In search of high-speed stability

I need to find a way to correct the wandering feel the GT has at highway speeds. I often find that the car will pull mildly on either side of the crown. Going over bumps, I can feel the resistance change in the steering wheel from one direction to the other. On long stretches of banked roads I feel like the wheel is of 5-10 deg from center in order to go straight (or what feels straight but is probably a long sweeping curve.) Sometimes the car will "dart" in response to minor changes, most likely due to small steering corrections AND a bump. I find that most of these symptoms only occur at speeds >60mph. However, the pull due to the crown of the road is noticable at lower speeds.

Maybe it's something that can't be fixed but I believe it has to do with either:

1) Caster, or

2) Scrub Radius

My best guess is that by increasing caster (through the fulcrum bushings) the car will have a better on-center feel at the expense of increased steering effort.

So, if you have noticed this issue and have an informed opinion or have resolved the issue, please post up.

-Rick

There's nothing you can do about the crown of the road. Physics at work. The banking is causing the car to slide downward, hence you have to steer opposite. Nothing you can do about it. By turning slightly, you also take up some of the preload in the tires, making them more sensitive. Remember the NSX with the 10,000 mile tires, the suspension is set up so all the preload is taken out making it really quick steering.

Bump steer FTL. Generally unless the wheels are pointing straight ahead, you will get bump steer if the suspension moves. Just geometry at work. All the pivoting axis on the chassis side, must line up in a straight line. If the steering tie rod is not in a straight line, any movement will translate into the wheel turning to one side or another.

the "wander" syndrome = at speeds of over 60 mph, the car "wandered" from side to side, almost like small "twitches" as if buffeted by winds.

Exactly the symptom.

Here are the results of my last alignment:

After:

Left Front.............Right Front

Camber: -0.3°......Camber: -0.2°

Caster: 6.4°.........Caster: 6.0°

Toe: 0.02°............Toe: 0.02°

Front:

Total Toe: 0.04°

Steer Ahead: 0.00

Left Rear...............Right Rear

Camber: -0.7°.......Camber: -0.6°

Toe: 0.09°.............Toe: 0.07°

Rear:

Total Toe: 0.17°

Thrust Angle: 0.01°

The before specs are also listed here.

Since this alignment I have gone from Wintersport M3's on stock wheels to Toyo T1-R's (225/40-18) on Rota Tarmac2's (18x7.5 e48).

Some alignment / tire shops will give you a free measurement for free. I would take the car to another shop and have them measure it for you. It really sounds like an alignment issue.

My car is really stable at high speeds.

Exactly the symptom.

 

Here are the results of my last alignment:

 

After:

 

Left Front.............Right Front

Camber: -0.3°......Camber: -0.2°

Caster: 6.4°.........Caster: 6.0°

Toe: 0.02°............Toe: 0.02°

 

Front:

Total Toe: 0.04°

Steer Ahead: 0.00

 

Left Rear...............Right Rear

Camber: -0.7°.......Camber: -0.6°

Toe: 0.09°.............Toe: 0.07°

 

Rear:

Total Toe: 0.17°

Thrust Angle: 0.01°

 

The before specs are also listed here.

 

Since this alignment I have gone from Wintersport M3's on stock wheels to Toyo T1-R's (225/40-18) on Rota Tarmac2's (18x7.5 e48).

I will bet you a box of donuts that your problem is the rear R toe being off. Actually, I am pretty confident this is your issue. Shoot for your F and R toe to be as close to 0.00 as possible. My rear R toe was off at 0.11 before it was fixed. I drove like this for a while, pissed at the wander. Aligment made everything perfect.

Here are my AFTER specs (used your template ):

Left Front.............Right Front

Camber: -0.7°......Camber: -0.5°

Caster: 6.1°.........Caster: 5.6°

Toe: 0.00°............Toe: 0.01°

Front:

Total Toe: 0.01°

Cross Caster: 0.5

Cross SAI: .2

Left Rear...............Right Rear

Camber: -0.9°.......Camber: -0.4°

Toe: 0.01°.............Toe: -0.01°

Rear:

Total Toe: 0.01

Thrust Angle: 0.01°

Cross Camber: -0.5

The Fulcrum LCA bushes definitely help. But surprisingly, fitting a larger rear sway bar helped a lot too - subtle rear roll caused wander at speed.

Get the LCA bushes & a decent alignment & come back if there still are issues.

Hmm, that sounds like a plan. I was planning on saving the bushings until I did my suspension build in a year or so (going to get the aluminum control arms), but for $100 and change it seems worth it to do it now.

The real question is: Where do I go for the best installation & alignment?

Watertown Tire did my first alignment (above). They scratched up my stock wheels during mounting/balance/rotation and their alignment readout seems to be missing some info compared to LawGT's.

Direct Tire mounted my Toyo's on the new wheels. They did a great job but I've never used them for anything else.

Cityside Subaru, the dealer I go to for oil changes. They would be the most familiar with the car and would be able to take care of some other issues while I'm there.

Opinions?

Get it aligned at the dealer. There is where I go for mine, and in my area, the dealer's 4 wheel aligment is actually cheaper than other shops. My recomendation would be to do the aligment first. Mine was not perfect either (yes, I'm anal), bec I would have wanted the camber to be the same on both sides, and toe completely at zero (but they are very close, which is still fine).

My understanding of the fulcrum LCA bushes is that they are used to increase positive caster (which is not otherwise adjustable by aligment) or to balance it out from one side to the other in cars that have the caster way off. More positive caster "pushes" the F wheels forward in the wheel well (some quite noticeably) and increase the "heavyness" of the steering (think BMW). (pls correct me if I'm wrong). I seem to recall some threads in here re the bushings, some singing its praise and others more of a mixed bag.

Yeah I like the dealer option the best. I'm not too keen on having them install the LCA bushings though.

I think the bushings should be done at this point to help the car track properly. With stock caster the steering seems to be pushed by the momentum of the car.

Get it aligned at the dealer. There is where I go for mine, and in my area, the dealer's 4 wheel aligment is actually cheaper than other shops. My recomendation would be to do the aligment first. Mine was not perfect either (yes, I'm anal), bec I would have wanted the camber to be the same on both sides, and toe completely at zero (but they are very close, which is still fine).

 

My understanding of the fulcrum LCA bushes is that they are used to increase positive caster (which is not otherwise adjustable by aligment) or to balance it out from one side to the other in cars that have the caster way off. More positive caster "pushes" the F wheels forward in the wheel well (some quite noticeably) and increase the "heavyness" of the steering (think BMW). (pls correct me if I'm wrong). I seem to recall some threads in here re the bushings, some singing its praise and others more of a mixed bag.

I still haven't heard anyone criticise the LCA bushes (aside from the OEM ones )...the increase in steering weight is hardly a huge change & certainly the light Subaru steering can afford it!

I know you're trying to help, but check post #4...

As far as the road conditions, It happens on any stretch of freeway I can get upto speed on. The wandering feeling is always there at those speeds and the pull happens pretty much on any road that is banked/crowned and any speed above maybe 30mph.

I still haven't heard anyone criticise the LCA bushes (aside from the OEM ones )...the increase in steering weight is hardly a huge change & certainly the light Subaru steering can afford it!

I said "mixed bag" and to my recollection . I agree that the LGT can use more weight in the steering. BTw, how much more caster do the bushings add?

Non-offset, about 1/2 a degree - offset about 1 degree.

Thanks. My caster is off by exactly .5. Hmm... I need to look for that thread where you detailed the install. Are there any drawbacks by using the bushings?

Also, I looked up BMW's settings (just because I LOVE the steering weight it the 3 series BMW's) and here they are (according to a bmw forum). the 3 series caster is wayyy higher than ours:

BMW recommended specs for the E46 M3:

Front:

-------

Camber: -1.3 to -0.7 degrees

Caster: +6.9 to 7.9 degrees

Toe in: 0.08 to 0.19 degrees

Rear:

------

Camber: -2.0 to -1.5 degrees

Toe in: 0.13 to 0.23 degrees

Nope - I've had no drawbacks - and this is over 20,000km later. Here's the thread:

http://legacygt.com/forums/showthread.php?t=44834&highlight=fulcrum+lca

Aerodynamics

The car has a cd of .29. The car is very smooth and the only anti-lift or stability feature is the undertray.

Add a front spoiler and a rear lip. Don't get anything crazy, just somthing to break up the vacuum created by the air going over the roof of the car. The chin spoiler will help keep increase stability and keep the nose from lifting. If you took off your undertray, then you might want to put it back on.

Alignment

If you want straight line stability, then make sure you have some toe in on the front. This will decrease the cornering stability, but increase the straight line stability.

Bushings

Get the whiteline legacy specific ksr 207's and either the Fulcrum or AVO LCAB bushings from rallitek. These made a tremendous improvement.

Tires

Stay with the stock width. The wider the tire, the more drag and lift unless there are accompanying airodynamic mods like strakes.... etc.

It's been a while, but I have an update...

I am currently running on: Konis/Swifts, Spec.B lower control arms, AVO LCA Bushings (increased caster), and the Whiteline Roll Center Correction Kit. My impressions thus far are based on the ride with 225/40-18 Toyo T1-R UHP Summer tires.

Regarding my statement in the OP:

I often find that the car will pull mildly on either side of the crown. Going over bumps, I can feel the resistance change in the steering wheel from one direction to the other. On long stretches of banked roads I feel like the wheel is of 5-10 deg from center in order to go straight (or what feels straight but is probably a long sweeping curve.) Sometimes the car will "dart" in response to minor changes, most likely due to small steering corrections AND a bump. I find that most of these symptoms only occur at speeds >60mph. However, the pull due to the crown of the road is noticable at lower speeds.

The addition of the Bushings and RC Kit has all but eliminated the need to counter-steer due to the crown. I can still feel the wheels wanting to follow the crown, but if I hold the wheel straight, the car goes straight, which is all I ever wanted. It feels like the "slop" of the stock LCA bushings was allowing deflection that necessitated the 5-10deg counter-steer. I also like being able to feel the force being exerted through the steering wheel as it makes me feel more connected to the road surface.

The Roll-Center Kit has definitely improved (reduced) the bump-steer response. In stock form, and even more so when lowered, the car would dart around when the front wheels hit bumps individually. Now the car will continue to track straight over pretty much any road imperfection, without passing too much NVH through the steering wheel.

I have not noticed the "twitchiness" (which was my biggest gripe with the car) since installing the LCAs/Bushings/RC Kit, but it mostly happens during strong crosswinds so I'm not ready to say it has been completely eliminated. However, when the car was just lowered there were a few times where the twitchiness occurred and was just as bad as stock, so I think we can rule out the stock springs/dampers as the "cause". I am hopeful that this has been cured with the new additions, and will check back after some more time.

My conclusion thus far is that while lowering the Legacy on appropriately stiffer springs and dampers greatly improves the performance/comfort trade-off (IMO), the addition of the LCA Bushings and RC Kit complete the transformation from "sloppy" to "sporty".

Nope, I bought the arms used with the AVO Bushings, from Legacy_Otaku.

I think it is speculation that the spec.b arms come with different bushings than the stock GT arms. Also, I cannot attribute how much of the benefit is due to the stiffer material, or the increased caster (+0.3 degrees each side).