Thanks for the responses! This really is hypothetical, so far... I'm running just barely below max tire and rear end with my rig. Have to be careful not to put too much stuff in the Fifth or truck on a trip. Currently shopping for a heavy bike rack to put on the fifth's trailer hitch, to help take a few pounds of tongue weight off! So it is informational at this point - tires are obviously the very critical part, but I was wondering "what else?" happens as you exceed the limits...and you all have helped educate me on that.