Alignment/Stance/Handling

[jamesdi]

Hi all,

I have a 2003 pre-facelift Z4 Roadster 3.0i.

2 years ago I replaced all bushes and suspension components.

Front axle:
Meyle strut top mounts, yellow Koni shock absorbers with blue H&R springs, Meyle HD droplinks, Meyle HD tie rod assemblies, Meyle HD lower control arms, Powerflex lower control arm bushes (ones with the black aluminium sleeving inserts) and Meyle engine mounts.

Rear axle:
Lemforder strut top mounts, yellow Koni dampers, blue H&R springs, Powerflex upper arm inner and outer bushes, Powerflex adjustable lower camber control arms with powerflex inner and outer bushes, Powerflex rear trailing arm bushes, Powerflex differential bushes (all 3 of them), Powerflex subframe bushes (all 4 of them).

I then got the car Hunter aligned by a professional who is extremely knowledgeable. I asked for it to be aligned on Z4M settings, as this was recommended by many on this forum but no real reason/evidence was given as to why this was better than the standard 3.0i Z4 settings...

The car feels "tight", drives straight, handles and turns well at speed no question about it.

My only concern is that this new alignment setting which I got done 2 years ago, gives the car a very different stance which I'm not too happy about. Before I had lots of negative rear camber which really made the car look well planted and wide - which I like, but obviously not good for tyres! I am also on 19 inch wheels and sometimes get a little rubbing on the rear (I didn't have this before obviously as the wheels had more negative camber). The front also now sits alot higher and makes the car look a bit "goofy".

This has got me thinking whether it was even a good idea to have the car aligned to Z4M settings? The Z4M has different subframes and arms and different hub offsets, so surely this wouldn't work well with the standard Z4's?

My question is, what is the max negative cambers I can run without affecting driveability/functionality badly? I like how it handles just now, but wondering if adjustments can be made to help with the stance of the car...

I also note that there is A LOT of road noise in the cabin, to the point it gives me a headache at times - I presume this is due to all the Powerflex bushes? I have installed double layer of sound deadening behind the door cards, boot lining and rear middle sections, but still noisy.

I am planning on replacing both rear wheel bearings and taking the dampers off to adjust them to soft (currently set to mid). I will then get the car aligned again.

What are the best settings to go for and what's the max negative camber I can run? How does toe affect the cars handling? I have seen some members on this forum recommend zero toe all round. What's the reason for this?

I can upload a picture later of the printouts of the alignment numbers if that helps?

Any advice is greatly appreciated

 

[LemonConnoisseur]

Sounds like you've made all the correct mods to make the car a capable B-road machine, but replacing rubber bushes with polybushes is going to increase the NVH (Noise, Vibration, and Harshness), so it's a trade-off. Harder bushes allow the suspension components to work more effectively, as the components between the springs and dampers aren't flexing and distorting, as a rubber bush will.

Toe is the direction that the wheel is pointing in when straight. Toe out means that each wheel will be oriented slightly away from a central line, toe in means the opposite. Neutral toe (0) is generally used for a road car because it means that it's not dragging the tyres across the road as you're driving straight (accelerating the wear), will promote the vehicle to track in a straight line with minimal steering input, and also will handle predictably under normal driving conditions.
As for toe settings, it really depends on what you want out of the car. If you want a sharper turn in and assistance from the tyres under braking, then you can run a touch of toe out at the front. The trade-off, however, is that the car may feel less stable in a straight line at high speed as each wheel is technically pointing away from eachother, and also the tyre wear on the inside edge. It will also heat up the inside of the tyre, which is another contributor to wear.

Camber doesn't usually eat tyres, toe does.
Again, it depends what you want from the car with regard to camber settings. I personally like to run a reasonable amount of negative camber at the front because I enjoy the benefits it gives when driving the car on a track. When you corner, the car will roll and reduce the amount of available contact from the tyre onto the surface (contact patch). By increasing the amount of negative camber, when the car starts to roll, the contact patch then becomes larger on the outside tyre, as the camber is compensating for the decrease in contact patch that you would usually expect. There is obviously a practical limit as to how much camber to run.
I'd also, again personal preference, run less camber on the rear than the front because of camber gain and the design of the BMW rear suspension (semi-trailing arm). When the rear of the car "squats" under power, it naturally introduces more camber anyway.
As for trade-offs, camber does increase tyre wear on the inside edge too. It can also make the car feel slightly more skittish on the road, as I find it tends to wander and hunt tramlines a bit more.

I can't say for sure why people opt with the CSL alignment, but I can only assume it's to make the car more stable and give it more grip whilst cornering at higher speeds, and also help with the understeer that BMWs naturally have (staggered wheels, heavy engine over the front axle).

Hope that helps a bit

 

[MikeyH]

Thank you, I enjoyed reading you explanation, it made everything very clear to me, I have always wondered about what the different setting do.

 

[Mr Tidy]

When I had some bushes replaced on my previous Coupe my Indy didn't recommend polybushes for a road car as they would make it too harsh. As he is ex-Sytner and has a couple of race cars I went with standard ones!

After changing the ride height, removing spacers and changing wheel sizes on my MC I took it to the same guy for a 4 wheel alignment and had it done to E46 M3 CSL settings and it totally transformed how it drives. Way less understeer and a more playful rear end - lovely.

I'm not sure how CSL settings would work on your car but I hope you can find some settings that work.

 

[plenty]

Standard Z4M rear camber settings are 1 degrees 50 minutes or close to 2 degrees, while the non-///M 3.0 runs 2 minutes 50 degrees or almost 3 degrees of rear camber as standard. So they already run a lot of camber. You have adjustable camber arms on the rear and if you want you could go to 3 or even 4 degrees which will still feel 'normal' on the road.

More rear toe-in will make the car feel more stable in a straight line but less eager to turn, whereas less toe-in does the opposite, i.e. car will feel more nervous but quicker to turn. So it's up to you to decide based on how you like the car to drive. OEM alignment specifies a lot of toe-in which is safer for novice drivers as it lowers the risk of sudden and unexpected oversteer.

Reducing rear toe to 2 minutes (CSL settings) or even zero is considered more enjoyable by confident drivers as it makes the car more pointy and responsive. If you are running 3 or more degrees of rear camber you do not also need lots of toe in as the camber will help plant the rear in fast cornering. Minimising toe in if you are running lots of camber will also help save your tyres, as both running both camber and toe is a surefire way to destroy your inner edges quickly if you drive in straight lines for any distance.

Ride height is determined by your struts and springs and is unrelated to alignment settings.