Pitbull said:
Your 265/70's would be a little taller than the OEM 265/65's but the tread would be narrower. It's based on the aspect ratio.
Correct me if I'm wrong, but I believe the width in either of the two is the same -- 265 millimeters (10.4 inches). That's what the 265 means.
The 70's are taller, having a taller sidewall, because yes, the aspect ratio is different. The 70's have a sidewall of 265 mm x .70 or 186 mm (7.3 inches), whereas the 65's have a sidewall height of 265 mm x .65 or 172 mm (6.8 inches). So yes, the 70's are have an inch greater diameter and sit 1/2 inch higher.
However, unless I'm missing something, they aren't narrower. Both are 265 mm wide.
Now as far as the original question -- contact patch; the width is only 1 of the 2 dimensions. I won't pretend to fully understand the determination of contact patch size, but I think it has to do with width, sidewall stiffness, diameter, air pressure, vehicle load, etc. I might be wrong, but my guess is the 70's actually have a larger contact patch. They will, however, probably have less sidewall stiffness (at least in a given line of tires) and this probably effects cornering more than contact patch.
Anyways -- my 2 cents.