I have RH Alurad NAJ 200.

18" diameter by 8" wide all round, with a 45mm offset.
and the tyres were Yokohama AVS db V550 - Size 245/45R18 W 100/RF
The db standing for "decibel" as in quiet run tyres. I found that the van tramlined a lot on uneven surfaces and put this down to the width of the tyres on the front. I found that running them at 40psi helped this, but didn't cure it. They weren't that quiet.
On replacement at 20,000 miles, I went for some Continental Sportcontact 2 245/45R18 100w xl
and the difference is amazing! They are easily quieter by 50% than the yokohamas and the handling is impeccable. They no longer tramline and even put up with motorway ruts a lot better! So in my experience, 8" alloys are OK on the front but can be very sensitive to tyres.
245/45R18 is within 1% of the original tyre diameter.
Note: This does not constitute advice. Wheels and tyres are safety critical items. You are responsible to check information yourself.