I seriously doubt that the left hand turns being longer than right hand turns cause that much extra wear. The reason is that, as a highway engineer, I have access to alot of mapping software. So when I first heard this theory, I measured a bunch of turns on several of the projects we are working on. The difference in length of the turns, when measured along the center of the lanes is less than 6% (usually closer to 3% to 4%) in all but the very sharpest of turns (like intersections, etc.). And in those cases, the speeds should be low enough that you wouldn't be causing too much wear on the tires anyways. I get about 10,000 miles out of a set of tires. Lets assume that half of those miles are straight (or nearly straight) and the other half curves. I also think that, unless you ride in alot of circles, it is a safe assumption that those miles would be equally split between left and right curves. So that means about 2500miles in left turns and 2500 miles in right curves. So assuming a high average of 5% longer for left curves, that means that you have perhaps travelled about 125 miles farther leaned over to the left than you have leaned over to the right. Are you going to tell me that you can see any real appreciable wear in just 125 miles?? Lets assume I way off, and that number is doubled or tripled...we are still talking about less than 500 miles difference. I don't buy that theory.
I voted other because I think there are lots of reasons the left side of the tire, for most people, wears faster than the right. I think the crown has alot to do with it. But mainly, I think it comes down to people riding more aggressively through left turns because usually the sight distance is better through the turn because you can see across/through the opposite lane. On right turns, you are looking through the area off of the road. Sometimes this is obscured by weeds, guiderails, hillsides, trees, etc. And I also think that alot of people, for whatever reason, are just more comfortable with left turns than right turns. This could be due to the placement of the controls of the bike. The throttle and both brakes are on the right. And it might just be that leaned over into a right turn with these controls on the low side closer to the ground causes some discomfort for some folks. A few years ago, I concentrated on riding through right turns more aggressively, and I actually found that I evened my tire wear out alot. Now I am only getting about 7000-8000 miles from a set of tires...worn out all the way across.
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