Some more data. This is an HS 420 run as a rear tyre only for between 1200-1400 miles.

It's 23-622 or 700x23c. Clearly marked on the side of the tyre. Schwable allows a deviation of ± 1 mm new. The rim width is correct.

The treadwear is absymal. I'm 188cm/80kg (6'2", 176#) and if I recall, you're at 215#, so your treadwear might be even worse.

The glass/debris protection is good. I have 4-5 gashes like the two in the photo that go down to the green gaurd.

They're cheap, about £18 or so each.

I'll stick a caliper on it tomorrow, measure 3 spots and provide a mean/std dev/std err for you.