Accelerated Tire Tread Wear, Help!

[tennforest]

Hello,
I'm the owner of a 1986 Virago 700 shaft driven. I purchased it two summers ago and love riding. Since purchasing, I've added all sort of goodies to the bike. Approximatley 1,500 miles ago, I put brand new Dunlop 404 tires on the bike. The front tire still looks brand new. My problem is the rear tire. It's already in worse shape than the tire I replaced. Tread depth for new Dunlop 404 is 9/32. The tread is slick in the middle 3 inches of the rear tire. My first reasoning for the accelerated tire wear was to much air. I've always kept 36 psi in the tire which is what is recommended. I checked allignment (by wrapping fishing line around rear tire and stretching past front) and it's only 1/8th of an inch off. I don't think 1/8th is enough to cause the tread to wear that fast and I'm not even sure how you would align the motorcycle due to being shaft and not chain/belt. The local yamaha dealership balanced the tires when they replaced with my old ones.
Thanks for reading and would appreciate and advice.
Also, I've used as many as three pressure guages at one time to make sure I was putting 36 psi in the rear tire and the arrow of direction is pointing in the right direction and I ride mostly solo. I've never burned out the tires. I've always been easy on the motorcycle and I'm the only driver.
Is 1,500 miles all that I can expect to get out of a new tire? If not, how many?

[Gummiente]

I doubt that it's an alignment problem, but you'll need to check it with a little more accuracy than the fishing line method; keep in mind that the rear tire is often wider than the front which will give a misleading indication. You'd be better off to tape two straight broomsticks to the rear wheel, one on each side, that extend up to the front axle - with the front wheel pointed straight ahead you then measure the distance between each pole and the front fork or other similar symmetric point of reference.

But because this is a shaft driven bike, you'd have other more obvious indicators if there was an alignment problem. Excessive freeplay between the shaft pinion and the ring gear, weird noises coming from the rear end (of the bike, not you ), oil leakage onto the rear hub, etc.

I'd be more inclined to suspect you had too much air pressure in the rear which caused the wear. Do you use the same gauge to check the tire pressure all the time? Try another one to see if the readings differ and don't go by the scale on the air hose at the local garage, they are notoriously inaccurate. Is the tire unidirectional? Check to see if there is an arrow molded onto the sidewall and make sure it is pointing in the direction of rotation - sometimes even an experienced mechanic will miss this one. Do you do a lot of two-up riding at extended highway speeds? This can accelerate rear tire wear. But at only 1,500km you still should have way more tread depth left than what you have now.

[poppygene]

I find this hard to believe! The 404 normally gives great tread life. Case in point: my sister-in-law's '87 Intruder 700 got like 12,000 (miles, not km's!) from the last set of 404s. 'Course, she's pretty easy on it, but still...

You been doin' burnouts? Use the front brake at all? Loan your bike to a "friend?"