2.2" MT rims didn't fit for me on the Caldera: the bottom of the A-arms where the hubs mount is too wide to fit in the rim. If you want MT rims look for anything 2.8" fits on the Stampede 4x4 (or front of the 2x4). If you have the Caldera SC then Slash or Blitz rims work (SCTE/Tekno/SC10-4wd rims would be too narrow). If you have the buggy... then I have no idea as I've never tried those rims
This was my Caldera with stock Traxxas Stampede 4wd 2.8" rims and Proline Badlands tires: the width was perfect. Stampede 2wd rear rims are narrower and worked OK on the rear of the Caldera... but rubbed on the front (which has a wider A-arm/hub).