My Estate - GSi conversion

[Alex_FC]

Just to add my 2p

Cutting the length of a spring changes the Spring constant 'K'. Infact it makes the spring much stiffer as the remaining spring steel has to strain more for the a given deflection 'Delta Length'.

So the matched spring and damper setup the car came with as standard has been lost, You now have a sub optimum setup! Great for looks, not great for ride quality or handling charateristics.

Also as the spring steel is straining more, more likely the spring with fail in some catastrophic way.

None the less, following rules and not doing something because it may be dangerous is for whimps. I love the car, love the look and would happily drive it.

[Pedro]

Dude - end of the day, as Mr. U.D. said, it's your car, so your rules apply.

I think it's it's a death trap - my opinion, and like arseholes, everybody's got one.

You have to remember that Mr. MOT Tester might take a dim view of your "modifications" though - so expect that at least.

[encino]

I was going to show my friend, who was the guy you bought the car from, a few pics of how it looks now but I've just remembered that he has a dicky heart so I won't bother. 

[Land-Barge]

Looks great mate ignore the haters, comeon guys he hasn't just cut the spring he made up proper spring cups so as long as the springs properly supported and doesn't fall out Mr MOT should be happy, and it's a Carlton estate not a Formula 1 car

[Pedro]

Looks great mate ignore the haters, comeon guys he hasn't just cut the spring he made up proper spring cups so as long as the springs properly supported and doesn't fall out Mr MOT should be happy, and it's a Carlton estate not a Formula 1 car

And Formula 1 cars are not allowed on the roads...........for other people's safety.

[carlton_mad]

if the spring is INCOMPLETE it should fail doesn't matter how it is secured and a cut spring is incomplete!!

[Pedro]

Looks great mate ignore the haters, comeon guys he hasn't just cut the spring he made up proper spring cups so as long as the springs properly supported and doesn't fall out Mr MOT should be happy, and it's a Carlton estate not a Formula 1 car

As he says, and I quote: Dropped the back down a bit by cutting the springs. Had to do a bit of fab work to do it because of the pig tails. I found some old spring cups in the scrap pile (off E30 325i front struts I think) which were nearly the right size. A bit of hammering later and they were the right size. I then cut the bottom off the springs and ground the end flat. By unbolting the rear shocker, I could then put the spring in the cup on top of the trailing arm, then jack the hub up till the spring was located at the top. I then put the spring cup at the right angle, hit it with the melty stick and welded a couple of strengtheners in."

Cutting and grinding springs then hammering spring cups.
Alot of the temper has now been taken out of the spring, thereby making it softer. This means the dampers will have to work harder and will fail alot sooner than expected. And the spring could actually break. Nice work.

Hammering a spring cup - again, it will be regarded as 'old metal', which (in this case) will be work hardened, then it's just been hammered into a shape that it was not meant to be, it's supporting summat like 2 tonnes of a machine capable of travelling at 100mph. Doesn't bear thinking about as to what could happen.

So that's the metallurgy bits briefly looked at.

The suspension geometry next then.
So car makers  - as Mr. U.D. rightly pointed out - spend millions of dollars designing, redefining, making safer and generally finding a compromise so everyone's happy (in the main). Then the springs are shortened - by way over the industry recommended rule of thumb, which is 30-35mm. The reason this rule of thumb is there, is because a car's suspension can settle over time as the springs soften. Go beyond this and again, the standard dampers have to work harder - being required to do things they're not designed or built to do, the whole geometry (toe, camber, castor and Ackermann Angle in some cases) can end up waaaay out, the bushings are under alot more stress, the only component NOT to suffer - indeed, benefit from all this "work" is the anti-roll bar.

That's before we look at the handling aspects - which include easier to tramline, therefore harder to control, harder steering putting the whole power steering system under more strain...I've seen blown seals on a Saxo ( I think it was)cos it was lowered 60mm.

I wonder why race and rally cars need thousands spending on their suspension set-ups?
Perhaps they too should cut coils out of their springs?

As I said, the car in question looks cool - I really do like the look of it - but I seriously hope it doesn't come at a terrible cost.

Nuff said from me.

[Alex_FC]

Alot of the temper has now been taken out of the spring, thereby making it softer. This means the dampers will have to work harder and will fail alot sooner than expected.

Wrong, dont talk Engineering unless you know what it is your talking about.

[stealthstylz]

I do hope that you don't get caught up in any type of accident while your car has these chopped suspension springs Stealthstylz because if you do I'm sure you'll end up deep in the sticky brown stuff coz this kind of modification is just the excuse that any insurance company needs do declare their cover null and void.

JM2PW!

I told the insurance company and its on my policy as that so shouldn't be a problem.

Alot of the temper has now been taken out of the spring, thereby making it softer. This means the dampers will have to work harder and will fail alot sooner than expected. And the spring could actually break. Nice work.

Thats about as far from the truth as possible. Cut springs get stiffer as to calculate spring rate the forumla divides by the number of active coils. If you reduce the number of active coils then the stiffness of the spring will be higher. The only way springs lose their temper is through heat. I cut them with a 1mm slitting disk which produces very little heat.

Hammering a spring cup - again, it will be regarded as 'old metal', which (in this case) will be work hardened, then it's just been hammered into a shape that it was not meant to be, it's supporting summat like 2 tonnes of a machine capable of travelling at 100mph. Doesn't bear thinking about as to what could happen.

I stretched the vertical lip out by about 1mm so the spring was a snug fit in the cup. I could have left it as the spring did fit but wanted to be sure that it would stay seated

The car handles fine. A million times better than it did when it was standard anyway it was awful. The rear shocks have about 4" of compression left which is plenty.

if the spring is INCOMPLETE it should fail doesn't matter how it is secured and a cut spring is incomplete!!

How would you define incomplete? What is a "complete" spring. As I said they don't grow on trees as long as they're the same side to side they can't say anything. There's actually not rule that they should remain seated when the car is jacked up. The rule states that the spring should re-seat without external help which mine do.

The only thing I need to do is put the rubber damper thing on top of the rear springs as I forgot 

Matt

[flash911]

I think this is getting a bit heated !!! and NOT the first post to do so in the last 4/6 weeks 

[stealthstylz]

It's OK can't beat a bit of heated argument its not as if we're making personal remarks or whatever.

Matt

[8valver]

Well id say its been done as safely as possible, ie making the spring cups, not putting lots of heat into the spring, and realistically a few coils shouldnt make a massive difference. I mean i know some of the e30 boys run about 1/2 the rear pigtails without any kind of mods to the trailing arms, id say that was infinitley more sketchy.

As far as deviating from the 'optimum setup' goes, what gm decided was 'optimum' for the car might not be what stealthstylz thinks is 'optimum', ok the dampers arent quite matched, but again, its only a couple of coils missing, not half a spring.

all imo, of course

[stealthstylz]

GM didn't decide on the optimum setup by a long way. The stock suspension setup is a massive comprimise between handling, comfort, maximising interior space, ground clearance etc.

Anybody who thinks that manufacturer suspension setups are the optimum design are frankly deluded.

Matt

[Alex_FC]

GM didn't decide on the optimum setup by a long way. The stock suspension setup is a massive comprimise between handling, comfort, maximising interior space, ground clearance etc.

Anybody who thinks that manufacturer suspension setups are the optimum design are frankly deluded.

Matt

Yeah you are totally correct, life is always a compromise, for example sexy girlfriend - bad personality, fat girlfriend - great personality. So you go for the girl thats an all rounder.

So the same goes for suspension, ok generally but not great in any one area.

But that comprimise you speak off was developed, simulated, tested and validated. To ensure that the damper was matched to the spring rate. (The optimum combination of spring and damper, NOT the optimum setup).

Just to be clear, drive your uber cool car and dont worry, The worst case the road surface roughness is the same frequency at a given speed as the natural frequency of your car suspension setup and it shakes to bits, lol. Not likely

Just make sure the damper doesn't bottom out, that is bad.

[U.D. - Omega DTM Rep]

Just to be clear, drive your uber cool car and dont worry, The worst case the road surface roughness is the same frequency at a given speed as the natural frequency of your car suspension setup and it shakes to bits, lol. Not likely

Really Alex_FC? Not likely eh?? Ok, I wonder why I've seen so many of our cars over the years meet a premature end thanks to multiple stress cracks and popped factory spot welds....













Still, I am in the deluded camp regarding this type of modification. Keep up the good work there Stealthstylz. To save on any future harsh comments or nasty feelings developing, this will be my last post in this topic regarding your kwality suspension set up.

All the best,

U.D.

[Pedro]

Alot of the temper has now been taken out of the spring, thereby making it softer. This means the dampers will have to work harder and will fail alot sooner than expected.

Wrong, dont talk Engineering unless you know what it is your talking about.

Thanks - I'll remember that.

[Pedro]

I must apologise for saying the springs would be softer - I am wrong there.

My other comments are still valid, though.

Please, Alex FC, don't tell me what I - or anyone else - can or cannot post on here. ass I said, it's not my car, I think it looks good, but I also think it's dangerous - MY VIEW of which I am entitled.

Of course, I know nothing of Mechanical or Fabrication Engineering - it's what I've been doing for the best part of 30 years!

[Alex_FC]

I must apologise for saying the springs would be softer - I am wrong there.

My other comments are still valid, though.

Please, Alex FC, don't tell me what I - or anyone else - can or cannot post on here. ass I said, it's not my car, I think it looks good, but I also think it's dangerous - MY VIEW of which I am entitled.

Of course, I know nothing of Mechanical or Fabrication Engineering - it's what I've been doing for the best part of 30 years!

Sorry Pedro, I feel bad now. I have been put in my newbie place

[stealthstylz]

Yeah we simulated hitting the resonant frequency of the car at uni on a 4 post rig, the results were hilarious. As I mentioned there is about 4" of compression travel left on the damper, and the spring is plenty stiff enough to ensure that it will never hit the bottom of its travel (unless I launch it off a bridge or something daft)

I'll keep an eye on the stress cracks. Can't really call it a premature end if the shell is cracking its just shit design.

I'll try and take some vids of it driving. It handles like a go cart lol.

Matt

[Pedro]

I must apologise for saying the springs would be softer - I am wrong there.

My other comments are still valid, though.

Please, Alex FC, don't tell me what I - or anyone else - can or cannot post on here. ass I said, it's not my car, I think it looks good, but I also think it's dangerous - MY VIEW of which I am entitled.

Of course, I know nothing of Mechanical or Fabrication Engineering - it's what I've been doing for the best part of 30 years!

Sorry Pedro, I feel bad now. I have been put in my newbie place

Don't feel bad - how about enlightened?

[Pedro]

Yeah we simulated hitting the resonant frequency of the car at uni on a 4 post rig, the results were hilarious. As I mentioned there is about 4" of compression travel left on the damper, and the spring is plenty stiff enough to ensure that it will never hit the bottom of its travel (unless I launch it off a bridge or something daft)

I'll keep an eye on the stress cracks. Can't really call it a premature end if the shell is cracking its just shit design.

I'll try and take some vids of it driving. It handles like a go cart lol.

Matt

I have seen the results of that happening on a Rover 400 (IIRC). I know it could be a different set up to the Carlton
Humpback bridge, too fast, rear (cut down) springs fell out, guy in hospital for a long time and the car was a real mess - basically it bounced into a house, narrowly missing busy road junction at school finishing time.
I saw the car before the fire tender got there and helped the guy top stay calm before the paramedics arrived.


I don't want to frighten people with the above, but it happened in a village called Strensall, near York about 12 years ago.

As this is a free, public forum (which I have the honour of moderating), I feel that as much information that everyone can provide can help others to make an informed decision.

[Jimmy]

i had a right laugh reading this post, ha ha , all things aside, i love the look, and love the rusty madmax black colour, only works on estates too

[stealthstylz]

I have seen the results of that happening on a Rover 400 (IIRC). I know it could be a different set up to the Carlton
Humpback bridge, too fast, rear (cut down) springs fell out, guy in hospital for a long time and the car was a real mess - basically it bounced into a house, narrowly missing busy road junction at school finishing time.
I saw the car before the fire tender got there and helped the guy top stay calm before the paramedics arrived.

My springs shouldn't fall out thats why I welded the spring cups in. I launched the Carlton off a hump back bridge at 90mph (didn't realise it was there) when the front was lowered but not the rear. Was a bit hairy but luckily I kept it in a straight line and just slightly grazed the kerb when I landed.

Matt

[Alex_FC]

Are your wheels 15inch Senator Wheels?

[stealthstylz]

Nope they're 17x7.5 (front) and 17x8.5 (rear) BBS split rims. They're ET41 but i've got 25mm adaptors in there. They're literally the perfect offset I've got about 3mm clearance to the rear arches but it doesn't touch.

Matt