[jared57]

After doing some thinking about my current alignment/supension setup, I decided to ask you all for opinions and advice.

I blew through a set of 255/40-17 RA1's faster than I thought I should have. I think the reason is because I have too stiff a front bar for my alignment/tire selection. I think that the front bar is overpowering the front tires (rears wear perfect). Note that my RA1's only see track use. Buttonwillow, Willow Springs Big Track, Streets, and HTM.

I have JDM pinks. In the front am running -2.4º camber with 1/32" toe-out, and in the rear -1.85º with 1/32" toe-in. (Note: I am obsessed with keeping my pressures under control and I check tire temps at least once each track day. So take that out of the equation.)

For my last 5 track days, I had my Whiteline Race front bar (XSF36XXZ) set to full stiff (29mm) and the Whiteline Race rear (XSR37XXZ) set to full soft (27mm). It felt great, very balanced at high speed and lower speed tight corners. Tire wear and temps on the rears is great and even across the tread. The front is a different story. I was burning off the inside of the front tires. So, I set the front bar to the soft setting and set the rear to the medium (28mm). The car began to understeer slightly. Tire wear in the front was much better, and the rears ran hotter but still wore even (temps front to rear were closer, a good thing).

That said, I think that I want to try putting the front bar back on the stiff setting and remove some negative camber up front, maybe go to around -1.8. I figure this will keep the contact patch flatter because the stiffer front bar setting is reducing the roll. This should give me MORE front grip. What do you think? Is my logic correct? Or do you think this may add even more understeer because of the reduced camber? Maybe I should remove a little negative camber from the rear too.

Any other suggestions? Thoughts?

I think that ultimately the best solution is in having stiffer springs to control roll instead of just a really stiff bar. Well, make that a better balanced combination of bars, springs and dampers to control roll. Yes, coilovers are in my future, but for now I want to have the best setup I can with my current hardware. As it stands, I am faster than most stage 2 sti's with coilovers anyway!


Thanks!

[javid]

I would run 0 toe before trying different camber. You sure you only have 1/32 out? The wear makes me think you have 1/4 or more.

I also use RA-1s alot. I have 700lb front springs, 24mm bar, -2.5 to -3.3 of camber and it wears fine. I have done that to a tire because I didn't realize / fix about 1/2" of toe out and put 1000 miles on the car...

You probably know this but changes in camber at the strut tops will create changes in toe. Just a guess / thought.

[jared57]

Good point... I will double check what the current toe really is before I reset anything. Thanks Javid.

[sti206]

keep updating i just got the 29mm but have not install. not sure if i should!
I got 27mm in the back .do i need to replace my otormount as well??

[Greg]

Originally Posted by jared57

Tire wear and temps on the rears is great and even across the tread. The front is a different story. I was burning off the inside of the front tires. So, I set the front bar to the soft setting and set the rear to the medium (28mm). The car began to understeer slightly. Tire wear in the front was much better, and the rears ran hotter but still wore even (temps front to rear were closer, a good thing).

Kudos to you for taking tire temps! Actual real world measurements is something we don't hear enough about. I'd give you bonus points of you posted your measured number for all 4 wheels!

Regarding your issue, I think Javid hit the nail on the head. If the inside of your fronts are overheating and wearing quickly its either too much camber or too much toe. -2.5 in the front, seems to be right in the "normal" zone for track use, so I doubt that's the issue. Any amount of toe in the front will add heat to the inside of the tire. I think before you change the camber settings it would be good to get pyrometer readings with zero toe in the front. That way the measured contact patch are not being influnced by the toe settings. Once you get the contact patch squared away, you can add some postitve toe "too taste", bearing in mind that it comes with a cost, tire wear.

The other trick I've heard of (but haven't need to do) is to have the tires remounted on the rim swapping the inside for the outside. That helps with the tire wear. I don't think this can be done with every tire, so validate that with your tire vendor, or ask in the tire forum before spending the money on the mounting and balancing job.

Keep up the good work, and let us know how this turns out.

[STI 2004]

I would guess it is the toe out causing the inside tire wear. With soft springs under braking you will also be putting additional load on the front, which will cause additional toe out as the suspension compresseors.

I would run 0 toe up front or slightly toe in to help deal with the braking toe out effect.

N.

[jared57]

STI 2004... Interesting thinking!

So, soft springs allow more toe out under load. This includes heavy braking and I would imagine long sweeping high-G turns. One thing to note is that the majority of the wear happened at a very high speed track, Willow Springs International.

Now my first question is this:

How much dynamic toe does the STI supension allow? I know that soft or compliant suspension bushings affect dynamic toe. This is summed up well by the guys at Advance Racing Technology:

It should be noted that in recent years, designers have been using bushing compliance in street cars to their advantage. To maximize transient response, it is desirable to use a little toe-in at the rear to hasten the generation of slip angles and thus cornering forces in the rear tires. By allowing a bit of compliance in the front lateral links of an A-arm type suspension, the rear axle will toe-in when the car enters a hard corner; on a straightaway where no cornering loads are present, the bushings remain undistorted and allow the toe to be set to an angle that enhances tire wear and stability characteristics. Such a design is a type of passive four-wheel steering system.

Passive 4-Wheel Steering? Very interesting potential for suspension tuning.


Next Question:

I have been told that setting static camber at the strut top using a camber plate will affect toe settings more than adjusting it at the bottom using the offset bolt. Does this then mean that setting camber using a camber plate will affect dynamic toe more than an offset bolt at the knuckle? Maybe more tuning potential here too.


Lastly:

How does the amount of caster on the STI affect dynamic Toe? I have the Whiteline ALK. So I have more positive caster than stock, should be around 5º. Does adding positive caster add more dynamic toe?

[Greg]

Originally Posted by jared57

Does adding positive caster add more dynamic toe?

I think the proper term is "bump steer" and yes adding more caster will give you more bumpsteer. I don't believe adding more camber using a plate will give you more bumpsteer, as compared to using a bolt. However using a plate will reduce your dynamic camber unless you also add more caster in at the same time. But then you are adding more bumpsteer. Its a balancing act.

Here's chart Nhluhr created while ago to illustrate the changes to bump steer by adding 1.5 degree of caster. Hope he doesn't mind me adding the link.