Biggest tire on Stock 67-69 Dart

Check the section width to tread width for a particular brand and tire. My car is a 69 Dart with SS springs (axle moved back 1.25" to center in wheel well) and the offset shackle. Had more room than I thought. The BF Goodrich G-Force Sport Comp-2 has a great tread width to section width ratio. I tried both the 275/40/17 and the 255/45/17. Both fit but the 275 would require I roll the inner quarter lip - plus The 255 has more sidewall and I like the look so I'm going with that.

Here's an example of the section width (actual width) to tread width (traction surface) of various tires and why I was impressed with the Sport Comp-2.

255/45/17 BFG Sport Comp-2 10" 9.7"
275/40/17 BFG Sport Comp-2 10.9" 10.8"

255/45/17 Sumitomo HTR Z II 10.3" 9.1"
275/40/17 Sumitomo HTR Z II 11.1" 9.9"

This is all from tirerack.com and I called and confirmed with a sales rep that these are as measured, but I'm not sure how or why they are so different. Hopefully it's real and I haven't been hoodwinked by marketing numbers. If true this seems really compelling to me. More tread and less sidewall width - exactly what A bodies need!