Though my wire wheels are silver/grey and not black, I am personally not keen on Hammerite.
I am fortunate to have a model shop close by and have always found that Humbrol enamel to do the job well.
For me, easier to use and there is a wide range of each shade of silver/grey.
Bud
4/4 - Stanley
Yes I've thought of modeller's enamel paint like Humbrol, glad to hear it worked.