rage2

I'm having some issues with heavy camber change up front under hard cornering, so I was wondering if any suspension gurus can help out.

First off, here's my suspension setup (up front) :

H&R springs w/stock ride height shims
Koni Yellow shocks (rebound adjustable only)
968 M030 sway bars
*** NO strut brace ***
Alignment set to negative side of factory spec all around
18x8.5 OZ wheels, 235/35-18 tires.

Basically the rears are wearing awesome... the camber change under load is minimal, so cornering stance is pretty much flat. Up front, there's like a 10 degree camber change under load, so I'm scrubbing partly on the sidewall, with zero wear on the inside of the tire. It's pretty harsh, here's a pic :



Now, I'm no suspension expert, but I don't think that a strut brace would help here (I don't think it's the shock towers that are moving causing the camber change). I was about to do a band-aid solution by dialing in extreme amounts of negative camber, but that would make the car undrivable for the street. So before I do anything, I'd like some advice as to what's going on here, and what's causing this effect.

I don't remember such huge camber change when I was running 16" wheels... could it be the weight/width of the 18x8.5 wheels that's causing the suspension geometry to go all out of whack?

Thanks in advance to anyone that can help!

RPG951S

I'm no guru , but I'll give my .02c...

First off, I don't think the stock alignment specs are at all suitable for track work. A big factor in alignment settings is the type of tire your using... Hoosier? RA1/032R? or Street tire?

As a data point, I went from pure stock settings to the follow (up front- Using 225/40/17 RA1's[track] & 225/40/17 AVS[street] ):

-1.5º camber
0 or 1/32 toe in
3º+ castor (or as much as I can get on each side)

This is a MUCH, much more suitable alignment for track work; you sacrifice a little straight line stability (but it's still good at 250+kph) for much improved turn in, and it's better for the tires too boot.
For a while, I was running -2.5º camber, but it made street driving a little too exciting
Before shelling out big bucks, I'd start with more suitable alignment setting, and see if this helps with your problems.....

Hope this helps!

adrial

How much tire pressure are you running in the front?

Running stock camber, I was having problems demolishing the outer edge of my tires...

Now, running ~1.5 degrees...sure, its still wearing the outside more than the inside...but I think street driving will equalize it all out. (Street driving will wear the inside more than the outside because of the camber)

Konstantin

what kind of strut bearing do you have?
what about the ruber pieces on the suspension? new or old?
A strut brace would help too.
you also need at least 1.5 degree front

mikjel

RPG951S wrote:

"-1.5º camber
0 or 1/32 toe in
3º+ castor (or as much as I can get on each side)"

IS THE CASTOR ADJUSTABLE?

Konstantin

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by mikjel:
<strong>RPG951S wrote:

IS THE CASTOR ADJUSTABLE?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">yes!

alkemyst

On almost any car (via the shop manuals) Caster, Camber, Toe, etc can be adjusted...sometimes however on certain cars slots must be cut (full instructions down the the millimeter have always been provided in every factory shop manual I have seen).

I would try a strut brace though...I have always been amazed at what they do. However one caveat...whenever you stiffen up you car you allow minor accidents to become major ones. In a 66 Mustang GT I used a Monte Carlo brace on (shock towers tied into the cowl with heavy steel), a semi-minor right side fender screwup, ended up shifting my cowl, dash and roof enough to X the whole body, whereas without it, a light frame machine pull on the right front engine compartment would have made it perfect...

Alan C.

Rage,
It's the SDS You don't have it set right.

Seriously, I never got rid of the lean until I went with my new suspension. Motons, Kokeln front and rear bars, camber -3.6 front, -2.7 rear, .03 toe out in front, .03 toe in in rear, caster at 3.5, 850 lb springs front and 700 lb. rear.

Had to do away with the CD player <img border="0" alt="[hiha]" title="" src="graemlins/roflmao.gif" />

Alan C.

Danno

For any kind of track work, I recommend at least -3.0 degrees camber. There's no such thing as a 'compromise' setting that you can use for both street and track. What you'll be compromising (more like sacrificing) is both tire-wear on the street and sub-optimal performance on the track.

May I suggest a set of caster-camber plates that will allow you to quickly change back and forth between street and track settings?

<img src="http://www.gururacing.net/ImagesMisc/CamberPlates.jpg" alt=" - " />

Have the alignment shop set up your 'street' camber setting (around -1.0) with the plates adjusted to the minimum camber setting as shown. Then they can dial in a 'track' setting of -3.0 degrees or more and make a mark on the plate for your reference. Then all it takes it 5-minutes per side to adjust camber to optimal settings for the track.

Our plates also do not lower or raise your car. So if you have stock suspension, no need to get coilovers just to compensate for height changes with caster-camber plates.

Dave E

Doesn't the toe setting change when the camber is changed?

Konstantin

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Dave E:
<strong>Doesn't the toe setting change when the camber is changed?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">thats the problem. the question is what is more important and I think camber is more important in this case.

Konstantin

rage2

Thanks everyone for all the advice, I'll start toying around with camber and castor settings to see how much of a change it will make. I'll also invest in a good strut brace to see if there's anything to gain there as well.

As a side note, the reason I'm looking for a good setting that works both on street and on track is because I've been tracking my SLK 32 AMG a few times this year, and the turn-in on that thing is amazing, regardless if it's a street tire or A032R's (what I'm using now). It's set to about -1.5 up front, and judging from pics taken around corners, there is minimal camber change at high cornering loads, certainly nowhere near the pic I posted of the 951. And the wear on the street is awesome, I wear out all 4 tires evenly.

I thought there was something wrong with my 951... but I guess the benz benefits from 15 years of suspension advancements .

Danno

"It's set to about -1.5 up front, and judging from pics taken around corners, there is minimal camber change at high cornering loads, certainly nowhere near the pic I posted of the 951. "

"I thought there was something wrong with my 951... but I guess the benz benefits from 15 years of suspension advancements."

Unfortunately, due to the ancient MacPherson front struts we have on our 951s, body-lean will introduce a lot of positive camber-change. If we had double-wishbone front suspension (like ALL Ferraris), then we'd have a camber-curve that would stay negative no matter how much the body rolls. To get comparable camber at full body-roll as the Benz, you'll need something like -4 degrees static camber. While you can compensate somewhat for body-roll by dialing in more negative static-camber, this exacerbates the camber problem on the inside tire (which is now severely dragging its inside edge).

Here's another part of the issue:
<img src="http://www.gururacing.net/ImagesMisc/Rage2cornering.jpg" alt=" - " />

The stock 951 comes with really soft front springs (relative to the rear) combined with 2% difference in weight (51/49% F/R) and a downward-sloping roll-axis inclination causes a lot of roll in the front-end (causes longitudinal weight-transfer to the front-wheels as well). A strut-brace won't help you much here; you can use a stop-watch to test. What would really improve your times is stiffer front-springs that's at least twice as stiff as stock. Around 300-lb/in will be close to the maximum you can use on the street comfortably.

This will reduce body-roll and keep the front tires more vertical under cornering to provide a flatter contact patch on both the outside and inside tires. Reducing body-roll also decreases the lateral-shift of the COG-center of gravity. There's a certain amount of latereal weight-transfer due to COG-shift and reducing that amount will help. It's still small compared to weight-transfer due to cornering-G, but every little bit helps.

With just a front-spring upgrade alone, you'll gain about 2-3 seconds/60-second lap.

Danno

Just realized I had some photos that illustrate the various upgrade phases my car went through. These pictures are for relative comparisons only. They do not represent nth-degree precision due to different cornering-speeds and corners. But they do show the progression of upgrades well.

First, I went from the stock 951 suspension, don't have a picture of that, so stock TurboS is pictured on the left (Remember that one magazine article where they said they could gauge the cornering limit of the 951 by the sound of the rocker-panels rubbing on the ground?):

<img src="http://www.gururacing.net/ImagesMisc/BodyRoll-StockTurboSvsM030.jpg" alt=" - " />

On the right, I had upgraded my car to 200-lb/in springs using <a href="http://www.paragon-products.com" target="_blank">Paragon Product's</a> coilover kit. Also had the 968 M030 swaybars installed. As you can see, the cornering attitude and lean is similar to Rage2's car. But I still had too much front-end lean and the resultant positive-camber change issue.

So I installed 350-lb/in springs along with the Weltmeister swaybar set:

<img src="http://www.gururacing.net/ImagesMisc/BodyRoll-TurboWeltvsE46.jpg" alt=" - " />

Body-roll has been eliminated to practically nil, especially compared to the stock E46 M3 that's going around the corner in the exact same place and speed I did. However, the E46 M3 can obtain identical cornering powers with a much, much more comfortable suspension (like the SLK Benz).

Mark G

Alan C. has the right idea. I had incorrect tire temps in the front showing too little front camber with -3.1. Went to -3.6 for the last weekend in Seattle and was much happier. Tire temps and wear much more reasonable in spite of still being too soft in overall spring rates. I still run stock class PCA so have only 450lbs front and 30mm tb in back. Konis(argh). M030 bars. 275/40/17 Hoosiers. Hope this helps.