Anybody running 18x7s with 4.5 backspacing front and 18x8 with 4.5 backspacing in the rear? I found a good deal and this is the only size.

Those sizes will work but they won't fill the wheel wells. To compare: 18x8 with 4.75 backspace in the front and 18x9.5 in the rear with 5.5 backspace. As you can see you are within the reccommended sizes.

Why wouldn't these sizes fill the wheel wells with the right size tire?

Why wouldn't these sizes fill the wheel wells with the right size tire?

Because you can fit wider and the same size tire on a wider wheel IS wider - .2" for every 1/2" of wheel I believe. Don't take it as a negative that's not how I meant it. The only point was to tell you that wider wheels will fit.

Thanks Jack, I didn't take it as negative, I just did not understand what you were saying. I value all forum information and advice.:thumbsup:

To compare: 18x8 with 4.75 backspace in the front and 18x9.5 in the rear with 5.5 backspace.

Jack is right on that setup above,that should work perfectly.
If the particular wheel you're looking at doesn't do 1/4" increments,a 4.5" b/s on an 8" wide front wheel will work too but 4.75" is better and 4.875" is even better.:thumbsup:
As you can see,you're pushing the wheel away from the outer fenders which is what you want.