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

[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.

[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"

[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]

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.

[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.

[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]

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.

[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]

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.

[cobra]

Can someone see if the attached excel works for them, and check my math?

I tried it on my car and it got me within 1/4" of the numbers I measured. Maybe there is something wrong with the motion ratio stuff but it at least gives you an idea...


It lets you input spring parameters, vehicle weight, and shock travel, and lets you know how close you are to coil bind at bottom-out. I also included every spring Eibach makes which is going to be reasonably close to other manufacturers of 2.25/60/2.5 springs.

[Drewrivera]

Anyone know if alpina set ups work for M.? Was it just springs or did it have a whole set of different dampers? 😶😶

[Driver407]

duracellttu
Been reading and learning about flat ride all weekend. Just finished all 25 pages here among others.
You seem to have gone down a very similar path and asked the same questions I have had going through all of it.

Bought a set of TCK D/A with 400/500 as recommended by Mr. Kline. Is a dedicated track car that sees some backup-daily usage. 3350lb no driver. 50% corner balanced. Looking into flat ride info and had a few questions about your journey.

I see you went down the path of TCK S/A with ~350 and ~700. Said it was pretty bumpy? Did some adjustments and didn't really hear if it helped? Think you even debated getting D/A rears it seems.
You also inquired about why TCK recommended the 400/500 to you (My setup). Without much further forum discussion. Just trying to see what angle he has vs the flat ride mentality. If you ever maybe discussed that elsewhere.

Curious where you landed after all this time. Did you get the original 350/700 setup to work?
Did you end up happy with the outcome after doing flat ride on the tck?

Just looking for some tips. Literally just did my corner balance and yearly alignment last month. Kinda wish I had learned all this before that! lol. My car has felt great the last few track days but now this has me intrigued.

[Bry5on]

I've been detailing a bunch of suspension geometry modeling work in my build thread here - it's ready enough to share with folks here if you're interested in really getting your suspension right. If you're lowering the car, especially if you're lowering the front, it's easy to mess the balance up.

Simplified CAD model of the e46 M3 suspension: https://cad.onshape.com/documents/a1...66f543dbff2801

CG and roll modeling in attached excel ( CG location change_332it.xlsx ):


As well as modeling suspension curves for different height settings:

[Obioban]

I've been detailing a bunch of suspension geometry modeling work in my build thread here - it's ready enough to share with folks here if you're interested in really getting your suspension right. If you're lowering the car, especially if you're lowering the front, it's easy to mess the balance up.

Simplified CAD model of the e46 M3 suspension: https://cad.onshape.com/documents/a1...66f543dbff2801

CG and roll modeling in attached excel (CG location change_332it.xlsx):


As well as modeling suspension curves for different height settings:

Awesome!

[STAATS]

I've been detailing a bunch of suspension geometry modeling work in my build thread here - it's ready enough to share with folks here if you're interested in really getting your suspension right. If you're lowering the car, especially if you're lowering the front, it's easy to mess the balance up.

Simplified CAD model of the e46 M3 suspension: https://cad.onshape.com/documents/a1...66f543dbff2801

CG and roll modeling in attached excel (CG location change_332it.xlsx):


As well as modeling suspension curves for different height settings:

Awesome!
Although I can't find a link to the excel sheet?
Also thanks for the link on onshape that's a pretty cool service being that its free for hobbyists, may be a better location for me to house the random E46 M3 related CAD models I have collected over time than on Google Drive for sharing