So, I noticed this cracking (?) On my tire this morning. It goes all the way around. I added air yesterday because I noticed my guage read 20 psi. I aired it up to the recommended 36 for riding double with my wife and didn't notice anything amiss at the time. Road for an hour or so. We combine to to total of 330 lbs. The wife says she smelled burning rubber while we were riding, but I didn't notice anything.

No unusual surfaces, a fair number of speed bumps, some train tracks, top speed around 45 mph. Any thoughts on cause? Would it be idiotic to ride in this condition? Tires are Metzler 880s. Tread wear doesn't look too bad. Exact age and mileage would be a question for Lancer. I've put on 400 miles or so since I bought it from him. Any thoughts would be appreciated!

That looks like it might be the head of one of the bolts that go through the rear fender from the inside, that hold the chrome side pieces on. Do you have saddlebag supports on your bike, or a 140/90 instead of the OEM 140/80 rear tire?

That is definitely caused by the rear fender bolts rubbing the tire.

What size rear tire is it?

It's a 140/80.

I'd recommend replacing the hex head bolts with something that has a smaller head. Button head bolts that have an allen socket in the head or something similar. On my bike I also had to move the mounting tabs for the saddlebag supports to the outside of the fender, between the fender and the chrome decorations, in order to have enough clearance. Even after changing the bolts the edge of one of the saddlebag support mounting tabs  on one side was still lightly hitting the tire going over big bumps. I weigh about 170 with all my gear on and don't carry a passenger. However the roads that I typically ride on around here are awful.  I'm running a 140/90 Shinko 712 tire and the bike still has the OEM shocks.With a 140/80 tire you might not have to move the supports.

It's hard to see how deep that grove is in the tire from the pic. but the tread groves are always deepest on the sides ,(the center of the tire wears faster) I'd think about replacement just for safety. I'd also check to make sure the spacers that fit on the shaft just inside the swingarm are install correctly ,they are two different lengths, the longer one goes on the drive pulley side, if reversed the wheel would be pushed closer to bolts that did the damage.

I have to agree with Antmanbee ,Get a new tire. There's two things you NEED on your bike,  good tires and good brakes .If you don't have them you could be seriously hurt ! If the bike doesn't start or run it can't kill you. If the tire fails at speed your in big trouble!

What does the date code on the tire say?  It will be a 4 digit number that is burned/etched in the rubber - it will look a bit different than all the other letters and numbers on the tire.

The first 2 digits are the week, and the last two are the year......2714 would be the 27th week in 2014.  About 5 years is the limit for me to feel safe as the rubber begins to get pretty hard and traction is compromised.

The "new" groove isn't any deeper than the tread - so that alone wouldn't cause me to replace it.