2X cranks and 3X cranks.. is there any difference?

ChILd_ReBoRn

What is the difference between 2x and 3x cranks? I see there are dedicated 2x chainrings to be bought, and I think that the only difference is the chainring spacing. Is this accomplished with the chainring shape, or is the crank different?

If I buy 2x chainrings and put them on my normal 3X deore crank, will I get a dedicated 2x drive or not?

Do I leave the BB spacers as they were ona 3x setup or not?

cooldad

The crank has the rings in different positions.

So no.

And no.

The Rookie

A triple has the middle ring on the nominal chainline, a double puts the nominal chainline between the two rings all for rather obvious reasons.

You can put double rings on a triple crank but the chainline isn't ideal.

Giraffoto

A triple has the extra mounting points for the third ring. If it's a square or spline taper fit, you can adjust the chainline by using different length BB axles - this is the solution that I used to run a triple crankset as a double. In my case, however, I was using large and middle chainrings and they were both on the 104mm BCD mounts. A 2x MTB set of chainrings is usually one 104mm and one 64mm BCD fitting and is the equivalent of middle and small chainrings on a triple, so you'll want to move the chainline out by about 2- 4mm. If you have a square or spline taper BB, try one with the axle about that much longer. If it's a Hollowtech threaded BB, move a 2.5 mm spacer from the non-drive to drive side. If it's press fit, I don't know if it's even possible.