Coilover spring rates

[greddy]

Copied from evolutionm, I've found that it applies to our cars as well now that I've swapped spring rates because we have the same suspension design in the rear as the evos do. I went from 9/7K to a 09/10K and the rotation is so much better, almost too good with my staggered tires, which means I'll probably go up to a 245 in the rear from my current 235s. Anyway, just thought i would share. Mind you, this is without an upgraded rear sway bar too. The ride hasn't really gotten harsher, I just turned up the dampning a bit and it's still very much daily driveable because my girlfriend, who dislikes riding in my car on shitty streets, said the ride has improved, so hey, I'll take it :)

Quoted from evo M
First, if you don't really care about performance, than it doesn't matter. Get coilovers and get the drop you want. You can close this thread now.

But if you do care about performance, you're doing yourself and your car a disservice by getting the incorrect spring rates.

Second, I'm not going to spell out exactly what are the "best" spring rates. There are so many factors at play. Having a suspension tuner design a suspension for your specific needs and preferences is the best way to go.

This is intended to be a very rough guide people choosing spring rates for coilovers. It is not comprehensive, every car and driver is a little different, I am not a suspension master, and all that stuff.

Crappy spring rates are a problem with several brands of off the shelf coilovers. It does not necessarily mean the coilovers are bad, but the springs should be swapped out if performance is the goal.

Basics

Too stiff. You don't need 14kg spring rates on street tires. You don't have enough grip to generate enough body roll to need super stiff spring rates. You'll likely be overheating your tires. I would recommend R Compounds and stickier when you go past 10kg springs.

This is not a hard rule though and there are exceptions including auto-x, where physics do not really make as much sense (but they are still laws).

Incorrect Spring Rates

What do I mean by incorrect?

Usually when you see spring rates for a set of coilovers it's something like 8kg/6kg. Makes sense, since the EVO is a little front heavy right? Well yes, but there's another factor at play.

The EVO has a multi-link rear suspension. The rear EVO spring is mounted inwards on the arm just a little bit. Unlike the front strut which is pretty much mounted at the hub, a 5k spring rate in the rear does not mean a 5k rate at the wheel. Essentially the suspension arm is a moment arm....placing the spring inwards towards the pivot point means it needs to be stiffer. Sometimes you'll see people mention the "motion ratio." For the front EVO with the strut based suspennsion, it's close to 1 (almost). For the rear, it's somewhere between .6 to .9.

To get the "wheel" rate, you multiply the spring rate by the square of the motion ratio.

So that 8kg/6kg is really more like 8kg/3.7kg ish.

Can you make it work? Kinda. A lot of front camber and a rear swaybar help. But a lot of front camber reduces your contact patch in a straight line and a rear swaybar reduces suspension independence. And then there's the suspension frequency to look at too. So basically yes....you want a slightly stiffer rear spring than the front for the EVO 8 and 9. At the very least, even front and rear spring rates. Top auto-x setups are generally like 12k/16k, but i wouldn't do that for the street or track since that can be a handful.

- Andrew (GTWORX)
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[duh2150]

interesting. good to know info, so do these Evo 8 coil-overs fit the 8g? because i haven't a clue there to get springs with there rates for the 8g lol, I'm in need for a drop again

[blue8g]

^yeah that was i was thinking could i use evo 8 c/o's?

[RedGalant2k1]

No, the mounts are different on the EVO suspension, different chassis. What Martin is getting at is that you can simply order your suspension with a different spring rate than standard. Ksport, Megan, JIC, Tein, and many others allow you to do this with their coilovers.

There are a LOT of other factors in performance also, bound and rebound, ride height, tires, tire pressure, tire tread depth, tire width, etc etc...

[greddy]

Thanks for clarifying man, all I was getting at is that the advertised rear spring rates on a set of coils won't actually be the amount that you get at the rear suspension. and yes there are plenty of other factors that affect performance, I just thought this was an interesting find.

[blkg01]

Does anyone the "degree/angle" that the coilovers mount at the front and rear on the 8G?