Something in your setup is goofy. The spring rates are an issue for sure. Due to mech advantage the stiffer spring should be in the rear. The Perrin psrs with offset and caster-camber plates all set for max caster will help the fronts. But if you need to run 5 or more camber, in the rear?!? What tires? Hoosiers?

 

I just bought the AFI adjustable LCAs and DME toe arms from deylag. The reason I went with them is that given my ride height and desired camber, I can't get the toe I want. The alignment tech told me either I would get the camber I want, or I would get the toe I want, but not both (with the stock setup). My rear camber is around -3.0.

 

Yeah road race setup will be significantly different than autocross. I am running similar times to the 996 porsche cup cars. I run full competition slicks, they require a lot more camber than r compound tires. Michelin recommends -3.5 to -4.5 optimal camber settings, and they have a lot stiffer sidewalls than others, Pirelli for example require more camber as they are super soft. I don't need -5 in the back, i said above i will probable need 1/2 to 1 degree more in the rear based on how they are wearing right now. It's really not out of the ordinary for the whole setup.

Stiffer rear springs is the first I've heard about that, my front to rear weight distribution is quite a bit heavier in front so it seems logical to have stiffer fronts, no? My corner balance (me in the car, 5 gallons fuel) is as follows:
LF: 893 RF: 884
LR: 590 RR: 550

As far as overall feel of the car, it's really neutral and feels great. I am not overdriving the shocks or springs, but I still want to play with different rates also. I'm sure I can improve the setup all around, and that's what I have been doing with the car over the last couple years. I'm not disagreeing with you guys, and am enjoying this discussion, thanks.

 

AS far as spring rates front to rear are concerned the reason you want stiffer rates in the rear has to do with the suspension geometry. We have a McPhearson strut front and Multi-link rear. If you look at how the control arms are attached you will see that the rear is mounted more inward such that there is more leverage which requires a stiffer rate to compensate.

Now these isnt a one size fits all rate as depending on driver preference as well as weight reduction which you mentioned these all come into play.

Personally as I mentioned prior I would suggest upping the rates in the rear for starters and see how the car responds to that. From there I would tweak the alignment and dial in more camber.

 

Heel2Toe is right. It all has to do with the different type of suspension in the rear. it is a multilink with much different leverage. Typical rates are 10K front 12 k rear so about a 2 k difference f to r This will give the correct motion ratios. This will help reduce any roll couple induced by the different motion ratios front to rear. However each car is different as is the application . Some are using 12k/14k others 8k 10 k. I would not want to go too high a rate in the rear causing the car to oversteer at Cup car speeds. That would be expensive. And of course the alignment and sway bars must then be looked at to re-establish the handling balance, effective use of the tire, and turn-in.

 

I actually created a simple spring rate calculator on Google Docs a while back to try and figure things out a little better than trial and error. The front/rear motion ratios I used were based on figures I've read either on this forum or somewhere else, I can't remember. Someone like DallasJ probably has done all the legwork to actually figure them out.

https://docs.google.com/spreadsheet/...kE&usp=sharing

 

if you lower the rear ride height you can get more negative camber out of it. I've measured up to -3.6° but you can only go so low before you max out the articulation of the upper ball joint. stiffer rear springs will help you get low without maxing the ball joint. i probably wouldn't go any stiffer than a 26k rear spring with a 27mm rear bar though.

 

Is that a typo?

 

Thanks for the info guys, I knew we had multilink rear haha. I just didn't know that the motion ratio for the springs were different, but that makes perfect sense.

 

update on my car, and now more confused. I have 16k rear springs, green tein with stamped part number. i have no idea what my front springs are, they are black and have no markings on them at all. i would think 16k rear is plenty of spring rate, but i'm still getting outer shoulder tire wear, i think it just needs more camber still.

 

You might want to find out what the rates are for your front springs. And have you messed around with tire pressures? Maybe you do indeed just need more camber but I think you should get your rates figured out first then go from there.

 

What size tires and width wheels? Are you getting rollover on the outer edge?

 

yeah there's a shop here that should be able to measure the spring rates for me. and yes i work with tire pressures, typically 28-30 hot.

18x10.5 with 280/650-18 (varying), the tires aren't bulging/rolling over, just outer shoulder wears more than inside in the rear. fronts wear really even across the whole tire.

 

I have agency power lower control arms, and megan toe arms and their both great products.

 

how much negative camber are you able to get out of them?