Suspension upgrade

[handpaper]

By popular demand (well two or three of you at least ) here's a photo-journal of my suspension build.
A hefty package from Gaz arrived this afternoon, just as I was leaving for work, so I've had to wait until I got home to inspect it

Here's exactly half of what was in it



And in detail...
A threaded tube with spring seat and locking ring, for slipping over a front strut, also a top cap (left) and adaptor ring for joining the main and tender springs together:



The tube has an inside diameter of 51.5mm and is a close sliding fit over a front strut tube.

Here's the bits assembled, with springs I bought earlier:



In operation, the flat section tender spring (blue) will normally be fully compressed, opening only when a wheel would leave the ground otherwise.

This is Gaz's coilover rear shock. The threads are machined into the shock body and it's supplied with the spring seat, locking ring and top cap.



A closer view of the bottom end of the shock, showing the spherical bearing bottom mount and adjuster (48 steps and yes, I was sad enough to count them)



Beautiful engineering - billet alloy top mount, fitted with a spherical bearing.



Here's the rear coilover ready to fit. It's probably a good idea to reinforce the rear turrets first, though.



How much?
The front conversion kit of tube, spring seat and locking ring is £13.50 a side, the top cap another £8.50
The main=tender/helper adaptor is £4
The rear coilover shock is £70 (major bargain!), the top mounts £42.50 each and the springs £16 each.
The main springs shown were a lucky eBay find; £18 the pair, delivered.
The tender springs were annoyingly expensive - £55 delivered from Faulkner. Very few people make flat-section springs and all of them hate doing it (they're wound from flat wire, which is, apparently, no fun at all).

All in, I've spent around £450 so far. I'll probably buy two more pairs of springs for road use, and I may put Gaz front shocks in too, as the Konis limit front suspension travel a bit more than I'd like.

Tomorrow I'll prepare the front struts and weld on the threaded tubes - update probably won't be until tomorrow night or Wednesday as I'm working every day this week

[Theo]

Very nice indeed, I'm really looking forward to seeing how the car sits when it's all fitted.

[handpaper]

I'll post an update tonight showing the front strut conversion; too busy doing it to post now!

[handpaper]

OK, as promised, here's the conversion.

Starting with a standard front strut:



I removed the caliper, carrier, backing plate, spring and top mount to leave this:



As you can see here, the threaded tube is a close sliding fit over the strut tube:



The next step is to cut off the spring seat. Using a 9" angle grinder with a thin (3mm) slitting disc, I cut just above the weld, being careful not to cut too deep - not even all the way through:



Some persuasion with a lump hammer cracks the remaining thickness:



A little more cutting and hammering and the spring seat is off - with no material removed from the strut itself:



Next, I ground the weld back flush with the strut tube. This one was done with a grinding disc on the angle grinder - not much fun being delicate with a heavy tool. Afterward the paint was stripped off with a cup brush on a small angle grinder and the ground section finished by hand with a file.



Here's both struts ready to have the threaded tubes welded on. I ground off the weld from the one on the left with a bench grinder - much easier.



Ready for welding - the threaded tube is resting on the brake line support bracket, as it's at just the right height



Both tubes welded on. Not the prettiest welds I've ever done, but they are solid. I'm not sure as yet whether to weld around the tops - the strut is quite thin there and may distort if it doesn't hole through. Might be better just to seal it with silicone - structurally the bottom weld is quite adequate.



Lastly, here's the strut assembled and (nearly) ready to fit. Ten brownie points to the person who can tell me what's missing (and it's not the top mount:) )

[UweM3]

I have done the same conversion with parts from Rallye design. What spring rates are you going to use?
I have a few springs left if you need someting to play with (400lbs 5" long and 450lbs 4"long)
Really looking forward to hear what ride height you will have once assembled, I never managed to get it down even to stock height without loosing all suspension travel. (what front top mounts you're using)
Keep the threaded tube covered in grease all time, mine was completly seized after 2 month on the road and I had to cut the alli adjusters off.

[Theo]

Looking good James, get it all bolted on to the car ASAP! How did you get on with the collar nut, did it need alot of grinding to clear the inside of the spring? Is that what's missing in the pic!!?

[handpaper]

Springs are 225 lb/in 10" rear, 650 lb/in 6" main + 90 lb/in 4" tender front, though I may use slightly longer fronts later. The idea is to duplicate H&R's 'Ring kit.
I'll be buying some longer, softer springs for road use, something like 200 lb/in 12 " front, 140 lb/in 10/12" rear.
If I remember correctly, your conversion had the threaded tube resting on the stub of the OE spring seat, which would limit how far the system could be adjusted.
Top mounts are OE at the moment; I still haven't finished the adjustables I'm building (to your design!)
Yep, Gaz did mention protecting the tube with grease. Steel rings might be a good idea here as they would avoid the galvanic corrosion from placing dissimilar metals in contact, but people seem fixated on the twenty gram weight saving aluminum gives

[UweM3]

Springs are 225 lb/in 10" rear, 650 lb/in 6" main + 90 lb/in 4" tender front, though I may use slightly longer fronts later. The idea is to duplicate H&R's 'Ring kit.
I'll be buying some longer, softer springs for road use, something like 200 lb/in 12 " front, 140 lb/in 10/12" rear.
If I remember correctly, your conversion had the threaded tube resting on the stub of the OE spring seat, which would limit how far the system could be adjusted.
Top mounts are OE at the moment; I still haven't finished the adjustables I'm building (to your design!)
Yep, Gaz did mention protecting the tube with grease. Steel rings might be a good idea here as they would avoid the galvanic corrosion from placing dissimilar metals in contact, but people seem fixated on the twenty gram weight saving aluminum gives

My conversion was exactly like yours, spring perch cut off and the threaded tube as much down as possible. It's not really the length of the spring causing you trouble, it's the availabe travel of the shock. I predict you will not get the car down to your desired ride height with the stock top mounts AND having enough suspension travel left. (but I am very happy for you if I am wrong on this )

Your OEM spring is somewhere around 100lbs max and 650 spring will not compress much with the cars weight when static. You will have to lower the platfrom to get the front down. But I want to save myself typing too much, I will wait till you have it on the car.

Also a 200lbs 12" long for the front will not work IMHO, it's 300mm long and your total spring travel is not even half of that. The spring will get coilbound.

PS any other coilover strut I have measured so far has a shorter shock insert to regain lost suspension travel. KW for example is 40mm shorter than the M3 strut (measured bottom to collar nut of tube)

PSS even by welding the threaded tube as low as you have you won't be able to wind it down that much. the spring will most likely not clear yout tyre/wheel. Unless you're running something small with a lot of offset.

[handpaper]

Ten brownie points to Theo!
The shock collar nut needed to be ground down from 63mm OD to under 55mm to clear the springs.



A warm and unpleasant job with the bench grinder. Far better suited to a lathe, but I don't have one

Anyway, here's the struts assembled with shocks and top mounts; adjusted for height and ready to install



Uwe, I think we may have a misunderstanding here - I'm not trying to get down to -70mm; I'd be happy with -40mm or even less.
-70mm is where I calculate I'll be by splitting 125mm of shock travel into 55mm of bump and 70mm of rebound.

Good guess on the OE spring rate - according to the definitive list on e30tech.com it's 106 lb/in (M-Tech is 118).
The 650 lb/in spring will compress 30mm under static load as opposed to the OE spring, which will compress 182mm (assuming 53/47 front/rear weight distribution and a total weight of 1300Kg).
But the OE spring is 14" long.
14" (356mm) sagging 182mm is 174mm.
My main spring is 6" (152mm) long; under load it's only 122mm - a drop of 52mm compared to the OE spring. Add the block height of the tender spring (30mm) and the adaptor (4mm) and the drop is only 18mm. Unfortunately, in order to let the tender spring provide extra rebound travel, I must wind the spring seat down to below the OE height and this is what gives the -70mm ride height. I can wind the spring seat up and regain some ride height (and ground clearance!) but only at the cost of rebound travel.
I should have everything fitted on Saturday, I'll post pics then

RE: PS : Interesting - they must cut the strut tube short and re-thread it. Here's another way

RE: PPS I'll be running 195/50/15 Kumho trackday tyres on 15" BBS rims - we'll have to see

[mikekean]

ive heard if you run any wider than 195's on 7 inch bbs with rear coilovers you will need to run a spacer.

[handpaper]

ive heard if you run any wider than 195's on 7 inch bbs with rear coilovers you will need to run a spacer.

Thanks for the heads-up there - I never considered clearance issues at the rear!
195/50/15s on 15" BBS should be OK then

[UweM3]

Handpaper,
as posted previously I am very happy to be wrong and everything works as youhave planned. I am just sharing my experiences with you. I wasn't implying that you lower to -70, I had trouble to get down to -25mm (from M3 height) without the top hat hitting the collar nut under heavy load.

Just forget about the springs for a moment and visualise your strut with the shock and fitted to the car. The ride height/travel of the shock doesn't change whatever spring you use. Let's say you have the ride height set to whatever you want it, i.e -25mm over stock. That position is independent to the spring used, now you add a top hat which guides the spring on the INSIDE with a 10-12mm collar, you will have to substract this from your remaining travel as well. Unless there is a fundamental difference between the M3 and the standard E30 setup you may find that you run out of suspension travel under hard load even if you just lower moderate.

There is still the possibility that I am a complete moron and have done something wrong when doing my conversion and I am happy if your setup works (which means I can find out why mine didn't work and correct it)

Also, I can't see a bump stop in your assembly?

PS about the strut cutting as per GC setup, they cut between the thread and tube and weld the two sections back together. Not my cup of tea
Thanks for the pictures and efforts, much appreciated.

PSS about the link to Gustave's site, that's about the rollcentre and is a seperate issue IMHO

[hoshy]

handpaper - this is very

[e21Jason]

Good work

When doing this on the e21 most guys use the golf mk2(51mm) shocks which are 50mm shorter and cut the struts shorter, I am sure there are other shorter 51mm sturts you could use to get teh suspension travel back.

Jason

[agent006]

Lovely sofa too.

[handpaper]

Uwe, your advice is always welcome. I'm learning as I go here and any help you can give me will be appreciated. Please don't think I'm arguing with you if I don't see things the same way - sometimes seeing for myself is the only way I'll get it

There are two things currently limiting suspension travel. One is, as you said, the top cap. I didn't realise that its shape would cost me so much - 20mm lost there takes me down to 105mm of travel. Longer shocks are the answer - does anyone want a pair of third-hand Koni adjustables?

The other is the main=tender adaptor. It's a plastic tube with a flange on the outside half way up and its internal diameter is too small for it to fit over the threaded tube.
I could weld the two springs together for a quick fix, but I may want to change the main spring at a later date and don't want to have to buy another pair of tender springs when I do. I'll have to make up an adapter that is either thinner on the inside or holds the springs from the outside instead.

Bump stops on order

Cut and shut a strut tube? Somebody point GC at a plumbers/gasfitters supply catalogue. They want an M48x1 pipe tap. If it doesn't exist, having one made would still cost less than all that careful welding!

No pics today as I've been building camber adjustable top mounts to (something like) Uwe's design. It's his idea and a bloody good one, so I won't be showing the world how it's done.
I will say, however, that cutting 4mm mild steel to shape with a jigsaw is NO FUN!

[Brian28]

I will say, however, that cutting 4mm mild steel to shape with a jigsaw is NO FUN!

That's why God invented angle grinders . We raced with a very similar front set up last season but didn't use helper springs, standard rear set up with harder springs, and fixed top mounts re-welded for max neg camber. Although there are a load of ways that its not perfect, including suspension travel as Uwe says, it works plenty well enough. I had Koni adjustable fronts, he had AVO, I got 8th in the championship he got 3rd, loads of cars with "proper" suspension behind us so nothing wrong with budget stuff.

[UweM3]

Handpaper, the total shock travel isn't so important. When you are at ride height you will run on the lower 30mm of travel. I was surprised when I lowered the car on wooden blocks without the spring in place how little suspension travel was actually left.
I have seen conversions like this from somebody else and they run the suspesion on the bump stop ALL times.
The bump stop actually is part of the spring rate and acts like a progressive add on spring to support the main spring under heavy load. But it's not meant to be part of the spring all time, just to get the spring rate up when loaded very heavy and to stop the spring getting coil bound.

I was thinking to make another tophat which holds the spring on the outside instead of inside but have decided to use different top mounts to gain 25mm of travel.

I am going to use almost same front spring rate as you and that will most likely help to cope with the limited suspension travel. A 650lbs spring will not allow a lot of travel anyway but it may not work if you plan to use a 200lbs spring

Can you please explain how you worked out the different travel of OE spring and 650lb spring on static load?

I have bought KW springs this time, the are slightly larger ID and have less coils at same height giving more travel before getting coil bound (and are lighter, too) but they are £Â£Ã‚£Ã‚£Ã‚£ The bigger ID will get rid of the problem you found with the plastic joiner not slipping over the threaded tube.

I want to assemble the lot first without any threaded tube, just a ring on the strut with a static platform. I can add spacers to move the spring platform up and down but need to find out how much the spring will compress at static load. I might even leave it like this if the handling is good, in the end the springs I have fitted now are non adjustable and that works. Just means a lot of in and out till the static ride height is ok (but I have thought about a quick change solution already)

I don't want to spend too much money now just in case it's ending up crap again. If that happens I will get the credit card out and buy a proper set of GAZ's finest

here a picture of the strut I made first. No bumpstop to show remaining travel with a 450lbs spring and just lowered 25mm from stock M3 ride height

[handpaper]

Brian - angle grinders are great for cutting straight lines and around the outside of things, but to cut inside curves you need a laser, plasma or water cutter, or, if you don't have those things (as I don't ) a jigsaw will eventually do the job.
Tender springs are for 'Ringers and other maniacs who want a very stiff setup, but still want to be able to abuse kerbs and keep the wheels on the ground over crests - they let you have plenty of rebound travel with a very hard main spring.

What series were you in? Will I see you at Castle Combe on Monday?

Uwe, I've just (00:15 22/03/08 ) realised that I've made a huge mistake that, luckily, doesn't change anything except for the better!
My assumption (goodness knows why) was that the Koni adjustable shocks I'm using topped out at standard ride height.
Thus, any rebound travel I built into the suspension would have to come off the ride height (70mm rebound travel = 70mm drop).
They don't - and it was your question about spring travel that made me realise it!
The OE spring has 14" free length; when installed it's compressed to 10.5", under static load it's down to 7". Therefore, the OE shock (165mm excursion) has travelled 3.5" (89mm), giving a 'shock height' (and, of course, remaining travel) of 76mm.
So if the OE ride height is 76mm, and my Konis top out at 125mm, providing 70mm rebound should result in a drop of only 21mm!
You were right, I was wrong , and I'm delighted!

Moving on, an outside tophat sounds useful - the difficulty is that springs are specified by their inside diameter. My main and tender springs have identical ID, but because the main is wound from 12mm wire and the tender from 10mm, the ODs differ by 2mm. A round shim outside the spring would solve this, but how much trouble do you want to go to?
I'd be very interesed to see how different top mounts could increase suspension travel, though.

To use a lighter spring, one must emulate the OE suspension to a degree and preload it - wind up the spring seat so that the spring is under compression with the shock fully extended.
I'll work the example for a 150 lb spring.
The front of the car weighs 53% of 1300Kg (for a 6-cylinder). Stripping doesn't change this much, especially as most lightening happens in the middle or rear. This gives a static load of 758 lb per front spring. If you were to install a 12", 150lb spring into a coilover conversion with OE shocks, such that the spring was only just held in place, it would sag by 128mm and effectively lower the car by 39mm. To bring the car back to standard height, you would wind the bottom spring seat up by 39mm, putting the spring under 230 lb of compression at full shock extension.

Spring compression at static load is given by Hooke's law : movement=load/rate; a 200 lb/in spring will compress 1" under 200 lb of load, 2" under 400 lb etc. So a 200 lb/in spring with 12" free length will compress to 10" under a 400 lb load.

Whether the larger ID on the KW springs will help or not, I'm not sure, but wouldn't think so. The problem is with the adapter, not the springs.
Coil-bound isn't an issue - just use longer springs and wind the lower seat down!
I think you're probably better off using a threaded tube anyway, the springs are designed to fit over it and adjustment will always be easier than any spacer-based solution - especially if, as above, you need to put the spring into compression.

Today's activities started late as I didn't have to get up and take the boys to school (zzzzzzzz). My big problem was the spring adaptors fouling the shock collar nuts and the threaded tubes.
So, starting with a strip of 0.8mm 304 stainless steel :



I cut and bent tabs to locate it between the springs :



coiled it up into the right shape



clamped it in position :



and welded it :



(not on the spring, it's just refitted to illustrate)

Here it is installed on the strut:



Fitting it all today (Saturday)!

[Dan318-is]

What a great article

[tomson]

OK, as promised, here's the conversion.

Starting with a standard front strut:

That looks familiar

Cracking work too James

[Brian28]

Brian

What series were you in? Will I see you at Castle Combe on Monday?

PBMW the last two seasons. Spent the last 3 days flat out trying to prep two cars, off to the garage again shortly, they should be ready but not finished/detailed as we would like them. I'm not racing this season but will be loitering around the paddock, probably Quarry when the cars are on track. My brother will be having his first drive in a 318 (black/silver 24) engine goes in this afternoon, the other car is a 320 that a guy is doing a rent a drive in as his own car isn't ready, calypso red 57, will be his first race and first time driving the car. Should be interesting to watch, I'll have my fingers crossed that nothing drops off as running in and test miles will be driving the cars on and off the trailer.

[UweM3]

These are the springs I am going to use. Left rears (not coil over) Right Front

[handpaper]

Oooohhhh - pretty!
Are they still 2 1/4" ID? If so, you're still going to get the problem with the adapter ring

Sorry about the lack of updates, I've had a rather "full" few days!
I finished the last fabrications on Saturday; reinforcement plates for the rear turrets and grinding the shock collars down to 50mm diameter. This further reduction, along with the outside spring adaptors, bring back almost all the lost shock travel
I didn't try to fit the kit that day. I couldn't do it Sunday either, and Monday was spent at Castle Combe (good day out - but take your own food).

So bright and early Tuesday morning I start work.
I decided to do the rear first, as it was all bought-in parts that should fit easily, right?
Wrong. The rear top mount holes need slotting outward by about 5mm, or the springs foul the chassis at full extension. This took me over an hour to diagnose - for each side! See, I started with the RHS, where there is also a metal plate protecting three breather tubes:



Because of the amount of clag covering the area, the plate wasn't immediately obvious.
I then spent just as long trying to work out why the left wouldn't fit, either

Eventually all was fitted, the reinforcing plates complicating matters slightly, but I'm sure they'll be worth it.



In comparison, the front was a doddle - even easier that fitting an off-the-shelf drop kit as no spring compressors of strut disassembly was required, just bolt off and bolt on
Here's the wheel clearance with a 40mm drop and 195/50/15 tyres:



Another 10mm is possible with these tyres, but 205/55 is too big to drop further than about 30mm. Good enough.

With a 40mm drop (which is more than I'll use on track) and the front struts cambered over on the adjustable top mounts, she looks like this :



The back is down as far as it will go without using helper springs.



The front will go 10mm lower



Further modification on the front top mounts can get me even more camber, but this isn't bad.

[Theo]

Seems like a good end result then. How much clearance do you have from the outer edge of the tyre to the strut? I'm currently using 215-50-15's, looks like they will be too wide for this setup, i'd want the car to be a good 40mm lower than standard on track. I did just get some bargain 195-55-50 r888's off ebay, so maybe I could just run these on the fron with the 215's at the back..

Anyway, how does the car feel with the new suspension?

[mikekean]

looks pretty good. so what have do you actually gain from coilovers apart from height adjustability?

[Brian28]

Room for a lot more front neg camber, with standard diameter springs movement is limited as the springs hit the inside of the bulkhead.

[iguana]

+ far easier & cheaper to change spring rates

[handpaper]

Both of the above, plus slightly reduced sprung and unsprung weight.
Springs are £15+VAT each from Rally Design and changing them is easy - in most cases you don't even need spring compressors as the spring goes on loose and can be preloaded if necessary with a C-spanner on the bottom spring seat (that's why the threaded tube goes so far down the strut )

Theo - the thing about coilovers is that they're adjustable and you can swap springs easily. The length of my main spring/tender spring combination dictates how far down I must wind the adjusters to get a particular drop. If my spring(s) were shorter, the adjusters needn't go down as far.
Check elsewhere (Pooky on northloop seems to know his stuff) but I think you should be OK with a 4", 100 lb/in tender and 5", 700-750lb/in main spring. This should let you get the drop you want, without having the bottom spring seat and locking ring foul the tyre. I don't think your Bilstein shocks will be up to this spring rate though - get some Gaz adjustables.

What's it like to drive?
No squat under acceleration, almost no dive under braking, body roll? What's that? Understeer when turning-in is gone.
Roadholding is awesome.
The downside is : noise from the spherical bearing rear top mounts, inability to take speed bumps at over 5 mph (unless you don't mind taking off and crushing lumbar vertebrae), discovering that even newly-surfaced roads aren't really flat.
I'm going to have to buy some softer springs, with this setup it's no longer a road car.

[UweM3]

I'm going to have to buy some softer springs, with this setup it's no longer a road car.

or do what most of us have ended up with, buy a trailer

PS what offset rims are you running? seems to be very close to the strut for such a narrow rim.

[handpaper]

Wheels are standard 15" BBS, as supplied with the car!
The photo isn't from the ideal angle; there's actually about 10mm of clearance.

Trailer + tow vehicle + extra 'Class E' driving test = £Â£Ã‚£Ã‚£Ã‚£Ã‚£Ã‚£Ã‚£Ã‚£
Extra set of springs = c.£100 delivered
Guess which one I can afford?

[UweM3]

Wheels are standard 15" BBS, as supplied with the car!
The photo isn't from the ideal angle; there's actually about 10mm of clearance.

Trailer + tow vehicle + extra 'Class E' driving test = £Â£Ã‚£Ã‚£Ã‚£Ã‚£Ã‚£Ã‚£Ã‚£
Extra set of springs = c.£100 delivered
Guess which one I can afford?

that's an easy one!

I have a set of 400lbs spring if you want to try theese for the fronts.
don't think you need to go lower than that, I am running 350 and have driven to the ring several times. Not too bad. But it depends much more how stiff your shocks are.

[JimmyC]

class E driving test, whats that all about

[UweM3]

class E driving test, whats that all about

car and trailer license (at least it has one benefit to be older...)

[JimmyC]

when was that introduced?