i'm 6'2" and 260lbs. and riding- 42/13 (85 inches), never have any problems with breaking or slipping.

there are two powergrip models... one has a friction clamp and the other actually thru-bolts the strap. i'm using the clamps and still no problems.

shants is right about the pedal strike. even with 165's. i scrap all the time.