En route to my first ever hillclimb this morning (which just didn't happen - more elsewhere), I had the mother and father of a moment on the road.
I was leaving a roundabout and had some left lock on the steering to straighten the car up and was just putting the smallest amount of power on.
The back of the car started sliding away out. This is at 30mph in 3rd gear and 50% throttle. I eased off 'a bit' to help it come back in and it swung the other way - naturally. Unfortunately it swung right up the kerb and onto the grass. At this point I was travelling sideways and into a lamp post. God only knows how, but I avoided the lamp post and got it straight again and managed to stop.

The thing that's really freaking me out was that it was so utterly easy to provoke.
Now, I would be the first one to admit that my rear suspension has issues.
One issue specifically...

It has positive camber.

Not a lot, but it's still there. Maybe a degree or two, but it's obviously totally wrong - I am thinking that I need something more like 1.5 to 2 degrees of negative camber.

Any thought on this in light of the incident I had this morning. I'm thinking that instead of the car rolling onto the tyre it is currently rolloing off the tyre - lessening an already small footprint and hence all the grip just dissapears.

The thoughts of the qualified would be most welcome here, because I really think I want to modify my bottom wishbones to get this sorted out ASAP.

The back could have stepped away for any number of reasons. Was it wet? Did you simply over power the tires?

You spun because you lifted off the throttle. You needed traction in the rear. When you lifted, you transfered all the weight to the front tire--exactly where yoyu didn't want them.

Probably should have stayed on the gas a bit longer and rod it out...

Chris

In no specific order.

Yes - it was wet, and the exit of a roundabout so potentially diesel on that bit.
Power wise, I gave it half throttle at about 3000rpm in third gear. That doesn't amount to very much on a 1.4 K series

I know I should have kept power on, but all I did was modulate power down to about 25% and I was gone. Didn't close the throttle. I've actually had the car out of shape in the dry before and it was fine, but on this occasion it was just gone.

Any road up, I think I need a 4 wheel geo check before I start to make any further comment.

**Further thoughts**

On the basis that handling when turning right is much more benign than when going left, and having had a highly technical right good look at it, I reckon that I have positive camber on the OSR wheel and that the NSR is actually ok.
It's highly possible that my rear subframe has had some form of traumatic event in the past
Anyway - have a looky at these pics and cast your eye along the flank and wheel cambers etc...







[Edited on 1/5/05 by zilspeed]

[Edited on 1/5/05 by zilspeed]

Toe-in is worth checking on the Davrians I ran 1/16" to 1/8" toe-in on rear.

You were turning left out of the roundabout. Right? OK the OSR wheel has the pos camber. The NSR would be unweighted thus no traction, all the weight transfer is to the OSR which, since loaded, is runing on the outside of the tire with no traction, start to slip a little so you let off the skinney pedal and really unload the back end which really makes it want to swap ends.

You are right about the camber, you should be running - 1.5 deg and a touch of toe in...But that is just my opinion based on years of driving too fast.

D.

Glad you didn't mess up any paint on the car, the pucker mark in the seat will go away.

Yep - I let off the gas. Not a lot, but I let off the gas

Having since studied the rear suspension in a bit more detail, it is clear that the NSR bottom ball joint is original and the OSR is a replacement. It is entirely possible that this is a factor due to the way that the joint is secured to the wishbone.
I'm going to fit a new joint and give it a bit of a tweak while I'm at it

I reckon it'll really dig in and grip at the back once I've done that.
Honest.

PS. When I let off the gas it was already an accident

Are the joints handed, can you swap them over to see if they alter the camber on the other side or if the subframe is bent?

Pete

The joint come from the factory riveted to the wishbone. When they need replaced, you grind out the rivets and bolt in a new one. I have both arrangements on the car. The suspect offside one is the one that is bolted in and has obviousy been replaced.
The bent subframe idea isn't lost on me, or bent wishbone for that matter. All it would take is a smack to the bottom of the wheel, following a slide.
If the frame or wishbone aren't bent, I will slot the mounting holes in the wishbone and do likewise with the new joint. This should give me enough adjustment to get it right.

Zil,

Was it a newly surfaced road?

There has been a few issues regarding the new anti-skid road surfaces being 'like glass' when wet. I can't recall the guy on Radio 5 who spoke about it... but he was a well experienced traffic plod who stated that to stop in the dry at a certain speed took 30 feet. In the wet he would have expected to take twice this at he same speed it took 10 times this. He could not explain it but he said that in Ireland they tried this new surface and his theory was proved so they took it all back up again... and paid out compensation to those affected.

Perhaps someone from Ireland could verify this... Alistair??

Positive camber on rear wheels promotes oversteer (and on front wheels promotes understeer)

If the road was greasy and the tyres where overwhelmed by cornering and power then you will lose grip. Remeber that Morris Minors could be power slid at 20 MPH.

Thanks all, for confirming what I thought anyway.

I know what I'm going to do now

. Find the best setting by slotting the holes then weld washers on the wishbone to make sure it stays put if you're using it for hillclimbs just in case it gets nudged back.

I will certainly be marking the existing and new positions and intend using some of those K nuts that bite in to help positive location. Once I've established a setup that I like, I will most likely plug up the holes and redrill. There's plenty meat on the wishbone and the joint for doing this.
5mm of a slot extension on each obviously gives me 10mm total travel. That would show up as quit a bit more on the wheel rim.

a drop of diesel on the road will cause that

I had thought of that as well, but it still doesn't feel planted at all at the back.

What confuses me is that the previous owner must have been completely insensitive to this or a bit of a hero to drive around it.

Zil,

If you want it set up after your changes, gimme a call.

Steve

That would be magnificent.

Would this be in your flat floor race facility ?

P.S. I have various numbers to use in setting up the geometry. I will bring them with me.

You are indeed a great man.

Hi Zil,

I have had my K3 for 10 months now and am trying to solve/sort this very same bad behaviour.
The Hydragas suspension is linked corner to corner (i.e. front left to rear right) so when you induce a weight shift from front to rear going around corners it gets hairy as you know. Part of the problem is down to lack of damping/ anti-roll/worn subframe bushes. My jobs for the summer are fitting shocks/exploring anti-roll bars (probably not enough room though) and fitting poly bushes in the subframe mounts. My car has had a number of 4 wheel trackings done before I bought it and I think that the tracking "goes out" when it leaves the garage due to the bushes etc.
Also make sure that your ball joints etc are for the GTI/GTa as the geometry is different to that of a normal metro.
Good luck and if you fit a waterproof cover to your seat then you can always pressure wash it after the wild moments.


regards

Steve

Oops - missed this.

It's been a wee while now, but negative camber and toe in have helped immensely with the security of the handling.

Now firmly ensconced in a top end rebuild - looking for a touch of extra grunt as well. All good fun.

P.S. have checked your pics. Your car sits much higher at the back than mine.

Have you fiddled with ride height at all ?

[Edited on 16/6/05 by zilspeed]