sidewall bulge measurement ?

The nitto nt555r has a very narrow section width compared to tread width hitting the ground when paired against the BF Goodrich radial T/A the same size.
I was running T/A's, 295/50/15 that barely rubbed in certain circumstances. Swapped to nt555r's 275/50/15 having the same tread width and a 1" smaller section width. Gave me the same amount of tread surface on the ground and the extra clearance I needed.
I have a narrowed 8 3/4 and offset shackle kit.