spring rates

Sun Jun 17, 2012 2:55 pm

I guess this has been covered a lot before but what coilover spring length and rate are people using on the front? im just about to order springs for my diy coilovers (

) and want to know what ballpark to aim for

gaz were saying 350lb and 6 inch but im not convinced i would want a bit less rate and more length

i recon i could fit 7 maybe 8 inch length and still have the tyre miss the coilover collar

what spring rates are ballpark for the rear in the standard location?

the car is a '90 m52 saloon 2 door for very occasional track mostly road use

i undersand this is a little overkill for primarily a road car but id like to get it right!

any help appreciated

cheers,
Matt

Mon Jun 18, 2012 1:14 pm

anyone?
mods could this possibly be moved to the technical section?

Tue Jun 19, 2012 3:11 pm

you can't fit a 7 or 8 inch spring IMHO. And you don't need to. Unless you got the shock / suspension travel to match.

I was running 5.5 inch long but 140N (800lbs ish) with a helper spring on top to keep it pre loaded when jacked up or on full drop

350lbs for a road car seems about right to me. Not too firm but stiff enough to take body roll out. but I wonder if you are not going to bottom the shocks out with this "soft" spring. What shocks and top mounts are you going to use?

Tue Jun 19, 2012 4:41 pm

UweM3 wrote:you can't fit a 7 or 8 inch spring IMHO. And you don't need to. Unless you got the shock / suspension travel to match.

I was running 5.5 inch long but 140N (800lbs ish) with a helper spring on top to keep it pre loaded when jacked up or on full drop

350lbs for a road car seems about right to me. Not too firm but stiff enough to take body roll out. but I wonder if you are not going to bottom the shocks out with this "soft" spring. What shocks and top mounts are you going to use?

hi mate,
when you say 140N do you mean 140N/Cm?

800lbs/in! wow that is is solid!

the spring at the moment is 8 inch long, the damper extends hapilly to this length at the moment. i have a choice between spax and koni dampers. i cant afford h&r at the moment!

the top mounts are spc adjustable solid mounts...although these have worn i would like to replace them with rpm jobbies

did i recall you saying you had a diy coilover setup yourself? do you have alink to the thread if so?

thanks for your help,
Matt

Tue Jun 19, 2012 5:01 pm

this is my DIY coilover next to a standard M3 strut (which has stroke shortened Bilsteins).

Both legs shown in this picture have the same rebound length.

Can yousee the flat wound helper spring on top? This will fully collaps when the cars weight is on the strut.

Your damper will not extend all the way up (out) when the car is sitting on it's wheels, keep that in mind. You need some "negative" travel in your suspension when going over bumps or your tyre will loose ground contact.

That is a picture with the car sitting on axle stands.
The position of the lower spring perch is NOT where it finally ended up, this was just wound down to fit the springs without tension. The real setup is about 2-3 inch higher up

What is your rear setup? ARB's?

I still have the Billie's from the struts shown above but think the rebound will be too short for what you are planning to run.

And yes, 800lbs is stiff. But the speed you can turn in with a setup like this is staggering

I think you are making yourself more trouble than you need with coil overs just for a road car. A good set of springs and dampers is doing the trick just fine.

Tue Jun 19, 2012 6:28 pm

very nice, and interesting!

why would you say you couldnt have a 7 inch spring? your 5.5 inch spring has a 2 or 3 inch helper on the top it seems?

i was going to work arbs into the car as an afterthought - do you have a reccomendation? i imagine with a setup like that there is no need for you to run one?

my springs are kaput so i figure its not much more to make a coilover setup than buy some new boingers!

thankyou,
Matt

Tue Jun 19, 2012 6:36 pm

The helper spring is VERY soft and is only there to keep the spring located between the spring perches.
Only the main spring is doing the work.

Have you already converted your legs?

Tue Jun 19, 2012 7:08 pm

Hi Matt, off the top of my head I cant rember the length and rate of the springs I have used. The thing that I can remember is you have to be real careful about the length of the finished coil over. The strut itself needs to be shortened, which in turn means the shock insert needs to be shortened too. This is because of the top mount, in standard form the top mount sits down below the spring due to the shape of the top spring cup (see the first pic that Uwem3 posted).

It means when you start lowering you are losing more and more travel the lower you go. You can get down to to a good hight but you are left with about 40mm travel which will mean you will hit the bump stops frequently unless you have some real strong springs either are undesirable on a road car.

It looks like the custom top mounts Uwe has on his would help.

You really have to do alot of measuring, it is not as simple as welding threaded tube to your struts adding a spring and perch. I'm not trying to pi55 on your chips, but I was real peaved when I had to take apart the ones I made to shorten them.

God luck

Tue Jun 19, 2012 7:12 pm

I think you are making yourself more trouble than you need with coil overs just for a road car. A good set of springs and dampers is doing the trick just fine.

Having done this, I have to agree. But I can also understand, yes sometimes its fun to make stuff

[/quote]

Tue Jun 19, 2012 7:43 pm

maggspower wrote: Hi Matt, off the top of my head I cant rember the length and rate of the springs I have used. The thing that I can remember is you have to be real careful about the length of the finished coil over. The strut itself needs to be shortened, which in turn means the shock insert needs to be shortened too. This is because of the top mount, in standard form the top mount sits down below the spring due to the shape of the top spring cup (see the first pic that Uwem3 posted).

you are right, with the rubber top mount used , I don't think you can run this without bottoming out.

maggspower wrote: It means when you start lowering you are losing more and more travel the lower you go. You can get down to to a good hight but you are left with about 40mm travel which will mean you will hit the bump stops frequently unless you have some real strong springs either are undesirable on a road car.

the bump stop is the least of your problems. You will hit the Alli top spring perch on the gland nut. Ask me how I found out....

I have seen converted struts with a huge rubber bump stop fitted and basically the car was running on the bump stop all the time! It's like fitting a harder spring (why not in the first place???)

maggspower wrote: It looks like the custom top mounts Uwe has on his would help.

yep, they will give you up to 40mm suspension travel back if the right type is used. Basically the flatter the mount, the more travel you gain.

maggspower wrote: You really have to do alot of measuring, it is not as simple as welding threaded tube to your struts adding a spring and perch. I'm not trying to pi55 on your chips, but I was real peaved when I had to take apart the ones I made to shorten them.

God luck

fully agree with you. Not worth the hassle IMHO if you don't want to run a stiff track biased setup.

Tue Jun 19, 2012 8:08 pm

800lb and only 5.5" those are very cool! I would have expected the coils to be thicker at that length, just shows how far along metals have come.

Tue Jun 19, 2012 9:04 pm

UweM3 wrote:
Have you already converted your legs?

nope not yet im just planning. ive bought the perches though

i do have the spc top mounts

( http://www.ca-automotive.co.uk/variants ... 3Ng==.html ) ,

which do away with the rubber part of the top mount and im hoping will allow me to work this idea.

(dont buy them by the way, terrible design)

Tue Jun 19, 2012 9:08 pm

randomspeedfreak wrote:
UweM3 wrote:
Have you already converted your legs?
nope not yet im just planning. ive bought the perches though

i do have the spc top mounts

(http://www.ca-automotive.co.uk/variants ... 3Ng==.html) ,

which do away with the rubber part of the top mount and im hoping will allow me to work this idea.

(dont buy them by the way, terrible design)

Those look like they add a lot to the stack, I bet they are no shorter than stock rubber top mounts that must be at least 40-50mm if not more!

Tue Jun 19, 2012 10:50 pm

Demlotcrew wrote:
randomspeedfreak wrote:
UweM3 wrote:
Have you already converted your legs?
nope not yet im just planning. ive bought the perches though

i do have the spc top mounts

(http://www.ca-automotive.co.uk/variants ... 3Ng==.html) ,

which do away with the rubber part of the top mount and im hoping will allow me to work this idea.

(dont buy them by the way, terrible design)
Those look like they add a lot to the stack, I bet they are no shorter than stock rubber top mounts that must be at least 40-50mm if not more!

I have the same ones, they are the same hight as the standard rubber mount.

Wed Jun 20, 2012 8:59 am

randomspeedfreak wrote:
UweM3 wrote:
Have you already converted your legs?
nope not yet im just planning. ive bought the perches though

i do have the spc top mounts

( http://www.ca-automotive.co.uk/variants ... 3Ng==.html ) ,

which do away with the rubber part of the top mount and im hoping will allow me to work this idea.

(dont buy them by the way, terrible design)

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