Z4M getting some recognition

[plenty]

BC coilovers or Bilstein/Eibach kit: £900 (can look out for people on here selling lightly used or unused which come up fairly regularly)

Rear trailing arm bushes (RTABs): £75
Front wishbones and ball joints: £150
Lollipop bushes: £80

You'd might as well replace a few more bushes and the tie rods while you're in there, but the above alone should make a huge difference. It's a simple job that does not require a specialist. Find a competent mechanic with a reasonable hourly rate and you can likely get everything fitted for £300-400. Throw in another £80 for an alignment and you're looking at £1,500-£1,600 in total.

I personally would replace 15-year-old rubber bushes regardless of mileage as it's inexpensive to do so, especially if you're not happy with the way the car drives. I'm not a fan of poly bushes for a road car but I did opt for Powerflex for the the RTABs simply because they were much easier for me to fit (the OEM rubber items require a specific pre-loading install method). If you do go with rubber for the RTABs, make sure to install aftermarket limiters. Lots of info online on this.

[maupineda]

OK that sounds easy but v costly. At least for me.

Is there any benefit to be had from firmer bushes like selective use of poly? My car is low miles at about 40k but probably needs new bushes. On the non m z3 I added poly rear beam bushes and z3m front control arm lolly pops along with new bilsteins and the rest new factory rubber bushes but that car is 10 years older. It made an amazing difference along with a larger rear sway bar from z3 3.0 coupe.

Do you think a 2007m with 40k on the clock would need new bushes? If so where would it be appropriate to use poly. I understand z3s but am a newbie when it comes to z4ms

I think it all depends on weather conditions, my car is 82k kms and 15 years old, yet the bushings are tight, but is a car that has not seen a lot of rain, heat, and salt. my suspension is tight as a drum and some of the bushings I have changed, I did more for upgrading or renewal. so, review, inspect, and assess. going poly will just make the car unnecessarily stiff without much benefit. Keep the OE suspension and refresh what needs to. The car is stiff as is, and adding uprated shocks and springs will make it worse. I have coil overs and the car is indeed stiffer and less compliant from an NVH standpoint. but that is the price for "sportier" suspension. if I was to do it again, I would just do B6 shocks and keep stock springs, then refresh worn-out bushings, and do a custom alignment and put decent rubber.

[Sajk]

Thanks for the advice.

[Mr Tidy]

My car came fitted with H & R coil-overs that were only a few months old so I've kept them but they are really firm and only adjust for ride height. If/when they need changing I'd probably go for OE or if I was feeling flush KWs with adjustable compression and rebound!

When I needed new engine mounts Ross at RBM (bowser134 on here) recommended OE rather than Vibra-Technics for a road car - same with poly-bushes.

After raising the ride height, removing spacers and going back to 18" wheels from 19s I had a 4 wheel alignment last year to E46 M3 CSL settings and my car was transformed.

[plenty]

The OEM spring rates are all wrong.

Due to the low ride height the progressive springs operate close to their end rates much of the time. The result is a strange combination of the front end being too soft, contributing to understeer, poor turn-in and a general woolly feeling, while the rear end is too hard and is under-damped, which is why the primary ride on OEM suspension is so poor.

A rear spring rate that is so significantly stiffer than the front creates a sensation of the front and rear being disconnected, as if you are driving halves of two different cars that have been spliced together.

Most aftermarket suspension fixes this. To use BC coilovers as an example, the default springs are linear and 335 lbs/in F and 560 lbs/in R (you can specify stiffer fronts if you wish). The stiffer front springs tighten up the feel considerably, while the rears are actually softer than OEM which means a more compliant ride than OEM and a more planted rear. And the F/R rates are much more closely matched leading to a much more cohesive drive.

[PDJ]

I personally don’t agree with the comments about polly bushes making the car harsher.
My take on it is. The OEM, polly bush or even fully rose jointed (I did all 3 types on my Westfield) is the bush or bearing, it is just a pivot point for the suspension to move around and a small amount of movement at that.
The harsh ride will come from the shock absorbers and the springs.
If you take it to extremes and say the spring is that stiff it does not compress, it is not the bearing making the car harsh, now if you go the other way and make the spring very soft the car is soft and floaty.
The shock absorber takes the shock out of the movement and controls the rebound the spring has trying to return the energy it gained in compression
If anyone want a ride in my fully polly bushed Z4M to compare just get in touch car is still used as I have no garage at the moment but as soon as the salt is on the roads it will be staying put just outside where I am renting while I have a house built.

[plenty]

The harsh ride will come from the shock absorbers and the springs.

There are two types of ride: primary and secondary.

Primary ride is the car's ability to cope with undulating terrain, and is indeed a function of compression and rebound, affected by spring rates, damping and geometry but not by bushes. In fact stiffer bushes can improve primary ride in some circumstances, e.g. worn rubber RTABs flexing on compression and causing unwanted lateral movement of the rear axle leading to the feeling of a "loose" rear end especially over bumpy ground.

Secondary ride is the car's transmission of NVH and this is indeed affected by using harder bushes. So using poly bushes or rose joints won't affect primary ride, and in fact will make the car more precise and responsive to driver inputs, but it will degrade secondary ride by adding NVH.

[maupineda]

My car came fitted with H & R coil-overs that were only a few months old so I've kept them but they are really firm and only adjust for ride height. If/when they need changing I'd probably go for OE or if I was feeling flush KWs with adjustable compression and rebound!

When I needed new engine mounts Ross at RBM (bowser134 on here) recommended OE rather than Vibra-Technics for a road car - same with poly-bushes.

After raising the ride height, removing spacers and going back to 18" wheels from 19s I had a 4 wheel alignment last year to E46 M3 CSL settings and my car was transformed.

The H&R coils are seriously flawed from the get go, I had to modify springs and bumps stop to make a decent kit out of them

The main issues are:

- The front bump stops are toooo long, 70mm. I cut them down to 45mm
- their springs are too low, this makes the ride absolutely crap, you ride on the stops all the time, so with stiffer springs, plus riding on stops, you end with a very crashy ride

The above could be fixed, however, the dampers are too stiff and have close to 60lb of gas force, all these give you have a rock hard suspension (not fun).

To fix the first two issues I did the following

FRONT
- change springs to swift springs, this required new threaded perches from Öhlins. I chose 225 lb/in (all this is cheap if you DIY)
- cuts stops to 45mm

REAR
- used B8 shocks from non M, they are still valved very stiff, also have much gas pressure, but overall allow for shortening the rear stop and reduce droop which is needed with shorter springs, they are shorter than H&R coils shocks and OE.
- used barrel type springs from TCK, I chose 600 lb/in

With the above changes made the car ride much better and can now can round sharp bumps well to some extend, and the car is much less crashy and body control is superb.

The one thing I cannot fix without spending too much money is gas pressure in the dampers, but maybe 30-40 lb of gas force would improve things much further. I think 30lb of gas would be best for road.

Mexican roads are crap, so all the above was needed to coupe with our awful roads.

The issue was not much spring stiffness, but damping, plus ride height, plus bump stop length.

My setup above gives me 10mm more of suspension travel before touching the stops, so I have more effective suspension travel vs OEM, and the same overall travel until bump stops are solid blocks.

The above plus CSL alignment makes the car go on as in on rails up to 7-8 10ths, though the one thing the CSL alignment augmented is tram lining, so for poor and unleveled roads it needs some toe.

[Mr Tidy]

Many thanks for your detailed response.

You're right about the ride on the H & Rs, even with some added sidewall on the 18s mine is still very firm. I think I need to try one with a different suspension set-up to get an on-road comparison.