When I did the brakes recently, I noticed that the inner shoulders were both noticeably worn - one of them showing canvass (although there was some evidence that this side may have been rubbing on a dropped arch liner). New tyres were ordered and fitted. After driving to work (about 60 miles) I felt the temps. The front tyres were both warmer on the inside.
The obvious culprit is toe, but I've just checked it, and I'm actually toeing in by 15 minutes. Toe in would give outer wear, right?
The other possibilities are:
Camber: but it's double wishbone, so dropping the height doesn't have the same amount of effect as it would on a McPherson strut. I've run much greater camber on the S14, and never had this kind of wear.
Track: It runs a little extra track owing to the spacers fitted at the front, but I can't see how that would make a difference.
Finally, it's worth noting that there's been no significant set up change since I changed the steering rack, which was almost 2 years ago to the day. At that point I had the tracking done, and it felt a bit dead, so I toed it out a touch. This also induced bump steer, so I dialed it back again. Everything else has been the same in for that period: ride height, track. The tyres had been on about a year. The previous set wore evenly.