I guess i'm lucky. I have not had a wheel alignment in the last 3 cars. I did have the '94 Corolla (at 125,000 miles) aligned after I replaced the front half-shafts due to worn center cv joints.

For simplicity, I figure a 3000 lb car would have 1000 lbs on each front tire. The rears about 500 each. I'm guessing, could be more weight is up front. I saw somewhere about the front and rear weight ratios on cars, but now I don't remember where.

My tires always wear flat on the bottom probably due to my easy driving. If I did have to make a quick turn, theres lots of edge rubber there to do it with. With the front tires doing the majority of the stopping. I like to have lots of tread up front for braking and keeping the car from skiing in a heavy rain. These are some of my reasons I like to rotate.