Twitchy Steering on E36? Dodgy Offset?

[Crossposted again uk.rec.cars.misc,alt.autos.bmw if anyone disapproves let
me know!]

All,

The steering on my 1994 E36 Coupe has always seemed light. Sometimes a
little too light. Certain contours in the road (not always visibly obvious)
can momentarily pull the steering left or right. I'm beginning to suspect
this MAY be due to the aftermarket M3 replicas that were already on the car
when I bought it? (17x7.5 ET41)

Usually the steering is dead straight but sometimes an uneven surface it
easily cause the wheel to pulling a little too hard in one direction or the
other.

I suppose I could compare the offset/width of the steel spare (which I
assume is one of the original wheels) to the fitted wheels.

Besides the posibility of having incorrect offsets? Are there any other
factors that may make steering twitchy or is this par for the course? Is
there anything that could reduce this.

Lordy