225/70R15 on a 15x5.5

will that wheel work or is it too skinny?

Look it up on the net but personally I think you are pushing it. I had 205/70's on 5.5 Volare wheels and that was a stretch.

Goodyear and Firestone both say 6" - seems narrow to me.

I have 225-70-14s on a 14X5.5" and the are ok.

They'll fit

I used to run 225 60 14 on a 5.5.

It was a 69 dart with a 340.
I'll add that the car had 1 1/8" sway bar added to the front, and 3/4" bar on the rear.
It was the best handling mopar I'd ever driven, both before then, and since then.

Careful with "they'll fit" --fitting and performing are two very different things. A skinny wheel (relative to tire) will have a LOT of roll when side forces are applied.

Yes they will 'fit' but the tire is not likely to perfrom anywhere near its optimum when mounted in this manner. Just my two cents!

I run 22570R15 on factory 7" wheels.They fill out better compared to narrower rims.
Minimum width for 22570R15 is 6" and maximum permitted is 7-1/2 and 8"

I work at a Goodyear tire garage.
From my "book"