I recently fit a wider rear tire on a 2000 RK. Making sure the wheel is centered everything fits nice except minor belt to tire rub. I made a pulley spacer from 3/16 steel plate. It fits perfect and the bike rides great. The spacers you can purchase are aluminum. Is there any opinions why my steel spacer won't last long term?

 

Don't know about the spacer lasting long term. But your pulleys are very possibly not in alignment anymore. So the drive belt might have an uneven seating in them due to its width. The life of drive belts depends on the tension being distributed evenly across the full width of the belt. If the pulley and transmission sprocket are out of alignment the tension will tend to be concentrated toward their edges due to the belt being forced up against the pulley side wall. That's not good for the pulley the sprocket or the belt. Some people go to a slightly narrower belt to prevent this or shave some off the edge of the stock belt. Just something to pay attention to.

 

It doesn't make any difference what the material is that you used. On your particular bike it does come very close. The only time there is a rub issue is when you back up. The belt will roll to the inside edge of the pulley (tire side) only when you back up. It will run to the outside edge of the pulley when you go forward. Alignment of the pulleys is always a good thing but seldom do they ever run perfectly in alignment...even from the factory. I have 80k on a 2001 Road King using the bigger tire on it. It will scuff the white wall ever so slightly when I do back up but never bothers it going forward. I'm still using the original wide belt and pulleys. Hope that gives you some insight on it all

 

The pulley doesn't move,the spacer slides the wheel/tire away from the pulley,also the front pulley is wider than the rear so the belt will find its own path even if the rear one is moved slightly.Does not work on all bikes,I also had to go to the 1-1/8" belt and pulley to get enough tire/belt clearance.

 

That being the case there's no alignment issue.