In search of high-speed stability

[blklgt05]

I haven't read the entire thread, but over inflating the tires can be a pretty big cause to the car wandering at high speed. To get the best pressure and balance, you have to consider your avg mph/daily speed. For example... on the gas door of the CLK, you will see F28/R30psi 0-100mph speeds, and F30/R35psi 100+ speeds.

 

Parts that helps,

-bilstein HD w/lowering springs pink, swift...etc(I use RS*R),

-JDM RSB(i use cusco rsb, but unless you like extra oversteer pair it with the front sway bar. And on my RSB, i also made a DIY antilateral lock with parts from Home Depot, but i recently found out that whiteline makes them too),

-Postive Castor bushings(Superpro, avo, perrin...). OEM is too soft and most people like myself find the oem one pretty beat up before replacing it. I replaced mine around 30k mi at it was torn.

Also, because of the softness of the OEM LCA bushing, it cause your suspension to react a bit slower than your input, even one alignment shop tech told me that i should get it replaced because it will cause the alignment to be a little inaccurate.

-Bushings... swaybar endlinks, steering rack bushing set(i have those, pretty good), and all the other suspension bushings you can find. The oem bushings are mostly too soft they do hinder the suspension's from doing its job, so the more you can replace the better.

-Strut bars, legacies has good chasis, but more reinforcenments the better.

-Alignment, research for good alignments shops in your local area, i go to this shop in covina near where i work, its called Import Car Doctor. Their shop did a few episode on the speed network. They use a $85,000 dollar infared camera alignment machine to align my car to the hundredth of a decimal. That thing is so accurate, even heat wave will cause the measurements to go from 0.00 ~ 0.01!

-Go for wider tires :]

After all these, car is very smooth...

[Underdog]

I haven't read the entire thread...

 

You should have... I have upgraded everything in my suspension (except swaybars) since my original post, which was over a year ago.

 

Seriously though, I appreciate your trying to help.

[outahere]

..........They use a $85,000 dollar infared camera alignment machine to align my car to the hundredth of a decimal. That thing is so accurate, even heat wave will cause the measurements to go from 0.00 ~ 0.01!..........

 

I bet if they set the alignment, then drove the car off the rack, and then immediately back onto the rack, they would get a different set of numbers each time they did that.

[LittleBlueGT]

I bet if they set the alignment, then drove the car off the rack, and then immediately back onto the rack, they would get a different set of numbers each time they did that.

 

yep.

 

In fact I have seen it a few times.

[BT4]

Thanks to all the guys who have given me some insight into solving this problem. My car is in the shop today getting the AVO offset lower control arm bushing's installed along with a tight alignment. The suspension is completely stock and has never received an alignment before. The car has exhibited the side to side behaviour on concrete highways since the beginning. I didn't notice it on my test drive because, like a dummy, I never took it out on the freeway.

 

Anyway, I have my fingers crossed.

[Underdog]

I think you will be pleasantly surprised at the improvement with the LCA bushings and alignment. Try to temper your expectations though, normal driving will be much improved, but the car will still be fidgety in cross-winds.

 

After all the modifications I've done (which now includes whiteline swaybars F&R), the car is very stable in almost all conditions. The only times when it feels "loose" are over bumps mid-corner, and during strong cross-winds.

[Guest]

Regarding high speed stability... tein flex coilovers, lca bushings, rear sti lateral links, front strut bar, swift sway bars = car very stable at 160 mph (on track of course!).

[BT4]

Good to know. If it solves the annoying freeway behavior, I will be happy. Having spent about 15 years away from San Diego when I lived in North Carolina, I was a pretty avid windsurfer and kiteboarder. There are some serious winds on the coast there, and sidewinds pretty much disturbed everyone's vehicles. This is one of those things I don't have to worry about any more in San Diego since being back here for three years I haven't been able to do either of these sports because there is never any wind. Good thing I can surf too...

 

The shape of our wagons is probably a contributing factor to cross wind susceptibility. The side of my wagon has a pretty good amount of surface area and it is fairly vertical. It makes for a very good sail !!

Underdog: Do you have all your mods posted somewhere?

[Underdog]

I do now!

[BT4]

Cool upgrades underdog!

 

Well I just got back from the alignment shop and to my surprise they found the stock lower control arm bushings were torn! The car only has 25k miles on it, and I have never been on anything rough with it. The alignment was off as well. There was positive toe up front and it was not even. Anyway they installed the AVO bushings and aligned the car. The torn bushings definitively explain why it was following rain grooves like a train on it's tracks.

I jumped on the freeway but did not log enough time since it was rush hour, but drove it enough to get a pretty good feel for the results. The steering is noticeably heavier. The front end is quite a bit stiffer and road imperfections are transmitted through the chasis and to my hands quite a bit more now which I don't like at all.

The car feels more controlled and tracks well now at 70 mph only exhibiting a hint of side to side waggle from the rain grooves in the concrete.

 

I will have to drive it some more before posting a review, but I can't help but wonder if a new set of stock bushings and an alignment would have solved my problem to begin with...I went over some rumble strips that are on a bridge near my house. The car was significantly rougher over these.

 

More later.

[Underdog]

The stock bushings are prone to tearing, regardless of how well you treat the car.

 

I also noticed a big bump in NVH after installing the bushings, but I got used to it over time. To me, the increased satisfaction of stability and accuracy from the suspension more than offset the extra NVH. What you may notice is increased chassis flex now that the road forces are being transmitted rather than absorbed.

 

The cusco braces definitely stiffen the chassis, but perhaps you don't want that? It seems like you are dedicated to comfort and slight performance increases and in that regard I would recommend the following:

 

Spec.B Bilsteins and stock springs

225/45-17 Tires

AVO LCA Bushings

JDM Rear Swaybar

 

I think this combo would give you an "OEM+" grand-touring ride that has a better F/R roll stiffness balance, and plush Bilstein dampers with plenty of travel. The tires will have slightly more sidewall than stock which will give you a bit more isolation while still being relatively low-profile (not mushy).

[BT4]

Yeah, you nailed that assesment. I wanted to tune the car for long distance cruising comfort, because I am finding myself traveling all over southern california for my job. It's also an automatic, so even if I wanted a track car, I would not use this one as my modification platform. aNo big deal about the NVH, if I don't get used to it, I will just replace the bushings again with stock. I allready have the 225/45-17 Michelin HX MXM4 which are supposed to be the quietest most comfortable grand touring tires out there.

I was thinking that the stiff chasis, had more potential than most cars to achieve a more compliant ride, yet still be a step above the average family sedan in handling, like a camry or a malibu.

As time and money allow, I will most likely try some Bilsteins or some combination thereof. In the meantime, I am going to keep listening, and learning as much as I can. I may go test drive a couple of cars at the dealer also, just to compare the specb and 3.0r suspension to mine.

[ifbiker]

I realize I'm a little late to the party on this one. A friend of mine has purchased a set of Smart Strings to do home alignments. He also picked up the camber check tool. We have done one alignment with success and my Subie is next. I have searched many threads to try and figure out what the best alignement specs should be. These posts on the iwsti.com site have been an interesting read:

 

http://www.iwsti.com/forums/gr-suspension-handling-stiffening/124888-2008-rear-camber-adjustment.html

 

http://www.iwsti.com/forums/gd-suspension-handling-stiffening/138351-getting-best-alignment-dynamic-camber-analysis.html

 

I believe the rear suspension dynamics are similar between the two cars. The first thread actually recommends removing rear camber because the the rear suspension is able to gain camber as the body rolls. I'm curious to know if anyone knows how much camber is gained per degree of roll.

 

The second thread suggests using camber bolts instead of camber plates to gain negative camber and use the plates to dial in caster. This thread concerns pre 2008 Sti which had much less camber than the LGT, but when they increase camber they are close to a stock LGT so the thread IMHO is relavant.

 

I have much respect for the work Underdog and other have done on their suspensions. What is your opinion to setting toe in all four corners to zero, leaving rear camber at its stock setting, currently mine is at -.5 degrees, and using camber bolts to bring the front camber to -1.5 degrees? I'm running a JDM rear sway bar, stock springs and Koni insert struts.

[ShadowImg]

That's pretty much the alignment I'm running now ifbiker. That along with Racecomp Tarmac 1s set to 12/14 from full stiff front/rear, Cobb F&R swaybars with brackets and urethane bushings. I'm at -1.3 deg camber on FL, -1.5deg on FR, 0 on back, and 0 toe all around.

 

Car is pretty stable at this point, the coilovers did far more than anything else, though the alignment made a noticable difference too. Car is much less susceptible to cross-wind "rolling" now, now I just feel the push but the car doesn't lean over into it.

 

Float is pretty much entirely gone at this point. Only things left I notice is that there's still some steering slop, which is probably a variety of bushings that are still stock.

[SBT]

Two (possibly three) critical pieces WRT the suspension IME:

1. If you drop your car 1" (some say 3/4") or more, install a roll center kit - you'll reduce dynamic negative camber and eliminate bump steer
   
2. Replace the goofy/sloppy stock front LCA bushes with an AVO, Perrin or SuperPro replacement bushing - you'll immediately tighten up the handling , gain on-center steering/feel, and reduce wandering. If you use the offset replacements (AVO), you'll also gain substantial positive caster - at the expense of increased NVH -worth it IMO.
   
3. Install rear Adjustable Lower Control Arms - It'll enable you to dial-in negative camber, beyond what you're able to gain with just the rear camber bolts.
   

Obviously alignment settings are critical to getting the handling that you want. But don't forget to check your tire pressures too. Even 1 psi difference at the rear can cause the car to sway as the rear tires try to synch up their different rotational differences through an LSD rear axle.

 

With steps 1-3 in place, I've found that -.75* front and -1.0* rear camber with 0* cross-camber and 0* F/R toe works really well to dial-in a smooth, tight ride that's really tossable and yet doesn't compromise tire wear.

 

There's clearly other variables, i.e., wheel/tire combinations, different strut/spring or CO combinations, swaybars/braces/endlinks, bushings, etc., that contribute to the bottom line, so YMMV.

[ifbiker]

Just looking at the alignment numbers I would have never guessed this would yield such positive results. My guess would have been a noticable amount of understeer due to the -1.0 degrees of negative camber. The 08 STi folks were indicating they noticed an increase in rear tire wear, do you have any hints of that?

[ShadowImg]

Understeer? No, definitely not understeer. The turn-in is a heavier push due to the camber, but that's just the initial force to get it to turn. As far as rear tire wear, I'm not running any negative camber in the rear, and I also don't really know how you'd identify that over the short term. I'm still on my original tires.

[ifbiker]

After re-reading this thread, Underdog and Whitetiger set camber front and rear equally, Subietonic went with a little more rear camber than front and ShawdoImg went with more front camber than rear. After doing some research, and most likely my knowledge is more dangerous than anything, it seems that the LGT rate of camber gain per degree of body roll is greater for the rear suspension than the front. Those that have increased caster will pick up some negative front camber over a stock vehicle when turning the wheels into a corner. It would seem beneficial to start with more negative camber up front to make up for the slower camber gain rate. Could you guys post your thought process on how you reached your alignment? This will help me learn and get to the right street alignment the first time.

[SBT]

Just looking at the alignment numbers I would have never guessed this would yield such positive results. My guess would have been a noticable amount of understeer due to the -1.0 degrees of negative camber. The 08 STi folks were indicating they noticed an increase in rear tire wear, do you have any hints of that?

 

I had these same alignment settings with my stock wheels and 225/45 tires, and had no tire wear issues. Now that I've upgraded to 18x8 and 225/40, still no tire wear that I can discern. Definitely, absolutely NO understeer and I've yet to get the rear to break loose.

 

With all of the positive caster, you gain dynamic negative camber, and with 0* toe all around, the car is just uber tossable and pure fun on the straights (despite grooved highways), changing lanes (and driving over highway bot dots) or traversing steep, up or down, decreasing radius turns.

 

The steering is heavier (due to the positive caster) but it just contributes to how literally "planted" the car now feels. And the steering reacts much quicker to input, so the best descriptor is that the car can pirouette and exhibit no hesitation, slop, or understeer - if anything, it even has a bit of oversteer, but again, more point and shoot.

 

So here's what I have done, in sequence - with Step 9 finally getting me to the way I always thought this car should have come from the factory - and then I'll be done.

 

1. 20mm JDM RSB and AVO urethane SB bushings

2. 4BoxParts Rear Lower Adjustable Links

3. Spec B Bilstein and Swift Wagon springs

4. AVO F/R adjustable SB links, AVO urethane FSB bushings

5. Whiteline RCK and AVO LCA offset bushings (+6* positive caster)

6. Alignment 0* Toe F/R, Camber -.75* FL/FR, -1.0* RL/RR

7. AVO RSB braces

8. 18x8 forged GTVes with 225/40 MPS A/Ses tires

9. Pull all of the Bilstein bump stops and cut them down by half

 

I think the reason the STI owners are noticing wear is they tend to run higher camber settings, which will contribute to tire wear. That, and the fact that their rear suspension setup is different, means that the same settings from our cars, will tend to increase (exaggerate) the changes on the STI. This is an expectation on my part, given what I know about the 08+ STI suspension v-a-v the 05+ Legacy suspensions, and without any benefit of having actually seen the actual results. So YMMV.

[Underdog]

Forgive me, I have been on vacation for the last week and now that I'm back, I have a ton of stuff to deal with, so I have only given the above posts a cursory glance. Also, I am posting from my phone so my response will be brief until I have some spare time.

 

First off, to ifbiker, going with zero toe (f & r) is the first step for suspension tuning. Tuning, as the name implies, is an iterative process, and you should be prepared to take our suggestions along with your expanding knowledge and hone in on your ideal settings, since they are different for everyone. That being said, zero toe gives you an ideal starting point because it will give you the best possible tire wear all other thing being equal. My rationale for -1* camber all around was simply to eliminate the camber variable while I tune suspension damping and swaybar stiffness. My experiences with this setup should be documented above, if not, it is too much to go into via iPhone keyboard.

 

For the most part though, SBT is right on the money, with only minor differences in our approach and setup.

[ifbiker]

Thanks to all for the feedback.

[RdiggA]

That's pretty much the alignment I'm running now ifbiker. That along with Racecomp Tarmac 1s set to 12/14 from full stiff front/rear, Cobb F&R swaybars with brackets and urethane bushings. I'm at -1.3 deg camber on FL, -1.5deg on FR, 0 on back, and 0 toe all around.

 

Car is pretty stable at this point, the coilovers did far more than anything else, though the alignment made a noticable difference too. Car is much less susceptible to cross-wind "rolling" now, now I just feel the push but the car doesn't lean over into it.

 

Float is pretty much entirely gone at this point. Only things left I notice is that there's still some steering slop, which is probably a variety of bushings that are still stock.

 

 

Please share the secret on how you got 0 camber in the rear being lowered. From your avatar it looks like your pretty low. Im running stock 17's with 1 finger gap all around and my car has -1.4 camber on both rears, after my alignment. My friend and i couldnt get the toe to line up at 0 and the camber. I even have the Perrin adjustable links.

[ShadowImg]

^ Picture is when I was running on stock struts & cobb springs, and yeah it was hugely aggressive lowering. I'm now on Racecomp Tarmac 1s at roughly stock height.

[RdiggA]

ahhh ok thank you.