Welding up bmx hubs

A coating can be applied to steel to facilitate its arc welding to aluminum. One method is to coat the steel with aluminum. This is sometimes achieved by dip coating (hot dip aluminizing), or brazing the aluminum to the surface of the steel. Once coated, the steel member can be arc welded to the aluminum member, if care is taken to prevent the arc from impinging on the steel. A technique must be used during welding to direct the arc onto the aluminum member and allow the molten aluminum from the weld pool to flow onto the aluminum coated steel. Another method of joining aluminum to steel involves coating the steel surface with silver solder. The joint is then welded using aluminum filler alloy, taking care not to burn through the barrier layer of silver solder. Neither of these coating type joint methods are typically depended upon for full mechanical strength and are usually used for sealing purposes only.
and no the spaceing of a bmx frame and a fgfs bike are the same :o

That would be welding or brazing of aluminium to aluminium or some other nonferrous stuff, which happens to be surrounding the steel. Off the top of my head, the only way to actually weld steel and aluminium would be friction stir welding; not useful.

Oh dear, I'm rising to this stuff. I think it might be time to go for a ride or something.