Ideal offset for track days ??

[chief]

Good morning, I would like to ask whether the offset of a wheel greatly affects the behaviour of the car on a track?

I do a lot of track days with my car and last year I’ve been using OEM 18inch alloys from the M3 E46. The front are 8J (47 offset) that I used with 12mm spacers, so ET35 offset at the front and 9J (26 offset) for rear with no spacers. The car despite the weight of the particular wheels was very well behaved and predictable. This year I’ve decided to run with a square setup with 4 x 9J 18” OEM E46 M3 wheels.

With the square setup and no spacers installed, I felt (without driving it at a track day) like the car was “narrower” in the back when I took it for a drive around the city, compared to the front axle. Like the front was more settled and stable somehow. Even visually it did not look as good as the rear wheels were too tucked in compared to the front. I then installed the 12mm spacers in the back and ran the front without any spacers. So I now had a ET26 front offset and an ET14 offset in the rear.

I went on 2 track days with that setup and I was surprised to see that the car suffered from oversteer at even slow speeds on the apex and even during the turn, without a lot of revs. I’m now wondering whether that was caused by the spacers in the back or if it’s some other reason like the particular tires I used, track temperature etc.

Please note that I am using AST suspension with -3.5 degrees of camber at the front (toe out 0.25) and -2.5 at the rear (toe in 2mm). The particular track is very twisty and has 3 tight hairpins which oversteer is very noticeable, even without being on the gas. The tires were Kuhmo V70A medium compound, 265/35/18 all around.

I would like to hear what you think on this matter.

Thank you