M325i vs SR20DET.

[CamB 48]

Further comment - am still not sure why you're worried about preload (within reason) - an E30 has plenty of both with standard springs.

[E30-323ti 66]

Ahh yes indeed I must be, didnt realise they were different shot for clearing that up. So you would need different length springs like Henry was saying to get the right height?

No worries.

No, It doesn't matter what the spring length is, as the rate is still the same.

The amount of preload applied to the spring determines the ride height.

Say you have 400# springs & the front of the car is 800# each side will compress 1" from the free length (if the springs are captive).

Now preload each side with 200# (1/2" up on the collars), now the effective starting load is 600# when you put 800# of car on it, you compress the springs 1/2" each side, resulting in a higher ride height.

The "lowest" a given setup will ever go is when the spring has no preload at the shocks free length.

If henry is saying that free length is too short, ie the car will always be too low no matter how much preload he uses, then yes, the shocks are too short.

If on the other hand, he can't get it low enough because with the spring at no preload does not sag enough when loaded, then you need to use tender springs (lower rate) to take up the desired sag and remain captive (have a look at some of the pics of my rear coilovers floating around).

That all looks rather wordy I must say, but pretty easy once you get your head around it.

[|ncary 0]

I can't just wind it up... All that does is squeeze the spring, not change the height, it is all bolted together and I've played with it all day, so I'm not guessing here Need the height adjustment! Otherwise I would have just bought springs haha.

*I see what you mean about the preload changing the ride height, I'd rather not do it that way, would rather have minimal preload and all adustment via the distance the collar travels

Edited June 23, 2009 by Incary

[E30-323ti 66]

The shock stanchion doesn't extend far enough out of the shock housing. Therefore the max ride height is limited by this because the spring is 2 inches longer than GC spec, and clearly they have given me shocks for 6 inch long springs. I'm still going to have the max ride height that 6 inch springs give, but I'm only able to lower it about 1cm, I could get the new spring perch welded on about 5cm lower to get the full range of height adjustment, but that defeats the purpose, it'd be much to low.. I wanted longer springs for long travel, but I still have the same travel as 6 inch springs, and hardly any height adjustability. If I just wind the collar up I'll get massive preload on the spring, and a harsher ride.

The only option really is getting the shocks un-shortened. I assume this can be done. I hope.

Well there is your problem, long springs don't mean longer travel!!!

If the stanchion doesn't extend far enough and you say you can only lower it 1cm, that doesn't add up!!

What are you trying to do, fully extended it's too short, lowered fully it's not low enough????

Sounds like you might need to do suspension 101 !?!?!

The issue with the GC stuff is, the standard spec spring lengths they use 6" front & 5" rear are not captive at most operating ride heights, this is fine if you are in arizona, but not new zealand!!!

All the shocks are the same unless you custom spec them otherwise....

For reference, my 350# front springs 8" long had a decent amount of preload at a "Low" ride height.

The 5" 550#'s I run now have the collar hand tight against the spring for the same ride height.

Same shock length.

Edited June 23, 2009 by E30-323ti

[|ncary 0]

A few disadvantages to changing the height with preload... There would be less droop and more inclination for the wheels to come off the ground during braking on a rough road.. I would like the most droop possible

Solving problems in this thread rocks!

[|ncary 0]

Dude dude dude. You don't get what I'm trying to say. I don't want a low, low, low car, I want the ability to raise and lower the car by the 6 or so centimeters the collar gives me. And if the shock stanchion was 2 inches further out i WOULD have more travel. Sigh.

[E30-323ti 66]

A few disadvantages to changing the height with preload... There would be less droop and more inclination for the wheels to come off the ground during braking on a rough road.. I would like the most droop possible

Solving problems in this thread rocks!

Thats a function of your shock length & spring rate.

You can't have a long shock & hard spring and expect to have plently of droop, because your starting spring rate is too high.

That is when you need tender springs to do the drooping.

Mine in the pic attached are 120# so they fully compress under the cars weight, then the main spring does the work.

[|ncary 0]

Red is spring. Blue is the collar travel. Left is how it is now, at MAX ride height. Right is how the shock should be, set up so Max ride height is matched to the spring lenght. The shock is as far out as it can go in both pics here.

*I'm confident both my front and rear will be captive with the longer springs I have over the standard kit. From installing the rear today it looks like it will be captive. The front 100000% is ahaa.

Edited June 23, 2009 by Incary

[E30-323ti 66]

Dude dude dude. You don't get what I'm trying to say. I don't want a low, low, low car, I want the ability to raise and lower the car by the 6 or so centimeters the collar gives me. And if the shock stanchion was 2 inches further out i WOULD have more travel. Sigh.

I get what you are trying to say, but there isn't a direct relationship between the height of the adjuster & the height change in the car.

At the end of the day, the spring has to be captive, that is the lowest you can go, up from there means spring preload, no matter how long the shock is!!

[bravo 35]

OK let me jump in here from what is maybe a little bit of a n00b perspective, but if you put the car on the springs now, they will compress, and the shock staunchion (as you call it) will not be at full travel. Wind the collars up a bit, and the car will lift, but the preload will not change until the car is at max ride height and the shock at full travel.

At this point, the suspension will be at full travel at rest which is not good, but I doubt this would be the case. And you would get good rebound over undulations as the spring would have preload at full travel (as it is supposed to).

In other words I think I get what the other two are saying, and I have either missed your point or you are having a blonde/senior moment.

Edit: as the post above - I would have thought they should be designed that no preload at full travel is near the bottom of the collar adjustment as they are, and that your ride height is set by the preload, or as Mike says - the springs won't be captive at the lowest height = unsafe and illegal.

[E30-323ti 66]

Red is spring. Blue is the collar travel. Left is how it is now, at MAX ride height. Right is how the shock should be, set up so Max ride height is matched to the spring lenght. The shock is as far out as it can go in both pics here.

*I'm confident both my front and rear will be captive with the longer springs I have over the standard kit. From installing the rear today it looks like it will be captive. The front 100000% is ahaa.

If the spring on the left has no preload, that is as low as you can go!! So there is no more droop than the spring/shock on the left...

It also means the spring is more likely to "block out" well before the shock reaches its bumpstops = real bad.

[|ncary 0]

I only need the spring to be captive when it is wound right up, for warrants and rough road thrashing. It doesn't need to be captive for the track, and that's how the kit is run in the states, non captive on the road and track. It's all pre-planned

[E30-323ti 66]

OK let me jump in here from what is maybe a little bit of a n00b perspective, but if you put the car on the springs now, they will compress, and the shock staunchion (as you call it) will not be at full travel. Wind the collars up a bit, and the car will lift, but the preload will not change until the car is at max ride height and the shock at full travel.

At this point, the suspension will be at full travel at rest which is not good, but I doubt this would be the case. And you would get good rebound over undulations as the spring would have preload at full travel (as it is supposed to).

In other words I think I get what the other two are saying, and I have either missed your point or you are having a blonde/senior moment.

Not quite, preload is the load applied to the shock when fully extended, so, if this equals the weight of the car, the spring will not compress when lowered down.

You are using the preload to raise/lower the ride height.

[|ncary 0]

If the spring on the left has no preload, that is as low as you can go!! So there is no more droop than the spring/shock on the left...

It also means the spring is more likely to "block out" well before the shock reaches its bumpstops = real bad.

No the one of the left can be lowered 1cm, which is how it is now in my lounge. 1cm of range is not enough, hence the need for longer shocks.

[bravo 35]

So you're saying you want several cm of travel with the spring not captive?????

[E30-323ti 66]

I only need the spring to be captive when it is wound right up, for warrants and rough road thrashing. It doesn't need to be captive for the track, and that's how the kit is run in the states, non captive on the road and track. It's all pre-planned

Not sure how many scrutineers will accept that, if at all, especially if you are meant to have a road legal car.

By all accounts a car that is too low & too stiff isn't going to handle well!!

[E30-323ti 66]

No the one of the left can be lowered 1cm, which is how it is now in my lounge. 1cm of range is not enough, hence the need for longer shocks.

OR do they need shorter bodies??

[JiB 0]

In my limited experience, I have not had or seen any scrutineers jack the car up to check for captivity. I'm sure I did the kemp rd hillclimb uncaptive and that was with the mg car club who are reasonably stringent.

Henry, my shocks were also too short. GC provided a tube of metal that you cut to size to space the bottom of the shock. Was this included somewhere in your kit? I'll try explain better - would moving the shock up from the bottom of the strut help? If so that can be easily done with a bit of tube.

GC provides this bit of tube so you can cut and weld your strut to whatever length you want and use the shock in a longer strut. Hope that makes sense.

[tire 10]

Haha I'm so confused by the recent converation in this thread, but its awesome and one day I'm going to understand and need it!

[CamB 48]

JiB - hopefully he has that the right length already for the spacer - it needs to be the right size to make up all the difference between the (short) bottom of the shock and the bottom of the strut so the shock is held firm.

Incary

- has the car been on the ground with the new front setup, in the position you show?

- is it too low?

I think you are worried unnecessarily about the lack of droop by the way. You'll note you have SFA at the back now.

Edited June 23, 2009 by CamB

[|ncary 0]

Yeah the spacer below the shock won't help, the shock is as high as it can go.

I haven't got them on the car, but I'll show you why this lack of shock extension is a concern for me. It's not to do with travel or droop. It's the fact that there is about 6cm of spring perch range and I can only use half of it. In the pic the rear strut is wound until just captive, I could lower the car 1cm (the shock won't be captive but it's not like I'll be hitting ramps and doing back flips, plus te big sway bar will keep it all together, this is how the kit was designed to run). The front strut is wound as much as I can do with my 22 year old fit muscles with the proper tool for leverage, that's the max preload I can attain. The ride height is going to change by sh*t f**k all, the collar has only moved 2cm or so, and that makes the spring more preloaded and the car sits what maybe 1cm higher? when it gets on the ground..

This is my only concern really. The travel will be fine how it is.

But, If the shock was lenghtened by say 3-4 cm, I could wind the perch right up and have it captive and nicely preloaded. With added bonus of more travel. And I could wind it down for track days, it won;t be captive, but the spring is not going any where is it? Especially with a 24 mm sway bar and the fact it has no where to go even if loose.

I see this as logical, I've never had 'adjusties' before, but from the hoards of setups I've researched, mine just seems wrong.

[|ncary 0]

For Ollie

Oh and sometimes a lot of bending back and forth to tear the metal can help...

[E30-323ti 66]

Yeah the spacer below the shock won't help, the shock is as high as it can go.

I haven't got them on the car, but I'll show you why this lack of shock extension is a concern for me. It's not to do with travel or droop. It's the fact that there is about 6cm of spring perch range and I can only use half of it. In the pic the rear strut is wound until just captive, I could lower the car 1cm (the shock won't be captive but it's not like I'll be hitting ramps and doing back flips, plus te big sway bar will keep it all together, this is how the kit was designed to run). The front strut is wound as much as I can do with my 22 year old fit muscles with the proper tool for leverage, that's the max preload I can attain. The ride height is going to change by sh*t f**k all, the collar has only moved 2cm or so, and that makes the spring more preloaded and the car sits what maybe 1cm higher? when it gets on the ground..

This is my only concern really. The travel will be fine how it is.

But, If the shock was lenghtened by say 3-4 cm, I could wind the perch right up and have it captive and nicely preloaded. With added bonus of more travel. And I could wind it down for track days, it won;t be captive, but the spring is not going any where is it? Especially with a 24 mm sway bar and the fact it has no where to go even if loose.

I see this as logical, I've never had 'adjusties' before, but from the hoards of setups I've researched, mine just seems wrong.

Stick them in the car with no preload and see what the ride height is.

If you don't know what this is (measure wheel centre up to the arch) as a starting point, you don't know that you actually want/need to run, ie. higher or lower!!!

I'm sure you've read Gustaves site on suspension geometry, so you will know there is no point dumping it into the weeds!!

With no preload, the car should settle/compress the springs ~2" (give or take, this is now your droop travel assuming 700#/corner).

With 2cm (0.8") preload ~280lbs worth, subtract that from the weight/corner = 420#

(1"/350#)*420#=1.2" the car should settle/compress the springs.

These are indicitive and do not take the motion ratio of the shock into account, so the amount of change at the wheels will be greater.

Once you have it all in the car, you should be able to man-up and wind the collar up further should you want a higher ride height.

The thing to watch with no preload (or even not captive *cringe*) is that you do not run out of bump travel in the shock, having a longer stanchion won't resolve this, the shocks would need a shorter body.

You may be able to shorten the strut housing if the insert is shorter than it. I suspect you will find the car will be plenty low enough with no preload/captive springs, you should measure the stroke of the shock to see how much bump travel you will have with no preload (ie. Stroke length - droop from above ~2").

You also want to make sure your spring travel (at a given preload) is longer than the stroke of the shock to ensure it doesn't block-out.

Edited June 23, 2009 by E30-323ti

[CamB 48]

My expectation (and the reason I keep banging on about putting them on the car) is that with preload wound up as far as your puny guns (I have the same problem - weak as piss) can manage that the front will be too high, which means you need to cut the struts and shorten them by approx 25mm. Then you should be happy, as you will have a further 25mm of lowering available.

Until you mount them on the car, I am only guessing.

You do know you need to get it realigned every time you raise or lower it, as the toe changes, right? It's not free.

Edited June 23, 2009 by CamB

[E30-323ti 66]

My expectation (and the reason I keep banging on about putting them on the car) is that with preload wound up as far as your puny guns (I have the same problem - weak as piss) can manage that the front will be too high, which means you need to cut the struts and shorten them by approx 25mm. Then you should be happy, as you will have a further 25mm of lowering available.

Until you mount them on the car, I am only guessing.

You do know you need to get it realigned every time you raise or lower it, as the toe changes, right? It's not free.

Depends how long his struts are of course.

We are all just guess-timating.

I know from when I ran 350#'s in the front, on the E36 koni coilovers, they had ~20mm preload for a 315mm ride height...