i'm not a canyon racer, real racer, or really hard street driver, so i'm asking if this impression i'm getting is imaginary or founded in real car dynamics:

i have eibachs on a 2003 mcs with 4 h sport control arms and 100+ lbs. out of the rear.

the stock camber was -.2 at the front and -.8 or -.7 at the rear. i noticed trailing throttle oversteer.

now the front camber is at -0.9 deg. with the rear camber at -1.6, the (wuss driver) trailing throttle oversteer seems much less. it also seems less than when the lowered rear camber was -.9.

the car feels much more secure at -1.6 rear camber. does the increased rear camber give lower trailing throttle oversteer or is this an imaginary effect from my lack of experience with the car at the limit?

thanks

 

I had the same experience when going to H&R springs. I do not have camber correction arms and the camber is just shy of -3 degrees in the rear. The fronts about -1.2 and the threshold went up a good amount and balanced the trailing throttle oversteer out a bit. I can still get the back end to squirm and get real light if I slightly let off or add some quick input mid-corner, but it's definately more composed.

 

I would check your toe settings as more rear toe out will induce oversteer, and converse.


in the front, changing camber to more negative will also make toe more negative, due to the geometry. In the rear, simply lowering the car will make camber go neg, but I don't think toe will change.

In any case, you should check your toe settings. I'm using 0.0 toe, front and rear, -2 camber front, -1 camber rear.

 

All,

Just my thoughts, and I may be off the point. Before I replaced my stock rubber bushed rear control arms with heim jointed arms, I was noting "trailing throttle" lateral oscillation of the rear end suspension especially when cornering near the limit. The rear end felt to me like it was wobbling from side to side and the chassis tended to oversteer. Scared me a couple of times. After I replaced the control arms with the heim jointed arms the lateral oscillation disappeared and the transient oversteer disappeared. My take is that the camber and toe alignment discussion is useful, but, doesn't get to the heart of the problem. I believe that the problem that you are noting is rear suspension compliance. In a situation of cornering under trailing throttle the rubber bushings alternately load and unload and rear traction is compromised. Alignment and measures to reduce unwanted suspension compliance would be a more complete solution.
Let me know what you think.
Regards,
John Petrich in Seattle

 

John,
Did you replace all four rear control arms? Also, if you replace all 4, do you have xenon lights? Was wondering what you did with the upper driver side control arms w/ the black box for the adj of the headlights.

 

Your oversteer is a function of your front and rear toe, spring rates, shock settings, camber, weight distribution, tire pressures, tire compound, track/tire temperature, and all the stuff Petrich and jlm mentioned.

If all you did was change the springs and rear conrol arms you would have decreased front toe and camber (added understeer), decreased dive on lift (more camber in rear)(added understeer) and added camber in the rear (more oversteer). If the affects of the first two exceed the third one your perception may be correct.

I've had a lot of fun and frustration over the last year or so figuring out how to set up the car for Ax and differing tracks and conditions. You can do a lot with tire pressures and camber but the easiest way is with shock settings.

 

i don't know if this will help anybody's thinking:

i mistakenly listed my current rear camber at -1.6. it's really -1.8

the front toe has stayed the same as close as i can measure by hand: 3/32" toe in.

my stock rear toe was just under 1/16" toe in. now it's 0.

the 4 h sport control arms were the "new" oval tube end style.

i know that the swaybars also play a factor, but jlm, is your setup with more front camber than rear camber intended to reduce understeer? or has it something to so with turn in?

thanks again for the advice

 

Correct me if I'm wrong but...does higher front pressure/lower rear pressure enhances oversteer (everything equal) or vise versa?

 

Yes. :smile: because your rear's sidewall will squirm more and loose structural stability.

 

John, i have the h-sport control arms (bushings) and experience the same lateral oscillation, or sponginess may be another way to look at it. I've considered heim-joint units but one thing bothers me: street use.

I am concerned that under cornering, if one hit a hole with cornering forces on the outside bar, how well do the heim-joint units hold up to that abuse? And the mounts themselves? I have this vision of breaking something. At least bushings will absorb the shock. Is this a valid concern on my part?

If not valid, my H-sport control arms (one set) are for sale. :smile:

 

Monkey Boy,

My theory is that the "lateral oscillations", as I call them, are the product of the bushings loading and unloading with lateral acceleration causing small changes in the alignment settings that in turn alter the attitude of the chassis. I also appreciate your concerns about the potential impulse absorbing benefits for the suspension from the bushing compliance. I have almost 10,000 miles on my Alta heim jointed arms. Also, I am also a maintanence NUT and am always checking the suspension for signs of wear, deformation, etc. I recently took the lower arms off to do some maintanence and could not detect any sign of undue wear in the joints. I have not had any component failures of related suspension elements from impulse loading. In the past, I have complained to John, "jlm", about "clunking" as I drive. What I found a couple of thousand miles ago was that one of my solid sway bar links had stripped threads and had come loose. Replaced that link end and all the "clunking" has disappeared. I don't think that I am picking up much noise from the solid locating links.
Overall, I am very satisfied and don't feel that I have lost anything in the ride or reliability with my solid joints.

Regards,
John Petrich in Seattle

 

john:

did you ever change out the rear trailing arm bushings (for Powerflex urethane?) I have a set, but haven't taken out the arms yet to swap. Maybe then I'll look into that spherical ball solution, eh?

after reading your report, i may go to rod ends for the rear contol arms, although there are powerfex inserts available for the stock bushings.

 

Quick question Blue:

I'm confused with your series of statements above. In one case you say that more camber in the rear gives more understeer, and then you say that added camber in the rear gives more oversteer.

Please explain.

Thanks,
BB

 

you get more oversteer when the front traction exceeds the rear traction. you get more understeer when the rear traction exceeds the front.


increasing camber only helps if it increases cornering traction which is a combined result of many suspension elements as well as fwd/rwd, tire pressure and compound, weight distribution and throttle application. IMO, the best approach is to maximize wheel traction by optimizing camber and tire pressure, then balance oversteer/understeer with sway bars and shock settings

you could have too much camber if your roll stiffness is greater compared to a car with the same camber and less roll stiffness.

 

I recently decided to try my H-sport Front swaybar on the Stiffer setting. Everyone said it would cause more understeer or push.

What occured was better grip in the front end -- and because the front had better grip the rear was rotating more - I then had to adjust the rear swaybar (H-sport comp) from the stiff to middle settings and be very conservative with the rebound settings on the Bilsteins.

I learned this by spinning the car on corner lift several times (I'm a slow learner)

Because I have my suspension now tuned a specific way, rebound adjustments on the shocks make a huge difference in handling, and I'm learning through trial and error when and how much to make these adjustments

I will add that all of this learning and spinning took place on an autox course

 

John (jlm),

Haven't installed the PowerFlex bushings on the rear trailing arm bushings. Just got my Service Manual from Amazon and wanted that book in hand before I take that project on. That might have been a mistake. For instance I don't know how to follow the instruction to "tighten control arm mounting bolts only after vehicle is placed on ground and loaded normally". Gads, do they think I am an ant?

Am still interested in the rear trailing arm spherical bushing idea that we discussed earlier this year. Really appreciate the spherical bushing arrangement in your front camber plates. Some more experienced MINI drivers who have driven my MINI on the track have commented on the "directness" and "responsiveness" of the front end.

I'm interested in the spherical busings.

Regards,
John Petrich in Seattle

 

This makes more sense to me. Given that I have a relatively stock suspension setup (only a rear sway bar), my next suspension change was to add front camber plates to increase front traction and then readjust my sway bar to balance out the car.

JLM, I know your car is pretty heavily modded, and you have lots of experience with the suspension. After the camber plates, would you recommend new springs, or rear control arms ?

BB