Need wheel help!
 

I really know nothing about tire sizing other than the bolt pattern. I have some extra cash not going to motor parts right now, and I was thinking that maybe some fender flares and wide tires would be better than horsepower.

Step1: So anyways, I figure that the fender flares add 3 inches, and then a few more bills gets me some wheel adapters so I can run 5x4.5" bolt pattern.

Step2: I was lookin at this wheel

Question: What is rear spacing, and what would be a good size combo that won't stick out but get the max out of the flares. What size (not diameter, but width)?

And to a lesser extent, does anyone know a good combo tire for track and road racing or would it be best to buy 2 sets?

Sorry this is the wheel I tried to link to:
Cragar Wheels

Size: 15'' x 10''
Bolt Circle: 5 x 4.5''
Rear Spacing: 4''

Size: 15'' x 8''
Bolt Circle: 5 x 4.5''
Rear Spacing: 3.75''

Can someone please just help me out a lil on spacing and choosing the right size please? Just a guess if you think the 10" would fit under the flares? Or if I could even go wider?

Sorry to post whore, but want to make sure you know this is on an FB.