SRAM Omnium crankset

The MTB kit has spacers because some MTB frames have 73mm BB shells. Cuts inventory in half if they make everything to fit the 73mm shell and then include 2 x 2.5mm spacers (cost <10c) to make it fit 68mm shells.

Isn't there something to do with bb mounted front mechs too, sure there's something that says spacers this way if normal mech, that way if bb mounted one.

I suppose the longer axle on the mtb ones pushes q factor up too but not really an issue on mtb whereas might be more of an issue on road bike.