I have a 2015 F56, and every time I look at the car from the rear, it looks like the rear tires are in a shape like this -- /[rear]\

I looked it up and it's called negative camber, which is probably not adjustable.
http://www.autocraze.com.au/wheel-alignment-guide/

Will this have any effect on premature wear on the corners of my tires?
I'm not an aggressive drive and mostly drive slow and steady. I currently have about 4000 miles on mine but don't notice any difference in wear. In a straight highway if I let go of the handle, after a few seconds I see the car heading a tiny bit to the right so I have to push it left a little. But this could be related to tire air pressure. I have 39.4(FL) 39.5(FR), 37.5(RL) 38.5(RR) right now.


Another question, do you guys do tire rotation? I read some people just skip tire rotation. I did it once on my Mazda CX-5 when it had 7000 miles, and those 19" wheels were really heavy.

 

If you don't rotate the tires (about every 3K - 6K miles is a good interval), the
rear tires will wear out on the inside of the tread faster than the middle or outer
tread, but the rears wear out about half as fast as the fronts in general.


MINIs usually have about -1.5 degrees of (negative) camber +/- 0.5 degrees.
If lowering springs or coilovers are added, there is more negative camber than
that and you can get more pronounced premature wear of the inner quarter of the
tread. There is a small amount of camber adjustment possible on the newer MINIs,
(after about 2004-2005 as I recall), and further adjustment is possible if you replace
the stock fixed rear control arms to aftermarket adjustable ones. Just make sure you
re-set the toe-in (0 to a small amount of toe-in) after adjusting camber.

 

Rear camber is adjustable on the MINI, has been since MY2005.

Camber has to be matched to the tire, suspension kinematics, and driving style. If your car is factory-stock, hasn't been wrecked, then the camber is likely fine, as is the tire wear.

As for your alignment, it's probably fine, but possibly not perfect as it sounds like there's a bit of thrust, or it's just tramlining. Car alignments from the factory are often much more precise than the roads you're driving on. If you have a genuine concern, have your dealership check the alignment.

Tire rotation, up to you. If you want to replace the front tires 2x as often as the rears, then no. If you want the whole set to wear even, then frequently rotate. Every tire model reacts differently to rotation, some get louder temporarily, some get quieter. As usual, "It depends".

 

It takes a whole lot of camber before you'll notice significant premature tire wear, in my experience.

 

Recently had the dealer perform the 12,000 mile service when the indicator showed up on the info screen. Asked dealer to rotate tires too... he said they would measure the tread wear and if there was a measurable difference between F/R, they would. Well, there was note quite the amount of wear to trip an automatic rotation but I had them do it anyway. Past experience with other cars (dozens!) proves that you can get quite a bit of more mileage out of the set by rotating and keeping the air pressure properly balanced. Of course staggered fitment is an exception. Handling seems to be measurably affected when there is varying pressure particularly on diagonal corners of the car. I always check and/or fill the tires in the AM when the car has been in the garage overnight and out of the sun/weather to get the truest cold tire pressure read.

 

I always rotate between 5 and 6 thousand miles.I like to replace tires in sets of four.Slight right drift (not pull) may be due to crown of the road.