I'm not going to pull the trigger on this set of wheels until I know I have a tire that will fit. Theoretically wheel is 18x15".

I love BF goodrich and they make a 345/30-18, but the section width is only 13.8. There's also the M&H Racemaster in 345/35-18. Both of those tires are under 27" OD (which is imperative to my build) Will either of those tires safely stretch on a 15" wide wheel? If I went with a 14.5" would that work?

There's the Mickey Thompson sportsman S/R Radial 29'' x 18''R - 18LT which is meant for a 15-16" wide rim. But the whole point of the car is to be LOW LOW LOW and the amount of work that would be needed to get the car to not have a raked look and lay frame would be ridiculous. Plus they don't really offer a tire that'll fit the 18x12's up front. The S/R's look great and are affordable so i'm not against using them but I just don't know what to do.

The car doesn't necessarily NEED uberwide tires in the rear... but we also haven't dyno'd it yet. So it may. Can anyone PLEASE help me out??

 

You would be better off with a stickier tire if you need traction rather than just a wider tire... and Hoosier and Kumho make some real sticky tires in 345/35-18...

If you really want something wider and close to 27", switch to 20's, and Pirelli makes a 345/25-20 that is 26.8" diameter... or, you could do a 345/35-19 - 28.5"

 

But the question is will 345's FIT on a 15" wide wheel

 

All the manufacturers say between 12 and 14" roughly... Although not ideal, I'd probably still do it... is there a specific reason you want a 15" wide wheel?

 

I'd run 16" in the rear if I could but they don't offer the wheels I want in them. I can run 15" wide in the lowest offset possible and only need 2 inch flares. I really don't think a section width of 13.4 will fit on a 15 inch wide wheel safely.