I am replacing all 4 tires on my 763. I purchased the tires the other day planning on mounting them to the existing rims. Come to find out, 2 of the existing tires are foam filled. So I need to buy 2 new rims. Problem is, I can't find rims with the same offset (0.25"). New ones that I have found have offsets that vary from 4-3/8" (Ebay) to 0.38" (Bobcat). What gives? Does the offset need to match exactly on all 4 wheels?