2007 Nissan Maxima

What are you measuring? Ride height is not that critical for good tire wear. If it was, just remove one of the dead bodies from the trunk. :) Actually, the rear will sag when there are passengers in the rear and that won't cause tire wear in itself. The place to start is with a four-wheel alignment. The rear camber and toe readings will tell what is causing the tire wear.

Can you describe the wear pattern? If one tire is worn excessively on just the inner or outer edge and it is smooth, that is camber wear and will affect just that tire although the same problem could cause the other one to wear that way too. If there is a sharp edge to each block of rubber on the tread that you feel when you rub your hand across it one and not the other, that is toe wear and will always affect both tires even when just one is misadjusted. Sometimes both tires don't show exactly the same wear on the rear because there is much less weight on them than on the front.

I'm sorry I don't know which type of suspension is used on the rear of your car. I find it hard to believe that a three-year-old car has sagged springs already. If you have independent rear suspension, incorrect ride height can affect tire wear but it would have to be a good inch or two low to be a potential factor. One rear seat passenger will cause that. If you have a solid rear axle, (you'll see a tube, square channel, or complete cross member going from side to side, supported by the springs), ride height will not be a factor at all. On those systems the wheels are held solely by the axle and it has no idea how high the body is sitting on the springs.

You might consider visiting a tire and alignment specialty shop. The aftermarket industry is always coming up with alignment fixes that are not approved by the car manufacturers. That doesn't mean they aren't safe and effective. It mostly means the manufacturer doesn't want to pay for those modifications under warranty. They insist their dealers use factory-supplied parts because those cost them much less money. Once the car is out of warranty, the mechanic is free to use whatever means is necessary to solve the problem. This is a really huge deal with Fords that come from the factory with all kinds of tire wear and alignment problems that customers don't know about until after they bought the vehicle. There are entire catalogs devoted to aftermarket "problem solver" parts. The biggest percentage of those parts are for Ford products but there are similar parts for every brand of car and truck. Tire shops are very concerned with proper tire wear because they don't want to have to warranty their tires due to misalignment issues. These guys also attend a lot of training classes that cover these problems. As a former Chrysler alignment specialist, the factory training classes covered the factory-approved fixes. Some of the trainers mentioned some aftermarket products briefly in passing, but they pointed out those were to be only used on out-of-warranty vehicles. If the factory fixes didn't solve the problem, there was something bent or some other problem existed. Since I also worked on a lot of trade-in cars I attended a lot of those aftermarket classes put on by Carquest, NAPA, and Moog. I learned a lot of things to look for that I didn't get from the factory schools. You should also keep in mind there are some tire wear problems that just can't be solved. Every alignment technician knows all too well about Ford's problems so all we can do is educate customers on how to reduce that wear as much as possible. The is no similar history for the Maxima, otherwise you would see similar tire wear on all of them. Unless something is bent there is going to be a way to fix the tire wear. If the rear tires aren't worn out yet, the mechanic might suggest rotating them to the front after the alignment is taken car of. With the higher engine weight on the front, the uneven wear will start to go away on those tires. If they are left on the rear, a choppy wear pattern will cause the tires to hop a little, (you won't feel it in the car), and the wear will continue. If the wear is just on one edge of the tire and it is smooth, that will straighten out once the alignment is set correctly.