Fast road spring rates

[oldroydsr4]

Hi all,

I'm doing the coilover conversion for my daily m50 touring.

I'm aware 600 ft/Ibs for the front and approx 800 ft/Ibs for the rear (standard mounting point) us good for track use,

What is good for a daily with the occasional trackday and driftday.

Cheers

[Jhonno]

350/400 f

600ish r

[oldroydsr4]

What length should I be looking at?

[UweM3]

What length should I be looking at?

The longest one you can get away with.

I know that this is not the answer you expected but there is no general answer. It depends on your rims offset and tyre size.

a rough guess I would say 5-6"

Are you going to run helper springs?

What top mount are you using?

Are you going to convert some OEM struts to coil overs or buying off the shelf?

600lbs rears is meant to go in spring stock location

the green curves is my "old" setup and I think that was fine for street use and not too bad for the Track either. But it's already on the stiffer side IMHO.

[GeoffBob]

Nice Graph Uwe. Illustrates very nicely just how linear the OEM springs actually are! In other words, regardless of displacement, the stiffness of the OEM (front and rear) springs stay reasonably constant (since the slope of the line is constant). I don't like the look of that FS front spring though, which appears to almost double its stiffness after just an inch of displacement. The Eibach front and rear springs also appear very linear, the rear just a little softer than the OEM.

From that graph then, the OEM front springs are roughly 100lbs/inch and the OEM rears are 300lbs/inch? Interesting to note that the only spring there that is stiffer than OEM on the rear is the KW, which is also quite non-linear. Are the rear springs listed on that graph all located in the stock position (apples with apples and all that)?

[UweM3]

The KW rear is a little bit progressive, guess this happens when the large coils start binding and is meant to be like that.
The FS front spring is a dual rate spring and was deliberately wound like that. Makes for a smooth ride while poodling along but stiffens up when giving it some beans. A linear spring rate would have resulted in a very short spring becoming loose on full droop.

What surprised me was the graph of the Eibach "progessive" lowering spring kit! Basically they just use M3 OEM spring rates and shorten them a little bit to lower the car.
I didn't even fit them (they are for E30 four cylinders BTW)

The graphs are from a spring Dyno, not measured on the car. But all for the stock spring position.

The KW rear and FS front together with some Bilstein shocks are actually quite a good setup.
Still good for the road but very neutral on track and good for some decent laptimes. But too soft
if you want to go really fast on track

[AlpineAde]

The Eibachs surprise me, too. Mine are 143 lb/in front and 274-377 lb/in rear, which is stiffer than OEM for the 325i.

[UweM3]

The Eibachs surprise me, too. Mine are 143 lb/in front and 274-377 lb/in rear, which is stiffer than OEM for the 325i.

yours are 325 springs and NOT 4-cylinder springs.
Somebody also pointed out that the stock M3 front spring has the same P/N than a 318 spring!

[AlpineAde]

I realize that. I was just highlighting the strangeness of the oddly "standard or softer" Eibach springs you mentioned in relation to the 4 cylinder cars. It's definitely not something that is carried through the Eibach range as a "design principle".

[UweM3]

I realize that. I was just highlighting the strangeness of the oddly "standard or softer" Eibach springs you mentioned in relation to the 4 cylinder cars. It's definitely not something that is carried through the Eibach range as a "design principle".

I wasn't implying anything like that. Just talking about E30 M3 springs. Eibach doesn't make any springs specific for the M3 and everybody is using the 4 cylinder springs. After having the eibach springs measured I was wondering if it wouldn't be better to use the 6cylinder springs. The slightly harder fronts would be a benefit in terms of handling IMHO.
but I required something stiffer and went with the "green" combination of springs

[oldroydsr4]

Uwe,

my plan is to copy the ground control kit where possible so the plan is to..

1. Convert my struts using gaz treaded tube
2. Standard rear perches with adjustible platforms.
3. No helper springs
4. Standard top mounts.
5. After a bit of research the GC kit uses 6" fr springs at 325Ibs/inch and 5.5" rr springs at 450Ibs/inch

what's your thoughts on the above?

[UweM3]

Uwe,

my plan is to copy the ground control kit where possible so the plan is to..

1. Convert my struts using gaz treaded tube
2. Standard rear perches with adjustible platforms.
3. No helper springs
4. Standard top mounts.
5. After a bit of research the GC kit uses 6" fr springs at 325Ibs/inch and 5.5" rr springs at 450Ibs/inch

what's your thoughts on the above?

1. I used GAZ, very good kit and price. (hint: get the threaded tubes zinc plated BEFORE you weld them on the strut. Mine still look perfect)
2. which platforms are you going to use? Keep in mind the lower platform doesn't exist if you remove the rubber bumpstop
3. Why?
4. Why? (you loose suspension travel with standard mounts)
5. 6" front is a good length, but with 325lbs you need to keep an eye on shock travel 450lbs rear seems a bit low to me.
Keep in mind that GC is cutting 1" of the strut and uses Corrado shocks to gain some travel.

6. What shocks are you going to use?

[Jhonno]

450 is low imo.. I liked the 580 rear with 350 front and that was with a saloon! Your Touring will need more rear spring rate..

[AlpineAde]

I wasn't implying anything like that.

I know you weren't, Uwe.

[vladv]

Guys, are you talking about springs at standard place without rear coilover unit.
I choose GAZ fr 500lbs and rr 375lbs for drifting all are coilovers units. Hope it will be Ok! for first time riding.

[oldroydsr4]

3. Why?

I know it sounds a little pikey but really due to cost, the plan was to have a budget coilover kit for fast road, do you think helper springs are a must? I dont plan on getting huge air.

4. Why? (you loose suspension travel with standard mounts)

This is also a cost related point, or can you recommend some good top mounts at a reasonable price?

5. I'm using Kw dampers.

[UweM3]

3. Why?

I know it sounds a little pikey but really due to cost, the plan was to have a budget coilover kit for fast road, do you think helper springs are a must? I dont plan on getting huge air.

4. Why? (you loose suspension travel with standard mounts)

This is also a cost related point, or can you recommend some good top mounts at a reasonable price?

5. I'm using Kw dampers.

I don't think it will be super critical in your application to have helper springs. And as you are clued up, you will make sure the springs are properly seated after you jacked you car up.

If I wouldn't be so busy and finally find some time to make some more top mounts you could run some of mine. Jhonno is running them for 1 year+ with no issues (solid mounts that is)

[randomspeedfreak]

3. Why?

I know it sounds a little pikey but really due to cost, the plan was to have a budget coilover kit for fast road, do you think helper springs are a must? I dont plan on getting huge air.

4. Why? (you loose suspension travel with standard mounts)

This is also a cost related point, or can you recommend some good top mounts at a reasonable price?

5. I'm using Kw dampers.

I don't think it will be super critical in your application to have helper springs. And as you are clued up, you will make sure the springs are properly seated after you jacked you car up.

If I wouldn't be so busy and finally find some time to make some more top mounts you could run some of mine. Jhonno is running them for 1 year+ with no issues (solid mounts that is)

im thinking of doing exactly the same so this thread has been really useful so far as im also on a budget

Uwe what do your topmounts look like? how do they get more spring travel over standard?

[UweM3]

3. Why?

I know it sounds a little pikey but really due to cost, the plan was to have a budget coilover kit for fast road, do you think helper springs are a must? I dont plan on getting huge air.

4. Why? (you loose suspension travel with standard mounts)

This is also a cost related point, or can you recommend some good top mounts at a reasonable price?

5. I'm using Kw dampers.

I don't think it will be super critical in your application to have helper springs. And as you are clued up, you will make sure the springs are properly seated after you jacked you car up.

If I wouldn't be so busy and finally find some time to make some more top mounts you could run some of mine. Jhonno is running them for 1 year+ with no issues (solid mounts that is)

im thinking of doing exactly the same so this thread has been really useful so far as im also on a budget

Uwe what do your topmounts look like? how do they get more spring travel over standard?

trade secret can't tell you.
the top mounts do not give you MORE spring travel, they don't take any spring travel AWAY. The flatter the top mount, the lower the car is to start with. This will enable you to wind the coil over further up which pulls the shock rod further out of the shocks body giving you more travel. Does this make sense???

[oldroydsr4]

When are going to make some more?

Or can you recommend some?