As a companion to last week's post about White Industries R30, G30, and M30 cranksets (MR30), this week we wanted to take a look at the two chainring mounting standards that White Industries use on their square taper road, Eno, and 30mm spindle MR30 cranksets. This is an area that generates a lot of questions because both the VBC and TSR chainrings are available for both standards, but clearly aren't differentiated by name.
MR30 VBC outer ring (left) and square taper outer ring (right)
Both standards use a 12-spline interface, but the diameter of the hole, and therefore the size and shape of the splines is significantly different to accommodate different spindle sizes. A quick glance is enough to tell the two apart, and there is no possibility of installing the wrong one on the wrong crank: they're just too different. So is that the end of the story? Similar, but different and separate? Not quite.
While the two different interfaces are non-interchangeable, they do use some of the same VBC (Variable Bolt Circle) chainring system parts.
The VBC system uses two chainrings–one fixed to the crankarm, and the second mounted to the first–and both the small chainring and the VBC bolt kit are compatible with both MR30 and square taper-interface outer chainrings. This means that if you've been using VBC chainrings with your White Industries square taper road cranks, and you have extra inner chainrings, you'll be able to use those with your MR30 VBC outer rings. 
MR30 TSR chainring on top of a square taper TSR chainring
So to wrap up, here's a very brief summary of what is interchangeable (not based on crank interface), and what is specific to either the MR30, or the square taper system:
Crank SpecificNot
Not Crank-Specific
We hope this helps you get a better feel for how White Industries cranks work, but as always, feel free to contact us if you have any questions about this or anything else related to the parts we sell.
