Bee-Raddd

This is exactly what i want to hear. i suspected there was something to do with the mac strut up front but not in the rear etc. i see dallas touched on it in the suspension thread but i never found a complete answer from anybody.

I just read through this entire thread https://www.evolutionm.net/forums/ev...ur-evo-24.html
now my head hurts.


So what im thinking i might do going forward is swap the springs front to rear so 14kg front 16kg rear.

Ill ditch the 20mm rake i was told to add recently as i think thats just made the lifting worse and put it back to level front to rear.

Does anybody have a ballpark ride height that works? i was always told to keep the A arm level in to outside at a minimum when lowering the car. i have heaps more room to go lower in the guards and the aero kit would love it. but how low can u go really?

Also with swapping the spring rates round should i bother installing the stiffer FSB ? I have stock size whiteline rear bar which i can adjust. its on full hard at the moment. might be worth softening that up a bit?

But yea do i put the bigger bar up front or leave it out is the big question

Bee-Raddd

one thing that does worry me tho is swapping the 14kg spring to the front isnt that just going to make the rear wheel pick up even more and the front dive more? or am i missing something?

LetsGetThisDone

iTrader: (1)

Measuring the pinch weld, my car is 3/4" lower in the front than the rear. In the rear, the lower control arm the shock mounts to points up just a little bit to the tire. I don't remember ride height though.

Dallas J

iTrader: (1)

Here we like to start with the math, then adjust with our butts

The motion ratio is slightly variable, but the calculation for natural frequency (a relatively easy way to compare the stiffness of a system) takes into account both the weight and the motion ratio. The interesting thing is that the MR^2 (you square for freq calcs, but not for displacement or force calcs) is that the Front rear ratio ends up being close to ratio of front/rear weight.

MR^2 = 0.96^2 / .72^2 = 1.78

Weight = ~1000/600 = 1.67

So if you just look at natural frequency, you should end up running a little bit more in the rear if you subscribe to the notion rear NF should be slightly above front.

Things change a bit once you also add in the effects of tire spring rate which happen outside of the suspension MR. This will reduce your NF of each end but more so up front where the weight is almost 50% higher. Looking some of my old numbers I have in a spread sheet, if I had 700/700 spring rates and tires at 3000lb/in then,

Without tire consideration, NF = 2.85 front / 2.73 rear
With tire consideration, NF = 2.58 front / 2.64 rear

And the softer the tire, the greater the split grows. Caveat though, its hard to predict tire rates. Pressure, wheel width, tire width, brand, age, camber, etc. all can play a role. And they probably aren't even close to linear. I just guess 2000 for top tier street tires and 3000 for top race tires.

Stepping beyond just NF, Front roll center drops at a rate 3 times faster than the rear by the nature of Mac Strut vs Multi link suspension. That lower roll center is going to cause the outside tire to dive on sort of an anti-jacking force effect. So now you have a wobbly table where if one side drops down the cross corner must lift. The solution to this is to raise front RC via front ride height or geometry, or increase front rate. Though you've found the later to still not be enough. A simple thing you could try, just raise the front of the car 1" for an event.

kaj

iTrader: (60)

Without having any adjustments made to roll center, bump steer, etc. I've lowered my car to the point where components are slightly above level. It doesn't look as nice as other cars, but it works LOL. I also run exactly 13mm of rake; I really like the effect that had on the car. It drives super nice and is very neutral.
At some point, I'd like to get a set of uprights from Dallas so I'm not limited on ride height.
I think most of us are on stock FSBs and aftermarket rear... though I do remember reading threads on here where people swear by upping the front. Hopefully someone who knows best can chime in.

Ayoustin

iTrader: (2)

I haven't looked much into the evo but I used to own a BMW 135i and those guys swear by larger front sway bars to reduce understeer and increase roll stiffness and that car has a similar ish suspension to an evo (mac struts in the front and a multilink in the rear).

IMO the big piece of the puzzle is the fact that we have mac struts in the front and mac struts have pretty bad camber curves. Reducing camber in roll can be done by increasing roll stiffness and chassis stiffness. Increasing sway bar rates increases roll stiffness, and adding things like chassis braces increases chassis stiffness. On certain platforms I've seen bigger FSBs help reduce understeer (mostly RWD platforms) and on other platforms I've seen chassis bracing like strut braces and LCA tie bars increase chassis stiffness (mostly FWD platforms).

kaj

iTrader: (60)

Our cars don't work like any of those ,though.

DaWorstPlaya

iTrader: (31)

On a stock suspension Evo, if you put a larger front sway bar it actually oversteers. With coilovers and stiffer springs, it starts to follow the "normal" tuning guidelines.

Wanted EVO IX

I've spent the last two years with my Evo autocrossing and searched the forum about this topic and several people here have given out ideas and suggestions on the 3 wheel motion we struggle with. I've seen others with Evos at our local region not 3 wheeling. I asked them about what setup they are running for suspension and found out that the other Evos have a longer rear coil spring setup than I do. My car has 6'' springs on all four corners and they have 6" Front and 7" Rear. I do have a set of 7'' Rear springs at home but they are 10K and I currently have 12k in the rear. This might help you guys out and I would consider doing the same myself.

Ayoustin

iTrader: (2)

IMO suspension type and weight distribution trump drivetrain layout in this scenario. We definitely don't have as desirable weight distribution as those cars, which actually plays in favor of running a stiffer FSB since more weight on the front axle would result in greater roll in the front and a stiffer bar would be beneficial.

There's definitely no question that front grip is much harder to increase than rear grip.

MinusPrevious

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After all this time, I feel, there is a general consensus among the hard hitting track guys

In layman's terms (only language i speak)
Big sways & Big springs dont work well together (its one or the other)

Most of our expert track Gurus run the stock FSB & high rate springs. Too much rate up front (high rate FSB coupled w/high rate springs) = Wicked understeer & inside front tire lift in corners

kaj

iTrader: (60)

That sums it up really well, though there are still those that swear it can't be right and their setup is better. That really makes me wonder. All the competitive cars I've seen on the road course run exactly what you describe (They are running typical Evo running gear; nothing exotic). Not sure about lifting the front tire, though (I haven't heard/read, not saying it's not true).

Ayoustin

iTrader: (2)

I've got WL bars on both ends and the car felt pretty neutral to me on the track last year, we'll see if that still holds true this year after the changes I've made. I'm already registered for 4 days at Gingerman in April and May so by the end of May I should have a pretty good feel for where the car is and hopefully get anything I'm not happy with sorted by then as well.

MinusPrevious

iTrader: (3)

Thanks Jason. That statement was based off my personal interview w/John Mueller some years ago.
Mueller had attempted many diff spring rate & FSB combinations but could not keep the inside tire on the ground on low to mid speed tight corners.
He realized through experimentation that too much FSB rate increased the already prone understeer tendency coupled w/tire lift (AWD performance killer)

Just in the last few weeks we had an experienced track EvOM member who just removed his uprated FSB to stock. Cant recall who that was off hand

EVO8LTW

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