The only thing they can adjust is the toe-in(out) and if that was wrong it would affect both sides the same. I can't visualise any alignment problem that would cause even wear right across the tyre - I assume it is even around the tyre as well? The only possibility I can see (apart from a defective tyre or one that is more worn than the other) is a dragging brake or wheel bearing - and I would have thought that would show other effects (pulling) before it showed tyre wear.
If the wear is NOT even round the tyre but is in one place, it is a bent or out of balance or loose wheel (or with dirt behind it), or a bent or damaged brake disc, or possibly a damaged wheel bearing. (or, again, but very unlikely, a faulty tyre)
John
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
Bookmarks