I'd like to lower it, but I don't want to increase stiffness.

[Blau]

what springs are my city folk using? car is used 100% in the city and has my kids in it daily. can't go any stiffer. I want to look good and be low, but I'm not about that bounce life.

any recs greatly appreciated. stock 128i

[tracer bullet]

Generally speaking these things go together. Lower means shorter springs, shorter springs need to be stiffer so you don't bottom out all over the place. Shocks are stiffer accordingly to handle the stiffer springs, otherwise you bounce. The don't guarantee a bad ride exactly, there are a lot of factors, but again generally this is how it works.

[ShocknAwe]

If you don't want a harsher ride my opinion is you'll have to spend big $$ overhauling everything including nonRFT, bushings, arms, and coilovers with more technically advanced internals.

There is no cheap way to do it.

[Edrift]

Easy. If you want lower and not stiffer you can just cut the springs.

That way it retains the same spring rate but sits lower.

If course this isn't recommended because you will bottom out if you go too low and drive on rough roads.

[tracer bullet]

Originally Posted by Edrift

That way it retains the same spring rate but sits lower.

Actually, part of the spring rate formula involves the length of the spring itself (the length of the spring if you were to unwind it and stretch it out). A shorter spring, all else being equal, gives a higher spring rate.

[ShocknAwe]

Originally Posted by Edrift

Easy ... just cut the springs.

And there it is. Figured it was only a matter of time.

[b1aze]

Originally Posted by ShocknAwe

And there it is. Figured it was only a matter of time.

Combine this with the recent influx of “I don’t wanna do my own research, spoon feed it to me on demand” and we’ve officially dipped into Honda-forums territory.

[Edrift]

Originally Posted by tracer bullet

Actually, part of the spring rate formula involves the length of the spring itself (the length of the spring if you were to unwind it and stretch it out). A shorter spring, all else being equal, gives a higher spring rate.

From memory the formula involves counting coils too. So no it wouldn't be stiffer, same softness just shorter.

In any case the OPs question is nonsensical and deserves the cutting coils answer.

Lower cars require stiffer springs to operate correctly... Even then there is a limit to how low and stiff you can go....

[John_01]

If you go lower, you really need to use stiffer springs. There isn't any good alternative with the E82 BMW. The car doesn't have much ground clearance and not much suspension travel. So if you lower with springs that are too soft, the car will ride badly because of hitting the bump stops continuously. The stock suspension already has that problem with the bump-stops, except at lower height it will become much worse.

[ShocknAwe]

So theres a bit of a misconception on this forum and elsewhere about the bump stops. I myself had this issue and had it explained to me by a suspension engineer recently. As I am NOT an engineer, take this with a bit of a grain of salt as its now the deaf dumb and blind kid relaying info...

The bump stops are an integral internal spring for the standard E82/E9x suspension. At ride height, the car effectively rides on the upper part of the bump stop on the stock suspension. They are not there only to protect the dampers from bottoming out

With lower kits and matching dampers, this is less so, but the stops are engaged progressively with any quality kit.

Thus the way the stops are shaped, with increasing stiffness the more they are engaged.

THE PROBLEM:
The stock dampers are undervalved and the stock spring rates are already soft. This is matched to overly stiff non-RF tires. The dampers continuously bottom out regardless of design.

THE FIX:
Slightly increase spring rate to better match body weight of the car, add properly valved dampers with appropriate stroke length for bump and droop. Remove overdesigned compliance in rear subframe and small number of points in front and rear suspension as outlined by fe1rx. Replace nRFT with proper A/S or Summer tires.

[tracer bullet]

Originally Posted by Edrift

From memory the formula involves counting coils too. So no it wouldn't be stiffer, same softness just shorter.

It does, as well as diameter of the spring itself, # of active coils, things like that. But it's part of a calculation that ultimately arrives at the length of the spring if you were to unwind it into a straight rod as I mentioned.

Basic math says if you change a number plugged into the equation (i.e. # of coils), you have therefore changed the rate that is calculated.

[Blau]

didn't mean to cause drama.. I've learned a good amount anyway. So, in short, what I want to do is not possible, really. Any lowering will be accompanied by interested stiffness.

thanks!

[asbrr]

Originally Posted by WeShallCallHerBlau

didn't mean to cause drama.. I've learned a good amount anyway. So, in short, what I want to do is not possible, really. Any lowering will be accompanied by interested stiffness.

thanks!

Generally yes, but there are options out there that would give you a decent ride in "many" situations (not all) and lower the car. If you have the money, the updated E82 specific Ohlins Coilovers are a good example. They are height adjustable so you can lower the car a bit while leaving enough suspension travel (I wouldn't lower it to the lowest setting for example), and because of their sophisticated damper design will ride surprisingly well. You'll probably get a reasonably smooth ride on small/sharp bumps, but make no mistake you hit a big bump the car will get back under control quickly and not "float" like the stock suspension.

That means you're going to feel the suspension arresting the car's momentum quickly = can feel harsh/stiff.

How a car rides is a very subjective thing, and means different things to different people.

[HP Autosport]

Originally Posted by WeShallCallHerBlau

what springs are my city folk using? car is used 100% in the city and has my kids in it daily. can't go any stiffer. I want to look good and be low, but I'm not about that bounce life.

any recs greatly appreciated. stock 128i

Low and not stiff? I don't know that can happen on stock dampers. Your best bet is coilovers with spring rate options.

[lab_rat]

Originally Posted by ShocknAwe

So theres a bit of a misconception on this forum and elsewhere about the bump stops. I myself had this issue and had it explained to me by a suspension engineer recently. As I am NOT an engineer, take this with a bit of a grain of salt as its now the deaf dumb and blind kid relaying info...

The bump stops are an integral internal spring for the standard E82/E9x suspension. At ride height, the car effectively rides on the upper part of the bump stop on the stock suspension. They are not there only to protect the dampers from bottoming out

With lower kits and matching dampers, this is less so, but the stops are engaged progressively with any quality kit.

Thus the way the stops are shaped, with increasing stiffness the more they are engaged.

THE PROBLEM:
The stock dampers are undervalved and the stock spring rates are already soft. This is matched to overly stiff non-RF tires. The dampers continuously bottom out regardless of design.

THE FIX:
Slightly increase spring rate to better match body weight of the car, add properly valved dampers with appropriate stroke length for bump and droop. Remove overdesigned compliance in rear subframe and small number of points in front and rear suspension as outlined by fe1rx. Replace nRFT with proper A/S or Summer tires.

The best "Cliff Notes for E8/E9x suspension" I've read yet.

[HP Autosport]

The bump springs have been used in the racing world for a while now.

Swift now offers bump springs that are much more progressive or linear(depends on the setup and what you are trying to achieve) than the foam rubber secondary springs. Using the bump spring one can have a very compliant rate during the initial stroke of the suspension and a different rate at dynamic ride heights. Foam rubber also changes rate according to temperature and wears out quicker than bump springs.

[Driven5]

Originally Posted by tracer bullet

It does, as well as diameter of the spring itself, # of active coils, things like that. But it's part of a calculation that ultimately arrives at the length of the spring if you were to unwind it into a straight rod as I mentioned.

Basic math says if you change a number plugged into the equation (i.e. # of coils), you have therefore changed the rate that is calculated.

Neither of you is totally right, and neither is totally wrong.

The equation for the rate of a coil spring is:
k = (G * d^4) / (8 * n * D^3)
k=spring rate
G = Modulus of elasticity (generally constant)
d = spring wire diameter
n = number of active coils
D = spring coil diameter

Notice there is no accounting for overall length of the spring, and therefore the length of the spring has no effect on the rate itself. However, cutting a coil reduces the number of active coils, and that does increase the spring rate in addition to shortening the spring.

If you understand the physics behind it, cutting coils can be done in a perfectly functional way...The reason it gets a bad rap is that few people understand how it works and what its fundamental limitations are to be able to do it the 'right' way.

[Driven5]

Originally Posted by WeShallCallHerBlau

car is used 100% in the city and has my kids in it daily. can't go any stiffer.

Going stiffer does not have to mean going dramatically stiffer, as long as it's not dramatically lower...Nor does it inherently mean poor ride quality either.

Going from Base to MSport is a little lower and a little stiffer, but most enthusiasts actually find that to be an improvement. Eibach Pro-Kit springs are another small step lower, and another small step stiffer...But consider that they aren't even any stiffer than E9X MSport springs are claimed to be.

Within the relatively mild rate differences we're talking about, things like damper stiffness, having enough (matched) spring/damper resistance to not crash into the bumpstops, and even getting rid of the too-stiff rates in the factory spec (run-flat) air-springs on your wheels all actually have a greater effect on ride harshness and the 'the bounce life' than spring rate alone does.

[tracer bullet]

Originally Posted by Driven5

Neither of you is totally right, and neither is totally wrong.

The equation for the rate of a coil spring is:
k = (G * d^4) / (8 * n * D^3)
k=spring rate
G = Modulus of elasticity (generally constant)
d = spring wire diameter
n = number of active coils
D = spring coil diameter

Notice there is no accounting for overall length of the spring, and therefore the length of the spring has no effect on the rate itself. However, cutting a coil reduces the number of active coils, and that does increase the spring rate in addition to shortening the spring.

If you understand the physics behind it, cutting coils can be done in a perfectly functional way...The reason it gets a bad rap is that few people understand how it works and what its fundamental limitations are to be able to do it the 'right' way.

I think you misunderstood my post. Notice that I said the length meaning the length of the rod which would result if you were to unwind the spring. You can see in your calculation about the # of active coils and the diameter of the spring - those things become the length of the spring if you were to unwind it and turn it into a rod. I'm not talking spring height i.e. how tall it would be if it were sitting on the garage floor after being removed. I think you took my "length" word and misunderstood it for "height".

A spring is a coiled up rod of chrome-vanadium steel. Rate is related to the properties of that rod, namely the material, the diameter of the rod, and the length of the rod. In other words, how hard it is to twist that rod if you were to grab each end.

That's an oversimplification of course, some springs have different diameters from one end to the other, coils that are not active, and so on. But it gives you an idea of how they work.

Cutting a coil shortens that rod and actually makes it harder to twist the same amount if it were longer. AKA the spring rate changes.

[Driven5]

Originally Posted by tracer bullet

I think you misunderstood my post.

My apologies. I caught that reference and meaning in your second reply to Edrift, but somehow misinterpreted it in your first reply. Rereading it, I'm not sure how though.

I too have always found it useful to think of coils springs as little more than fancy torsion springs.

[tracer bullet]

Originally Posted by Driven5

My apologies. I caught that reference and meaning in your second reply to Edrift, but somehow misinterpreted it in your first reply. Rereading it, I'm not sure how though.

I too have always found it useful to think of coils springs as little more than fancy torsion springs.

The torsion spring is a good comparison as well. Hmm, now you have me wondering which is the better comparison! Have to think about that a bit.

[Driven5]

Let me fix that:

"I too have always found it useful to think of coils springs as little more than fancy torsion bars."

We're saying the same thing.