Originally Posted by
fietsbob
Crowned Road, you are on a slight slope..
...
+1
Left side off center wear is perfectly normal in the USA because roads are crowned, so you're generally riding across a slight slope.
The wear will be biased to the right if you live and ride in the UK, Australia or other "drive left" countries.
BTW- if you don't see a slightly left side wear bias, there's something wrong, because this would mean that the bike was perpendicular to the angled road surface, and something is causing it to be off plumb.