I am an alignment tech in a small speciality shop. I drive Leafs, but have not personally experienced tire wear bad enough to bother doing any alignments on a Leaf yet. So my comments are general, but there is no reason why a Leaf would be any different than a Prius as far as tire wear analysis and remediation goes.
TIRE PRESSURES. Low pressure can exacerbate wear issues, but won't cause excess wear (assuming your TPMS light is not on...). In other words, the actual problem is elsewhere. But, I don't see any reason to avoid running tires at much higher pressures that the manufacturers recommend. You can safely put your tire pressures anywhere between:
Lowest acceptable tire pressure is on the door sticker, or in the owner manual- AKA the manufacturers recommendation.
Highest acceptable pressure is what the actual tire states, on the sidewall, as its max inflation pressure. Every tire has this on it. Most nowadays are 46 to 56 psi. No harm will come to your car if you run the tires at their max pressure.
Tire pressures at this high end give you much better energy economy, but a harsh ride. I prefer around 42 psi, as a good compromise. Only check your tire pressures cold, and consider direct sunlight the same as a hot tire. Never check them hot-it will just scare you!
BELIEVE IT OR NOT Most tire wear problems I see actually originate in the back of the car, in the rear suspension, or, even more often, behind the steering wheel. Ha, Ha. But true. The loose nut behind the steering wheel... So if your alignment is ok and your tires are losing their edges, look no further than your driving style. Especially if this is front tire edge wear.
ANALYZING PROBLEMS. If you rotate your tires too often, you will not be able to analyze the wear patterns and thus discern which corner of the car the problem is on, and whether is it a camber or toe issue. Camber is the tilt of the top of the wheel inboard or outboard and toe is the projected track of the wheel, and how far off from straight ahead it is. Five to fifteen thousand is a typical mileage at which tire wear becomes noticeable and diagnosable on the average car with issues. If you are seeing tire wear before this, it should be pretty easy to diagnose.
Very generally speaking, toe issues tend to cause feathering, and camber issues cause edge wear (and a type of edge wear called cupping). Lots of exceptions and blended wear happens, but this is a coarse rule of thumb. Feathering is discernible by sliding your hand around tire clockwise, then counterclockwise. Going one direction, the tread blocks will feel soft. Going the other direction the tread block edges feel sharp or raspy. Feathering comes from the feel of feathers on a bird. They could have used the fur comparison too. If you ever pet your cat or dog against the fur grain, well, you get the idea. But they called it feathering because it sounds cooler than furring!!
Edge wear means that the inside edge and/or the outside edge(s) are worn while the center of the tread is much less disturbed. Cupping is edge wear which is not even, but presents as flat spots or even scallops.
It is said that the rear suspension angles are not adjustable, but this is just 'towing the party line'. Most of my tire wear alignments are done on the supposedly nonadjustable rear suspensions (like a Prius or a Leaf). A really good alignment tech has access to either aftermarket shims or can fabricate shims to fine tune even a solid beam axle with a hub bolted to it, as the Leaf has.
THE NUMBERS, which I use on a typical front wheel drive/beam rear axle car are as follows. (Note the cambers are all negative numbers, meaning the top of the wheel is tipped in, closer to the center line of the car than the bottom.)
Front camber, between -.5 and -1.0 deg. Closer to -.5 if possible
Front toe zero
Rear camber also between -.5 and -1.0 deg -.75 seems to return the best handling/wear compromise.
Rear toe .3 to .4 inches (I shoot for .17 per side). Sorry, you can translate deg or mm if you don't like inches.
Front and rear, caster, toe, and camber should be within the manufacturers specs, unless you know what you are doing and have a good reason to deviate from that. None of these angles should vary from one side to the other by more than half on a degree. EG, -.4 on the right and -1.0 on the left is not acceptable, while -.4 and -.9 just barely does make it. Toe has to be equal left/right.
AND Camber out of these ranges as mentioned in a previous post will cause noticeable to extreme tire wear. Most alignment shops will try to solve tire wear in their front adjustments, and tell you the rear cannot be done. But you can tell by holding off rotating the tires and watching for wear in the back versus front. A problem in the front cannot cause wear in the rear and vv.
I hope this helps some of you.
