Cush Drive (Rubber Dampener inside Wheel / Rim which transmits sprocket power to the wheel.) is not needed on our bikes because of the belt drive on an all original XBs. This is because the belt actually stretches and acts like the rubber dampener. Once you modify the bike, and install a chain drive, you lose that feature of the belt. That is probably part of the reason why the bolts have loosened up and broken. The other is the spacer, definitely a lot of torque transmitted between the wheel and the sprocket. The spacer will act as a fulcrum with the bolt (wobbling it in the wheel) and cause the threads to expand in the aluminum. I don't know if a harder grade bolt will solve this issue with a big tire, no cush drive, and lots of torque. If you're easy on the throttle, you may lessen the chances of having this happen again.
I have taken sheared bolts out of an aluminum wheel before with the bolts being lock-tighted. (Red or Blue) This part you may not like to hear... Given the small size of the bolts, when using a bolt extractor, I had to use an oxy-acetylene torch and heat the bolt hole and surrounding surface. This will break the bond of the lock-tight, and expand the aluminum around the bolt. Allowing you to use a small bolt extractor. If you don't heat it up (been there) the extractor will snap. Now you have a harden piece of tooling lodged in the wheel, which will be a real headache drilling through. Also, if the bolt is stainless, when drilling for the bolt extractor, use a new drill bit, slow drill speed, and lots of drill specific oil / tapping fluid. Otherwise you will burn up the drill. When finished, you would have to paint or get the wheel powder coated.
