DIY Coilovers

[Rusty]

From my investigations, stock springs are slightly stiffer at the rear. Most people I've looked at threads from on motorgeek and a few people I know on here have gone softer up front or the same all round. Chassis setup is a personal thing, so if you prefer stiffer springs up front and have tested with many different ones then that's your preferred setup, I might like the car to handle differently and Terry differently again. My feelings are that I prefer a car not to understeer and I've found that the HnRs, with softer rear springs, have made it understeer more than the stock springs, hence aiming for this setup, if I go for coilovers.

[andy10v]

Have you read speeding-g60's DIY coilover thread on motorgeek?

http://www.motorgeek.com/viewtopic.php?f=11&t=26499

I dont think the Koni's will last long with some 400/500lbs springs if i am honest.

How stiff do you reckon you could go then? Could you get a set of shocks re valved or is that cost prohibitive?

[terrybullwon]

I dunno i am only a Chef.

I was warned by people who build suspension they did'nt share everything i wanted to know

Re-valaving would be the thing to do thats for sure but i dont know if those koni's for the coupes are fully rebuildable?

[Rusty]

Cheers for that link, interesting to have a look through

[Error404]

I've considered making up some DIY coilovers simply to get the perfect ride height a slightly stiffer than stock fixed rate spring, easily within the capabilities of a set of off-the-shelf Konis.
The budget option for stiffer springs is get some Billies re-valved to suit chosen spring rate, don't think it can done with Koni adjustables (for worthwhile cost anyway)
Could get some fixed rate customs made up for a couple hundred quid a corner. Really you need to spend a couple of grand to get a set of proper adjustable matched dampers

[andy10v]

I dunno i am only a Chef.

I was warned by people who build suspension they did'nt share everything i wanted to know

Re-valaving would be the thing to do thats for sure but i dont know if those koni's for the coupes are fully rebuildable?

Only a Chef?

[newsh]

Andy, I didn't know your spring project had foundered, thats a shame. How many sets were you short? Maybe PM me and we can discuss..

[Rusty]

There was interest in about 5 sets and I'd have had to make 25. I'd estimate it would cost about £200 a set so it adds up very quickly! Give me a shout if you want to, happy to discuss it and see what you think.

[Rusty]

Just done a spreadsheet to enable spring calcualtions for rideheight, helper springs and free lengths

Looks like longer than 4" helper springs are required for ~HnR levels of ride height drop (20-25mm) over 450lb springs up front, using 40lb+ helpers. For values less than 450lb, the front is fine, over 450lb and the springs are not long enough for the strut (this is for my Konis and is only by a few mm).

I have based this on the unloaded weight of the HnRs, as they are virtually unloaded when off the car. I'm sure that with some measuring, things can be moved quite a bit, I just need to see a strut off the car before updating the information.

I have used 4lb helpers, instead of 50lb, to help things for rates over 450lb. The Helpers are fully compressed by 6kg and do nothing until a downward wheel travel of 50mm or sofor the 500lb springs.

The rears are OK for all sensible spring rates and rideheights

Personally, the HnRs sit as low as I'd want to go. I've based my calculations around a rideheight about 15mm lower than stock, 10mm higher than HnRs, to try and help with the camber change under load. Lowering the car much more than the HnRs leads to excessive rear toe, as Ciaran has found out to his cost.

Edit:-

Just updating the spreadsheet for strut lengths. From this picture, it looks like the unloaded length can be reduced easily by ~50mm up front!

[Rusty]

Updated spreadsheet for perusal & comment. Use at your own risk!

[Error404]

good work Andy, what did you work out the OE spring rates were when you were looking at springs?

[Rusty]

There's a few threads on the forum that have the spring rates in them.

OE coupe are approx. 200lb front and a tad more at the rear.

HnRs are about 210lb front and 200lb rear.

At last, a very helpful person has confirmed actual H&R RS2 spring rates.
They are progressive and rated as follows:

FRONT 43 N/mm [16.2% stiffer than OEM, 37 N/mm]
REAR 55N/mm [5.8% stiffer than OEM, 52 N/mm]

As spring rate is governed by d^4 / D^3 and the avant springs have a marginally larger d (14mm vs. 13.5mm) the coupe spring rate is IIR 90% of the Avant items, thus around 200 lb/in.

Avant rear suspension is not related to the coupe, thus that value can be ignored. The dimensions of the rear springs give a similar stiffness to the front.

http://www.s2forum.com/forum/showpost.php?p=486150&postcount=10

Various threads -

http://www.s2forum.com/forum/showthread.php?t=38409

http://www.s2forum.com/forum/showthread.php?t=37203

For a road setup, you'll want to go to around 250lb front and whatever your chosen rear setup is. For occasional track use, you'll want to head towards 300/350 and for a track day toy, about 400/450 with the balance adjusted for driving style and weight distribution. For a dedicated track car, as per TerryB's post, 500 or even 600+ is perfectly plausable, if you're racing in some billiard smooth UK tracks.

Here is the spreadsheet updated with 200/225 and 250/275, for road setups. There's still a need for helper springs, although, after some further calcualtions, the deficit is <1" for a 10" spring and so is only relevant for extreme wheel travel or servicing and could be overcome with a modified top cap, designed with a deeper spring retainer.

[cooperquattro]

dont forget that air con models have stiffer front springs...also were you calculations done using new oe springs?

[Rusty]

As above, calcualtions / measurements etc. were approximate. The stock springs are only for a reference value and the springs I measured were air con springs.

The addition of aircon to the 950kg front axle load isn't going to contribute much more than 30kg, or approx 3%.

I have never seen data to prove that the air con springs are stiffer, it's entirely possible that, due to such a small increase in load, they are a slightly longer free length, to allow for more sag when loaded and thus keep the rideheight correct for the marginally heavier air con model. Equally, having removed the air con system, I can't say that there was any noticeable change in rideheight or handling on my car.

Thinking about sag for a 3% increase in load:-

For a front axle load of approx 475kg = 1045lb.
Sag is approx 1045/200 = 5.2" ~ 133mm
3% of 133mm ~ 4mm difference in rideheight / sag.

Anyway, standard springs are for a reference only and if the air con springs are stiffer, they still measured softer than the stock rears and thus standard fronts would be softer again. Either way, the front and rear springs are approiximately 200lb each and the rears are marginally stiffer. I should get the collection of springs that I have tested by a mate at my onld Mech Eng department, see what's what...

[Error404]

I am seriously considering this now, I have a spare set of S2 strut housings so will dig them out and have a look at it with a view to coming up with an easy DIY fabrication using parts off the shelf in the UK