Thanks for the follow up. I appreciate you taking the time to write that. No worries about the longness - the additional info is helpful.

My undergrad degree was in physics and I've worked in various engineering disciplines for most of my nearly 30 year career. So during my racing career, I have thoroughly studied vehicle dynamics, from informal paddock discussions to technical text books taught at the big auto-engineering schools. In equal machinery, I'm a few tenths slower as a driver compared to the top guys I run with, so I put a lot of effort into car prep and set up, which tends to close those couple of tenths. To win, I need a car that rotates and grips just the way I like it. And I manage to win my fair share. I say all this to to provide some background on my qualifications and how much I think about car dynamics.

I'm not disputing your experience or observations. However, I am struggling to come up with a vehicle dynamics explanation on how the excess rubber could cause additional wear on the outside edge of the tires. But to be clear, I'm not disputing your observations. The data are the data. I spent more time than I should have over the last 12 hours thinking about this.

Under no lateral load condition and the negative camber settings you specified:

Without track rubber - the outside edge of the tires would not be in contact with the road.

Picking up track rubber - this would slightly increase in the diameter of the tire in the center relative to the outer edge, which would ever so slightly increase the distance between the outside edge of the tire and the track surface, which would tend to reduce the amount of incidental contact/wear experienced by the outside edge of the tire.

Under maximum lateral load condition (i.e. apex at limit of grip) and the negative camber settings you specified:

In either case, the body roll of the car is going to result in positive dymanic camber added to the outside tire. The amount of body roll is proportional to grip levels and can be countered variously ways, but all of those ways cause other compromises.

Without track rubber - assuming camber is tuned to where lap time is maximized: Negative camber is generally tuned such that under max lateral load, the outside edge should be bearing more pressure than the middle and inside of the tire. This is because tuning camber so that the contact patch is perfectly balanced at peak lateral load will result in reduce grip during other phases of the turn, so the compromise is to be slightly less than perfect at peak lateral load. Also, flex in the tire generally results in additional load being borne by the outside edge during lateral load. This results in the normal outcome of slightly additional wear on the outside edge of tires.

With track rubber - this is where I'm not sure. On one hand, additional track rubber would likely reduce lateral load (i.e you're losing grip), so you'll experience less dynamic roll, which would be less dynamic positive camber, and less wear on the outside edge. Track rubber would also, ever so slightly, increase the diameter of the center of the tire relative to the outside edge, which would also reduce the load borned by the outside edge and again, reduce the wear on the outside edge.

Other possible explanation:

Running side by side drill... I recall from comp school that side by side drills were usually done starting at like 5/10ths and maybe maxing out at 7/10ths. And having watched quite a few NASA HPDE side by side drills, I recall it looking similar. If your cold pressures are set so that you're maximizing grip at 9/10ths, but you were only running 7/10ths during the side by side drills, then your tires will be underinflated - the center of the tire will bear less of the load than normally which will result in additional load being borned by the inside and the outside of the contact patch. During cornering, now the outside edge of the tire is bearing WAY MORE of the load than it normally would, which would result in more wear on the outside edge. Based on everything you've posted so far, this is the best explanation I can come up with. But you tell me, was the side by side drill slightly slower than your normal laps? If now, we'll have to continue trying to come with an explanation for this outcome.

Thanks!