[argonaut]

I must disagree wholeheartedly that "spacers" should not be used. So long as they are made from an appropriate material and are used with studs or bolts of the appropriate length to achieve the proper thread engagement then there is really no issue with a modest thickness spacer. The load path is still through the studs to the wheel, which sandwiches the spacer. So as long as toque and thread engagement are adequate, there should be no problems. Additionally for years different automotive companies have design cars that uses such "spacers" from the factory.

"Adapters" on the other hand can be even more dangerous, especially if not designed properly. In this design the load path is through the studs to the adapter, then through the adapter itself to the secondary studs, then to the wheel. So the critical failure point it the adapter itself. If I cracks or fails your wheel will decouple completely.

That said, I'm using 1.5" aluminum "adapters" (I still call these spacers, as they are spacing the wheels out, not adapting a different bolt pattern, but just semantics) on the rear of my blazer. I dont trust them completely but I inspect them regularly for cracks and fatigue. All-steel adapters would be a different story. You'll have to proceed at your own risk.

I certainly would not recommend that anyone use "spacers" without installing longer studs. In fact, even if you are using aluminum wheels you may need longer studs since the original studs are short, being designed for use with steel wheels.