I am disappointed at the amount of responses and everyone just wants to throw money at the problem it seems.

Your ride height looks too low in those pictures. What is your measured gap from wheel to fender both front and rear?

I agree with 03whitegsr that it would be helpful if tire makers would release spring rates that work with their tire. Most times if you call the manufacturer and get someone in their motorsports dept that can tell you what spring rates you should use for that tire.

 

From center of hub to fender lip, its 13" front, 12 3/8" rear.

 

i agree, and as i said in my thread i think the approach to spring son an evo needs to be modified slightly due to the high end "street tires" that we are all now running

i was just using the dymanics calculator on the autocross to win page.

 

It's relatively cheap to buy a few pairs of springs and try them out. Even if you end up back with your original spring rates, the knowledge and experienced gained in the process of trying different rates goes a long way.

There is no one-size-fits-all solution here. The math and experience will provide you with a good starting point, but it can't take into account all of the variations in driving styles, surfaces, venues, etc. At some point, trying different variations is the best way to figure out what works best for your individual situation.


As for ride height: Do you have any pictures of the car at steady-state on a flat, level surface? It's tough to tell from the pictures with cornering and/or dive.

 

Construct, Post #6 has some static pictures.

 

I'm no mathematical expert or Engifineer, just a Liberal Arts graduate who does a lot of reading, a lot of discussing, and has tried things. And I'm more of a reader than a commenter on this forum so my voice may not be as respected as others, but I'm not some newb trying to sound official.

I think your ride height is just fine and center of gravity should take priority over perfect geometry. [pause to let people balk and scorn]. Sure, your roll center may be below the ground but lower center of gravity= reduced weight transfer. There are respected suspension mathz people who advise this approach (even people on this forum), I've found benefit in the approach, and others have tried it too, saying the lower they went, the better the car felt, despite having "incorrect" geometry.

I think you can go higher in spring rate. My coilovers are directly from an Evo which placed second (by like 0.01 of a second) in STU at Nats a couple years ago, and the spring rates are both higher and have a bigger delta from front to back. By that I mean higher than 12/14, and a bigger delta. Again, not what the vocal theme has been on here but I have a few reputable sources that say it's worth trying. Granted, I'm speaking to autocross specifically and road racing may not benefit from the same setup-- what could help an autocross car rotate could make a road course car a handful of oversteer.

I run swaybars only slightly stiffer than stock (in the teens of percentages) and stock swaybars were used on the STU car which previously ran my coilovers.

For a cheap and quick solution, I'd suggest trying more camber up front, maybe a little front toe out, less camber in back, and no rear toe.

You might also consider wider tires to reduce sidewall flex-- I'd say 9" or 9.5" for a 245 tire. An article in GRM found that the same tire on a wider wheel increased responsiveness and materially reduced times. And, again, I've found benefit it and so have other reputable sources.

I don't know how all of this will translate to a massive spreadsheet but who's to say getting your car perfectly setup according to Excel will work with your preferences, your driving style, and driving ability?

 

My knowledge of how the Evo behaves when significantly lowered is very limited. Mostly because I have a terrible driveway and I can't get my car in to my garage if I go much lower than stock.

But my understanding (which could be very wrong here, so be warned) is that lowering the car too much results in:

1) A roll center that is relatively quite far from the center of mass and
2) The suspension geometry operating in a range where the roll center tends to move around a lot relative to the suspension travel.

Having your roll center and center of mass farther apart results in more body roll for a given cornering force. However, upping the spring rate and/or swaybar rates will offset the increased body roll. It's entirely feasible that the net benefit of increased spring rates and a lower center of mass will more than offset any deleterious effects of having the roll center so far from the center of mass.

Having the roll center move around a lot through the range of suspension travel is also not ideal. But again, this can largely be offset with increased spring rates. Higher spring rates translate to less suspension travel for a given cornering force. If your spring rates are high enough, the suspension might not move enough to make this much of an issue.

In short, the theory is that the sub-optimal suspension geometry produced by extremely low ride heights might not be detrimental enough to offset the gains from the lower center of mass if and only if your spring rates (or general roll stiffness) are high enough.

More good data points. And more evidence that there's more than one way to make this all work.

 

You've elaborated well on the guidance/ theory, and maybe I should've elaborated as well. But yeah, the guidance/ theory is to lower it as far as feasible and then make it stiff enough that the bad suspension geometry doesn't really have a chance to come into play.

Not great for a street car, but that's also not part of the consideration or criteria in this discussion, though I follow this same principle and, while I don't DD my Evo, it's still plenty bearable.

 

I figured you knew. I was mostly just thinking out loud here.

I've been surprised at how bearable my 650/700 spring combination on the Ohlins has been so far. It's never going to be as comfortable as more typical street spring rates, but it wasn't nearly as harsh as I expected.

I imagine jumping to the 16K / 900lb range would probably be downright painful for DD use though unless all of your roads were glass smooth.

 

Ive found my 10/12s to be well within the range of daily commuting although I don't drive it more than once maybe twice a week. Its certainly a lot more comfortable than my EG civic hatch that I daily on 450/550s

The 12/14 swifts are on order. One of my motivations is also to replace the generic off the shelf springs Im currently running. With the backorder estimate and my schedule, Im hoping to get them in before going to the Evo school on July 12th

 

This is just from modeling the suspension but geometry wise, bumpsteer is a mess on a heavily lowered Evo. The RCK helps a lot, but once you start messing with caster and SAI the Whiteline stuff can be easily improved upon.

Just my opinion...
#1 Keep the car off hard stops (bumpstops, joint articulation, tire running into stuff)
#2 Keep the natural frequency in a reasonable range for the tire used.
#3 Correct bumpsteer
#4 Get the CoG down
#5 Worry about roll center, anti-dive, caster, etc...

 

Just a quick update.

I installed the 12/14k swifts along with my 18x10s and 285 ZIIs. And in the process raised the car up about 1/2" in the front and 3/4" or so in the rear. Also decided that with more spring, Id be able to run the front sway on the middle setting instead of full stiff. 1st run, car was stupid loose. I wound up adjusting shock settings to get it settled down by the 3rd or 4th run. Conclusion is that Ive never had this much fun in this car. Afternoon runs were the best its ever handled. Body roll seems to be reduced, even with the softer sway setting.

External video below of some of the even run group in the morning, along with my 1st 3 runs.


thanks for the advice guys.

 

Good to hear! Can't argue with those results.

I always do worse for at least 1 event after making suspension changes for the better. It takes some time to un-learn all of those bad habits I developed to compensate for my old setup.

 

Why are you running -2.5 in the rear? I've never heard of an STU car running much more than -1.5.

 

I plan to run less. But I didn't realize the stu guys ran that low. Is there any reason I should have the shop set it for more than 1.5 or so? Appt on Tue.