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

[manos///3]

Play with suspension and tyres air temp settings.


Stiffen front or loosen rear bumb/rebound to reduce oversteer.

[shimmy]

As per the original question, I don't think the offset ie track width has as much affect as you are experiencing. It is much more likely if no other geo changes have been made that tyre pressure, temps are more likely to be the cause of you changing grip levels.

The initial wider rubber at the front will have increased front grip all eske being equal which will make ou feel like less grip at the back as the rear will be more likely to be the first loss of grip you notice as the front tucks in.

I would check temps and pressures carefully and make sure the geo is good for that track and conditions.

[billyboysm3]

I run this setup with those rims, fitted fresh cups on last night and took it for a blat and well chuffed, handled as I thought. Im running no spacers. Going to Snett on Sunday so will see how they compare to the might DZ's.

[DuncanR]

Personally i knocked my camber back from -3.5 to -3.0 and felt it was a lot better for it, in particular tyre edge wear.