I then got a call from the garage owner saying I needed the tyre to be changed, and that the tracking was out and needed tow-in adjustment to prevent one-sided wear observed on that tyre, which I agreed to.
When I got the printout from the tracking machine I was astounded at the manufacturer's limits on the settings. The front wheel states tow limits of 0°00' to 0°10', and my wheel before adjustment was 0°23'.
After adjustment it read 0°05'. In other words they adjusted it by 18 minutes of arc, about a third of a degree.
I cannot believe that such a small adjustment will have noticable effect on tyre wear. It seems to me that manufacturers have such limits because they are easy to achieve, but users should be given much wider limits before adjustment is needed.
I've now researched this interesting subject, but can find no scientific treatment. The first 10 pages on Google are filled with garages offering tracking, laying it on thick about how important it is. The tracking machine's website has two videos of garage owners saying how quick and easy it is to check alignment and offer customers adjustment, and the added income paying for the machine many times over.
I was charged £145+VAT for it, and looking at my video again, there was no characteristic toe-in wear. I think I've been had! Any thoughts?