It appears OP's 5er has 7,000# rated axles, with a GVW of 16,000#, (I also saw 15,000#), but OP didn't follow up with additional information on his unit. IF 7,000# rated axles, will figure 5er has G rated tire capabilities..thus as one other poster recommended, I'd go with either Goodyear G614's or the Sailun S637 tires...don't believe at that weight one needs to purchase wheels AND tires to go to 17.5"...unless they have deep pockets. I believe either of the tires mentioned will be a more than capable tire with GVW's listed. My 5er has a GVWR of 16,975#, with 7,000# rated axles and GY G614's.