e46 M3 suspension setup, or how to not downgrade your car with suspension mods

[cobra]

Can you clarify what you mean by "shock tunes"?

Is this any help:

Planning to raise the car some and figured I'd throw in some springs while at it before getting it re-aligned. I actually don't mind the the current rates but am intrigued by this flat ride thing ahah

Exactly, shock tunes referring to the force-velocity and force-displacement curves of the shocks.

That is a force-displacement curve. I would also need to see at what speeds those lines correlate to, and seeing a force-velocity curve would also be helpful.

What I can gather from that graph is that assuming it's a single adjustable shock, the adjuster affects both compression and rebound. The reason it affects compression so much less is because it's a much softer shim stack. It also looks like it has a heavily preloaded compression stack, which is not conducive to comfort because it requires so much force just to get the shock moving. The rebound/compression ratio ranges from 0.6 at "low" speed to 1.7 at "high" speed which is low for a street car. My takeaway is this tune is designed for someone who wants a very responsive handling car that doesn't care so much about comfort and drives primarily on smooth roads.

[kaiv]

It's impossible to advise on the complete picture without knowing your shock tunes.
I would be running a 400 or 425 front springs to match those 670 rears, if you're happy with those.

You don't have much room to lower the front before relying on the bump stops, which will further increase the spring rate. Try taking a look to see how close you are to the bumper at static height.

Careful going too low on spring rate because you might run out of spring travel, and might need to run a much longer spring.

Can you clarify what you mean by "shock tunes"?

Is this any help:

Planning to raise the car some and figured I'd throw in some springs while at it before getting it re-aligned. I actually don't mind the the current rates but am intrigued by this flat ride thing ahah

[cobra]

I was surprised when years and years ago, even on the old forum, that there was no information concerning spring length, travel, etc. I think tbone is pretty dead on in his estimates.

A 9" spring, man, that I wouldn't have guessed.

I made a calculator that lets you input your spring properties and ride height and tells you what spring length you need. I will tidy it up and upload it here!

edit: I ran into some difficulties in the rear since the shock travel and spring travel are different, so it needs to work slightly different. Will hopefully get it shared soon.

[oceansize]

I was surprised when years and years ago, even on the old forum, that there was no information concerning spring length, travel, etc. I think tbone is pretty dead on in his estimates.

A 9" spring, man, that I wouldn't have guessed.

[cobra]

True true

Maybe others can share their experience, and we can get a fairly accurate guide.

Other issue the position of the bottom perch relative to the strut's height from strut to strut. MCS have tons of range, but others, like GC street kit, don't have as much. That'll result in some issues like when you're at that 350-400 range and you'd like to run a 7" (no 6.5" exists sadly, tck vvs come close at 6.25"), but a 7" won't let you get down to 13.5" so you have to choose.

There are some barrel style (like eibach XTs) springs that will give a little more travel. I had a set (2.5") in 400lb and they did the trick, but ultimately went with TCK 6.25" 400lb since I went to 60mm perches. 6" is too short for 400lb imo, it's really close.

I had to run a 9" 300lb spring at stock height and even then it almost coil binds at bottom-out (metal to metal).
If you lower the car you can run a shorter spring since there is less travel requirement.

[Tbonem3]

True true

Maybe others can share their experience, and we can get a fairly accurate guide.

Other issue the position of the bottom perch relative to the strut's height from strut to strut. MCS have tons of range, but others, like GC street kit, don't have as much. That'll result in some issues like when you're at that 350-400 range and you'd like to run a 7" (no 6.5" exists sadly, tck vvs come close at 6.25"), but a 7" won't let you get down to 13.5" so you have to choose.

There are some barrel style (like eibach XTs) springs that will give a little more travel. I had a set (2.5") in 400lb and they did the trick, but ultimately went with TCK 6.25" 400lb since I went to 60mm perches. 6" is too short for 400lb imo, it's really close.

[SQ13]

Yes IMO, roughly: below 300lbs, 8" 300-400lb - 7" 450-650lb - 6" 650lb+ - 5.5"-5"

Sir, this is formatted very poorly 😂

below 300lbs - 8"
300-400lb - 7"
450-650lb - 6"
650lb+ - 5.5"-5"

[Tbonem3]

There's a likely need to change spring lengths as well, right?

Yes IMO, roughly: below 300lbs, 8" 300-400lb - 7" 450-650lb - 6" 650lb+ - 5.5"-5"

[cobra]

Hey guys,

I have a car that I got pre-modded that I'd like to dial in more to my liking.

As is the handling is a bit interesting to say the least. The rear end has almost incredible traction and tractability out of a turn however the front end gives up much too early. It's not balanced. The car is also much too low.

What I want/like: a strong front end and oversteer tendencies if I overcook it. Not sure if that qualifies as neutral-ish.


Hardware:

JRZ RS One
Swift springs 100F (+ helper) / 120R (+ tender rate unknown)
H&R sway bars (F soft, R stiff)
GC adjustable end links

Rates translate to ~558lb and ~670lb

Would dropping the front spring to 6kg (~335lb) be a good move?

It's impossible to advise on the complete picture without knowing your shock tunes.
I would be running a 400 or 425 front springs to match those 670 rears, if you're happy with those.

You don't have much room to lower the front before relying on the bump stops, which will further increase the spring rate. Try taking a look to see how close you are to the bumper at static height.

Careful going too low on spring rate because you might run out of spring travel, and might need to run a much longer spring.

[zzyzx85]

I'm going to have my JRZ RS Ones sent out for rebuilding as well so this has crossed my mind. Currently 450lb/550lb. per the calculator, i should be going to 300lb front if i leave it at 550 rear. There's a likely need to change spring lengths as well, right?

[Cronenberged]

kaiv yes dropping the front rate and doing stiff front and soft rear sway bars.

[K-Dawg]

Would dropping the front spring to 6kg (~335lb) be a good move?

I think so. I'm not too familiar with the JRZs, but bump stops are stiff springs, so if you're on the bump stops, your front spring rate is effectively higher and will contribute to understeer.

Maybe you also have something else going on like worn components, bad alignment or crap tires.

[kaiv]

Hey guys,

I have a car that I got pre-modded that I'd like to dial in more to my liking.

As is the handling is a bit interesting to say the least. The rear end has almost incredible traction and tractability out of a turn however the front end gives up much too early. It's not balanced. The car is also much too low.

What I want/like: a strong front end and oversteer tendencies if I overcook it. Not sure if that qualifies as neutral-ish.


Hardware:

JRZ RS One
Swift springs 100F (+ helper) / 120R (+ tender rate unknown)
H&R sway bars (F soft, R stiff)
GC adjustable end links

Rates translate to ~558lb and ~670lb

Would dropping the front spring to 6kg (~335lb) be a good move?

[r4dr]

my consumer V3's just went in for a rebuild last week and I just got the call today that they don't want to rebuild them as they're slammed with race builds for the start of season, instead they're sending a new dampers from Germany.

I never felt the V3's were stiff, always thought they were extremely compliant even on Houston streets.

To SQ13's chagrin, I may just run them with some linear springs and see how they do 😘


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I've heard good things about running proper linear springs with the V3s. The impression I got was that the V1/V2 is not worth messing around with, but the V3s are competent in the damping department.

I don't remember the spring rates that the people were using, but I'm sure you can find it via Google. It was Harold @ HPA who was talking about this.

[fattycharged]

What can I say, I'm a glutton for punishment…


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