Z3 2.8 suspension upgrade

Hi & a late happy new year to you z3 owners !! Could anybody give me some advises regarding a suspension upgrade ?? As my z doesn't seem to handle great or should I say it seems sluggish into corners & very rollie pollie !! Body roll , it's always done since owning the beast and as its passed every single MOT & even commented on how good condition it's in for a 99 V ! So I'm thinking of biting the bullet & upgrading to Koni STR.T with HR springs or Koni sports adjustables with HR springs ! Both sets are mid line cost wise as carnt afford to go mad any ideas about my choices and would it be advisable !!! Silver Z

Hi ...can you say what you are trying to achieve with the suspension change in order to offer the best advice....eg road use possible track use etc...cheers

My Z3 is a 1998 2.8, and has never been tail-happy or suffered from body roll.  I have owned it from 12000 miles, and it has now covered over 120,000 miles.  I have carried out various susopension modifications, mainly as components have deteriortated - detailed in 'Body Stiffening on a Z3,' and  'Subtley Stiffening a Z3,' which are both in the 'How To' section of this forum - they were published in the magazine a couple of years ago.

After all these years new dampers would probablly not go amiss, as the MoT just looks for leakages - it does not check the damper performance.  A soft damper, or a  'slack' damper, with free travel before damping takes place may well be the cause of your body roll.

My choice was Bilstien Sprintline dampers with Eibach front springs (about 30 mm lower and so a bit more negative camber) and the standard rear springs (as I want to be able to carry a passenger and luggage) with E46 strut mounts, Powerflex wishbone and ARB bushes, and PVC stiffening pieces inside the rear cross member mounting bushes.  I also replaced the rubber spring seating rings and rear damper mounts - a new improved type is now available, as used for all cars.

The Bilstiens have massive damper rods (30 mm diameter) so they also make a large contribution to increasing the rigidity of the front suspension.

The springs which come with the Bilstiens (in the UK) are cheap rubbish, being too short at the back, and apparently made of chocolate, as they settle at an alarming rate.  Daughter used them on her E36 Compact, and after a year the coils began to split along the middle - avoid cheap springs like the plague.

I have a Hamann strut brace, which also makes a slight improvement in initial steering respose, but nowhere near the huge improvement to handling some people claim - I think they find the improvement is in proportion to the amount of polished aluminium!  I will buy a Strong Strut steel strut brace soon, which being straight is a far better design.

I also use a 17 mm rear ARB (the standard is 14 mm) which sharpens the steering a little, and a 340 mm RAID steering wheel, which being smaller than standard also makes the steering a little quicker.

Unless you value fashion over function, avoid excessive lowering, particularly if you later wish to fit Strong-Strut's Butt Strut and Body Brace, which make more difference that all the lowering in the world - and also protects the car floor from speed bumps and sharp ramps!

The ARB bushes deteriorate to allow more 'wind up' movement before the ARB takes effect, and can be obtained fom Powerflex in any size - but make sure you have bushes for a Z3/E36 and not the E30, or they have to be modified a little to fit securely into the clamps.

With the Bilstien/Eibach/Strong Strut/Powerflex/Hamann setup I find that the car has no  body roll, a decent ride, and adequate ground clearance.  Handling is basically neutral, with a hint of initial understeer until slight power is applied.  The back end remains planted on the road to higher levels than I have courage to try!

Rear tyre life is about 5000 miles more due to the Strong Strut braces, as the cross member does not move around, so altering the rear wheel toe-in.

Apart from the springs and dampers this work can be done in bits and pieces, which also allows you to assess the changes each piece makes.

After a bit of experimentation I found that 2.4 bar in all the tyres (Falken FK-452) was about the best - it reduces understeer, improves steering response and 'feel,' and improves grip a little. 

Talking of tyres, I still buy my tyres and have the wheels balanced  at Pro-Tyre of Plymouth, as they are far cheaper than in France, where they cannot balance an 8.5 inch rim!

The Bilstiens have now  seen about 40,000 miles, yet when the car has its Control Technigue (2-yearly French MoT) when the damper performance is checked, the fronts are exactly matched, and the rear vary by 1% - it's worth buying good parts if you intend to keep the car, and after 12 years of ownership I have no intention of selling the Red Zed!


Edited by Mike Fishwick - 12 Jan 2013 at 12:58pm

The trailing arm bushes are certainly neglected, simply because they are so difficult to change in situ - it's the same with the rear cross member bushes.  Thankfully, the rear suspension bushes are a lot better design that those on the rear end of the front wishbones.