You are going to loose 1/2 inch on all sides from the rim, plus the difference in tire sidewall. Plan on about 1 inch per tire. So the 4 above would be 3, the 6 between would be 4. Best upgrade on my TT years ago, I ended up going to 245/75/16 tires, and timed it to take the old tires off the TV and put them on the new rims for the trailer. Total cost was under $400 for the rims, the tire place mounted and balanced for free since I was buying more. I ended up with over 12k of tires on a 9900 TT. I put 22-25k a year on my TV (mostly empty - DD), so the tires have ~10k left on them when I change them, not enough for another winter, but more then enough for the trailer. The trailer ends up with newer tires when the current ones hit ~4 years old.