Where's my camber??!!!

[ZetaTre]

I went for an alignment at Firestone on Sunday: front toe was way out (almost 1 deg inward on both wheels... this actually stinks like the dealer who sold the car doing a quick fix on a problem we had when we bought the Z), rear camber is down to about 1 deg on both wheels (from the 2 deg and some change for the non-sport suspensions) while the toe on the rear-right is too much in (I think that's why after the front toe was adjusted to specs the car has a slight pull to the right)
I was surprised to know that on the Z4 camber and toe both front and rear are adjustable. But you need a special tool for it. The guys at Firestone told me that if I go there with the tool they will be able to adjust the rear as well.
Did any of you guys have any experience with this?

 

[Curtis]

It sounds to me like you still have a dodgy alignment specialist! The toe and camber are adjustable on the front and rear ( although the front camber is not done by conventional means ) but you don't need and special tools to do any of it.

The front toe is adjusted in the ususal manner by lenthening or shortening the steering arms. I generally set mine at 1 degree toe out.

The front camber is adjusted by removing the dowel in the upper strut mounts and pushing the struts inboard. You can gain around 1.5 degrees of negative camber using this method but any more than this will require the use of shims. 1.5 degrees neg camber is perfect for fast road use though.

Rear toe is adjustable by repositioning the rear trailing arm front mounts which are fitted using elongated mounting holes. I usualy set mine at 1 degree toe in for road use.

Rear camber is adjusted by rotating the eccentric bolt in the lower camber control arm. This bolt is intentionaly designed so that as you rotate it you move the lower hub mounting point in or out while the upper mounting point remains fixed, the result is that the hub tilts as you rotate the bolt. I think you'll find that 2 degrees negative is a bit excessive for road use. We rarely use extremes like that even on BMW race cars. I certainly don't use more than 1.5 degrees neg at the back for fast road use otherwise you just wear out the inner edge of your tyres and generally standard Z4's can't generate enough lateral load on the tyres for 2 degrees neg camber to become usefull. Mine is anything but standard but 1.5 degrees is still more than enough from my experience.

Check out the link below, the eccentric bolt is part 10 and the trailing arm mounts are part 17.

http://www.realoem.com/bmw/showparts.do?model=BT52&mospid=47797&btnr=33_1139&hg=33&fg=30

If your settings have moved you might want to check that your bushes and joints havn't worn out. They weren't very good in the first place and they wear out very quickly even under normal use. As I've mentioned in previous threads the geometry settings tend to shift around dramatically under driving conditions as the standard bushes are made of soft rubber and they flex under load so everything is a bit hit or miss unless you fit uprated parts.

 

[ZetaTre]

Thanks for your input, particularly on the rear camber. Maybe was the excessive tire wear experienced by the previous owner that asked to reduce the rear camber: on both wheel is a very similar number, so it could have been set that way on purpose.

There might be an easier procedure to adjust the rear. Problem is the TIS says a spacial tool is required and Firestone won't work on it unless I provide them with the special tool. I would guess that if they don't follow the manufacturer procedure they can be held responsible if something happen. I don't either wanna take it to another place since I already bought the lifetime alignment. I will upload pix of the procedure tonight.

It's funny you mention that a 2 deg rear camber is excessive: the sport setting with lower springs can go up to 3 deg. If interested I can post alignment setting recommended by BMW.

 

[Curtis]

It doesn't matter but thanks anyway. I know what BMW have stipulated but I also know it doesn't work! BMW's entire suggested geometry settings are a bit of a standing joke in the independant and racing community. It's as if they intentionally wanted the cars to handle well below their capability's.

I forgot to say, the special tool required is a spanner or wrench as it's called on your side of the pond. I suppose you could call that a special tool but it seems a bit over dramatic.

 

[ZetaTre]

I know what BMW have stipulated but I also know it doesn't work! BMW's entire suggested geometry settings are a bit of a standing joke in the independant and racing community. It's as if they intentionally wanted the cars to handle well below their capability's.

Could you elaborate a little more for the masses :tumbleweed:

 

[Curtis]

As with most aspects of a road car the geometry settings are a compromise between ride comfort, durability, safety and effectiveness however some of the standard settings used by or recommended by BMW greatly exceed the extreme limits that would ever be useful even under full race conditions. For example 3 degrees of rear negative camber. In the racing world it is common knowledge that BMW's do not benefit from extreme levels of neg rear camber but can benefit from quite large amounts of neg front camber. In normal road use you will find that 99% of the time you will be driving in a straight line or round gradual bends or turning at junctions at relatively slow speed. This means that 99% of the time your tyres are running on their inner edge because you've tilted them inwards at a 3 degree angle. This creates more problems than simply wearing out the inner edge of your tyres, it also means that the contact patch of the tyre on the road is greatly reduced which in turn means poorer braking, acceleration etc due to reduced traction. Neg camber comes into play under heavy cornering situations where the lateral G's will cause the tyre to flatten against the road creating maximum surface contact and therefore the best available traction. Again the problem of compromise comes into play, you can't set up a car to have the best of everything under all circumstances so you have to find a setting that will not become dangerous under any particular scenario but will provide the best the car can provide under a variety of situations. As I said earlier 3 degrees of negative rear camber exceeds the figure that I have ever seen used on the track and those cars can obviously generate a lot more lateral G's than a standard Z4. Because race cars create higher lateral G's they will flex the tyres to a higher degree and would therefore benefit more from higher levels of neg camber otherwise they will start running on the outer edges of the tyres under cornering followed by a sudden loss of traction. Having said that, the angle to which they are adjusted is nowhere near 3 degrees which is the figure suggested by BMW for day to day use in a road car. The highest setting I've ever come across is 2.5 degrees neg rear camber on a German DTM car.

This is a slightly over simplified description of the flaws in BMW's recommendations but I hope it helps explain why they should be taken with a pinch of salt.

 

[ZetaTre]

Thanks a lot!!! Great info.

Only thing I don't yet understand is why then BMW recommend such a high rear camber if, after all, the problems associated with it outweigh the benefits? Maybe is too much of a philosophical question, so I don't expect an answer.

 

[Curtis]

I've thought about it too and some of the answer might be due to their crappy standard bushes. As we discussed earlier neg cambers purpose is to allow for the flex in the tyres under lateral G's however there's more to it than that. As I said in the last post I over simplified things a bit! Anyway, on a standard BMW it's not just the tyres that flex, the suspension is all mounted using soft rubber bushes which flex very easily when any force is exerted on them and some of the geometry setting are in place to compensate for this. These bushes provide great ride comfort but contribute nothing to handling ability. What it actually means is that all your calculations and geometry settings are only good provided the car doesn't actually move! Once moving various forces are exerted on the steering and suspension from various angles under different situations which has the effect of moving the suspension within the rubber bushes and consequently changing the geometry settings. That's why race cars and even well sorted road cars will have all the soft rubber mounts replaced with more substantial items.

All this still doesn't explain why they would recommend 3 degrees neg rear camber as a standard daily driver setting. It seems more realistic that a setting of nearer zero degrees would be more suitable since a vast majority of the time the car will be running with the tyre flat to the ground while driving in a straight position or minimal variations from that position.

The best thing to do is work out what kind of use you personally will be using the car for and make your decisions based on that. Whatever happens I certainly wouldn't recommend anything more than 1.5 degrees of neg rear camber ( or front for that matter ) for normal road use and the rear setting is perfectly adequate for track days too. You might benefit from increasing the front neg camber to around 2.5 degrees neg for the track provided you have the means to do so such as shims or adjustable camber plates. Track settings are a whole different ballgame though so I better stick to the point!

 

[plowy]

Quite a deep topic Curtis that intrests me, for what you would call 'fast road' and a dozen track days a year, which about sums me up i think, what would you say the car would benefit from being set up like, secondly there is a motorsport place new me that does this with a four wheel laser thingy, would someone like that be capeable of achiving it do you think. ??

 

[Curtis]

Quite a deep topic Curtis that intrests me, for what you would call 'fast road' and a dozen track days a year, which about sums me up i think, what would you say the car would benefit from being set up like, secondly there is a motorsport place new me that does this with a four wheel laser thingy, would someone like that be capeable of achiving it do you think. ??

It's quite difficult to come up with a generic set up because some settings will depend on personal preference and some on the parts/mods you've fitted. There are of course some rules which always apply.

Do you have coilovers with adjustable platforms, bounce/rebound settings and a choice of spring rates? Also do you have front camber plates?

Laser alignment is fine as long as the operator knows what they're doing. I tend to use the old fashioned methods such as " stringing " the car to adjust the tracking but I'm forever changing things and testing alternative settings so a trip to the laser alignment guy four or five times a month isn't practical also I take my alignment equipment to the track so it needs to be fairly compact.

Let me know what parts you have and how you prefer the car to handle such as understeer, oversteer, neutral etc. Also steering, do you prefer weighted steering with good self centering characteristics or light steering with good tracking abilitys? PM me if you prefer.