I need a little assistance guys.  I'm wrapping up my build on my x-cal and have a set of Shimano XT brakes to replace my old Avid Elixir1's.  The bike came with a 180 front / 160 rear setup for rotors.  I am wanting to go to a 160 front / 140 rear combo.  I already have what I need for the 140 rear swap, but am confused on what I need to do for the front...  I have searched the internet as well as MTBR looking for the solution but only seem to be able to find people going from a 160 UP to a 180.  Not the other way around.  Can anyone tell me what I need to do to change my 180mm front setup to a 160mm?

Thanks for the response.  In its current configuration there is a 20mm adapter between the fork and the caliper.  I was thinking I might be able to just straight mount it since I didn't see any options online for a smaller adapter.

When going from Avid Elixirs to Shimano XT I had to remove ALL of the spacers and adapters to get proper contact between the pads and the rotors.  Chances are, like mentioned above, you can probably just bolt the caliper directly to the fork mounts and be able to use a 160MM adapter.

If the mounts on the rear of the frame are for 140MM rotors then it'll be the same idea.

Decided to take the rear rotor (160mm) and put it on the front just for trail fitment.  You guys are right.  It mounted right up.  I bought a mount already to convert the rear to 140mm.  Just waiting on my rotors to come in now and it'll be done.  The hoses are going to be a touch long, so I "might" take them in to the local shop to let them shorten them up depending on how long they are.