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

[cobra]

So 3DM is recommending a 7" spring for the 300 pound rate I want to run in the front. You guys have me worried that it won't get me the travel I need or the recommended height of 13.5.

Anyone have first hand experience with the 7" 300lb spring rate?

What diameter? Barrel or straight wound? You can look up spring specs on the eibach website. They will tell you the travel available before it binds. For example a 2.25" 7" 300lb spring has a travel of 4.32" (https://eibach.com/us/i-409-eibach-coilover-spring.html)

Statically, the front corner sprung weight is 781lbs. With a motion ratio of 0.94 you can estimate that it will compress (781/300)/0.94 or 2.77". This leaves 1.55" left for compression. If your shock has less than that, you're good. If not, it will bind before reaching max compression. I would add a buffer in there of 1/4 to 1/2" because you don't really want to coil bind and this isn't a perfectly exact thing. There will be subtle variations between cars and ride height.

So how do you determine your travel from ride height? It's complicated because part of that travel is in the bump stop. To be perfectly conservative you can consider metal-to-metal travel.

All that said, I am running a 14" ride height and need a 9" spring to not bind. It's okay because it runs inside the wheel. If you run a barrel spring or a 2.5 spring you can run a shorter spring because they have more travel and you might have no choice because otherwise it would rub the tire. There are some options.

[lvm3sm46]

So for the Ohlins, 3DM is recommending a 7" spring for the 300 pound rate I want to run in the front. You guys have me worried that it won't get me the travel I need or the recommended height of 13.5.

Anyone have first hand experience with the 7" 300lb spring rate?

[r4dr]

Where does 10% come from?

I've always heard 10-15% variance is fine before you need a revalve. Not sure if that's just an urban legend.

I went back and looked at my emails. The full story is that Ohlins says up to 20% is fine without a revalve but that will eliminate any potential for adjustment. I'd rather keep the adjustment as that's a big feature of coilovers to begin with.

[Obioban]

Thought it was 25%

That is what Ohlins says.

[lvm3sm46]

Thought it was 25%

[cobra]

I have. He claims you can run 300# springs with the stock valving, but I've talked to someone else who says otherwise. While I trust Barry is familiar with the R&T kit, 300# vs 400# is pretty far out of the 10% (or even 15% if you want to stretch it) rule of thumb for valving.

If you assume you can get away with rates within 10% of the original valving, I could get my fronts valved for 275 and run anything from 250 to 300#.

Where does 10% come from?

[r4dr]

Have you spoken to Barry @ 3DM about that? Im curious his thoughts and he offers the free revalve which you can take at anytime.

I have. He claims you can run 300# springs with the stock valving, but I've talked to someone else who says otherwise. While I trust Barry is familiar with the R&T kit, 300# vs 400# is pretty far out of the 10% (or even 15% if you want to stretch it) rule of thumb for valving.

If you assume you can get away with rates within 10% of the original valving, I could get my fronts valved for 275 and run anything from 250 to 300#.

[lvm3sm46]

Looking back at the R&T setup with lower front rates -- I've confirmed the struts will need a revalve for the struts to run something in the 250-300# range. I'm thinking about having them revalved with 275# as a target, because I should be able to run anything from 250 to 300 for that.

Since it's a 100% street car, I'm going to target something in the 1.16-1.20 range F to R.

Have you spoken to Barry @ 3DM about that? Im curious his thoughts and he offers the free revalve which you can take at anytime.

[r4dr]

Looking back at the R&T setup with lower front rates -- I've confirmed the struts will need a revalve for the struts to run something in the 250-300# range. I'm thinking about having them revalved with 275# as a target, because I should be able to run anything from 250 to 300 for that.

Since it's a 100% street car, I'm going to target something in the 1.16-1.20 range F to R.

[Chas3n]

Ah, true-- the B4s are twin tubes, like the Konis. I assumed you mean the monotube Bilsteins.

Every B4 car I've driven has felt very floaty, but I've never actually tried them paired with flat ride. I could see that addressing the floaty problem.

Paired with the eibach springs and likely just as important, the f/r hotchkis sways, the car feels “good” Also of note I’m on 265/275 tires, low offset wheels. It all comes together, really.

In comparison to what kw v2’s or BC coilovers feel like, this b4/eibach/hotchkis setup feels immensely better in every measurable way.

I’ll reiterate, this is not a track focused setup, but a great GT setup that also works well for a casual HPDE event or even a spirited canyon drive.

Had I decided the m3 was a better hpde chassis than the ap1, I’d have gone down the KW CS w/ flat ride springs, or just paid the piper and done FC’s modified bilstein’s.

[Obioban]

The b4’s ride much better than the koni yellows have. Perhaps you mean b6’s/8?

Ah, true-- the B4s are twin tubes, like the Konis. I assumed you mean the monotube Bilsteins.

Every B4 car I've driven has felt very floaty, but I've never actually tried them paired with flat ride. I could see that addressing the floaty problem.

[Chas3n]

The bilstein dampers ride worse and have worse travel. They're not "better" than the Konis. The do handle better, but they ride worse and are in the bump stops sooner, all else equal.

For a DD, I think the Konis are a better shock. For a weekend car, I think Bilsteins are a better shock.
... which is why my DD M3 (the wagon) and e39 M5 is on Konis and my weekend M3 (the coupe) is on Bilsteins.

The b4’s ride much better than the koni yellows have. Perhaps you mean b6’s/8?

[Obioban]

Mayan was asking and kw or koni. Sure if you open it up there are many more options. I mean... What about stock? When's the last time someone drove a fresh stock setup? It's actually pretty good. Most of us think it sucks because we're just driving old clapped out cars lol

My stock suspension had 1 years and ~10,000 miles when I took it off. It wasn't clapped out. It's not good.

[Obioban]

Why run Koni’s at all? The logical option is to run neither Koni or KW 1/2. Neither damper is ideal, where as either Billy damper is going to be good, depending on if you’re okay with the harsher b8 ride.

The bilstein dampers ride worse and have worse travel. They're not "better" than the Konis. The do handle better, but they ride worse and are in the bump stops sooner, all else equal.

For a DD, I think the Konis are a better shock. For a weekend car, I think Bilsteins are a better shock.
... which is why my DD M3 (the wagon) and e39 M5 is on Konis and my weekend M3 (the coupe) is on Bilsteins.

[cobra]

Why run Koni’s at all? The logical option is to run neither Koni or KW 1/2. Neither damper is ideal, where as either Billy damper is going to be good, depending on if you’re okay with the harsher b8 ride.

Mayan was asking and kw or koni. Sure if you open it up there are many more options. I mean... What about stock? When's the last time someone drove a fresh stock setup? It's actually pretty good. Most of us think it sucks because we're just driving old clapped out cars lol