Re: 12 Slotters
I'm guessing you mean 14X6" rim?
The best you'll get safely is a 225. A 235 might fit but it'll be very sucked in and potentially dangerous.
12 slotters can be widened quite cheaply. Speak to your local mag joint. Cost me $75 for two to be widened to 14X7" a couple of years back. I've since found the place overcharges a bit, but who knows, they might have done me a good deal that time.
A 14X7" rim will take a 245, *possibly* a 255 and 14X8" will handle up to a 275.
Just like a Tsunami.