On 27 Jan, 17:53, Civet wrote:
I've used two coats of Hammerite Smooth on steel car wheels,

I'm not a fan of this stuff, but that's a real worst-case use of it.

Hammerite (and Smoothrite) is tough, but it's also stiff, brittle and
not especially adhesive. It likes to fail by flaking off, especially
if the surface beneath isn't perfect or you're flexing it. Wheels are
likely to be both.

I would suggest:

* Good cleaning / electrolytic / shotblast / degreasing / whatever

* Good primer. You won't go wrong with a nice heavy zinc-based primer
(Davids 182) but red oxides are admittedly cheaper. Number One isn't
bad.

* A surface coating that's tough against bending. Glyptal would be
great (costly) and anything black and bituminous is likely to be
excellent, so long as you don't mind black and non-glossy.

Your best bet is somewhere that sells truck stuff, not car stuff. I've
cans of Leyland Chassis Black that date from the last century and are
still the best stuff I've got for trailer refurb.