even gone so far as to use stiffer rear springs on a few cars.

425kg springs are 50% stiffer than 285, and it's on a wagon which tends to have a heavier rear end. So those spring rates are way out of balance. I would want the rears to be closer to 400lb. I don't think you'll be able to soften the front due to travel issues. It will make the ride worse. Rear spring rate has a big effect on comfort, and that is part of why so many coilovers have very soft springs. The dampers aren't great, the springs are fairly stiff, and they don't have much travel, so I'd guess it's done mostly for more favorable reviews.


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