I agree with the review of the basic balance of the E92 as Birds BMW (BMW tuning specialist) have found - i.e. understeer -
"anti-roll stabilisers complement the chassis balance and trim. Fast drivers will immediately note the prevalent under-steer inherent in the standard BMW chassis. As a consequence we provide significantly more rear stiffness than the front, biasing away from understeer.."
http://www.birdsauto.com/sites/www.b...9210928311.pdf
..whilst I save my pennies for their "B3-3.5 Dynamics Package 1" I thought about how I might try to address the understeer balance without spending too much cash. Although spacers don't affect the stiffness of the springs or antirollbar, they do effectively lengthen the wishbone which achieves the same result. Moving the wheels further apart reduces roll.
My car is fitted with standard offset 18" wheels (225 fr / 255 r) I opted therefore to leave the front alone and add 15mm hub-centric spacers to the rear axle only. The theory being that doing this reduces roll on the rear axle, whilst maintaining the existing front balance.
Initial drive, and I can immediately feel a difference - slightly less roll at the back, less understeer into the bend and more steering 'feel' with better precision. On acceleration out of a bend, the rear feels better also - the only way I can describe it is as if I'd put much wider tyres on.
Cosmetically, the car also looks great, more squat. The tyres look almost flush with the arches now. For me, the front tyres look fine as they are without spacers. Besides, adding spacers to the front also, would arguably restore the original balance which is what I was trying to get away from.
For an investment of around £55 it has been well worth it. Cynics, as I did, will say why don't BMW just supply the standard alloys with an offset that achieves this without the need for spacers - i.e. I can't believe it would work. It does! I very much doubt that it achieves the same or anything near the change in balance new springs, shocks and antirollbar would achieve but it does get some-way there for a fraction of the cost.
Notes: only buy "hub-centric" spacers / ensure you have correct length (longer bolts) / clean the hub of rust dirt etc. and apply something like copper grease to surface before fitting the spacer, otherwise it will not come off again easily / torque the bolts to the OEM specs and recheck after first drive, and recheck a week later / most chain/franchised garages won't help you fit, so unless you have your own torque-wrench you'll need to find a local/independent garage, and even then some may not want to assist - whatever, you must use a torque-wrench to fit and check / spacers may affect insurance.