I normally go off the outdrives. When the outdrives are wore, I sell it. But it takes a while for me to wear them out. maybe a year plus in 13.5/17.5. Then sell and buy a new car. lets say you can sell yours for $150 and buy new for $279. So for $129 you get a fresh car. How much would a chassis, diff and a few misc parts cost. Keep your alum tlr upgrades if they are in good shape for the new car.