We present a new set of photometric transformations for red stars observed with the Sloan Digital Sky Survey (SDSS) 0.5 m Photometric Telescope (PT) and the SDSS 2.5 m telescope at the Apache Point Observatory in New Mexico. Nightly PT observations of US Naval Observatory standards are used to determine extinction corrections and calibration terms for SDSS 2.5 m photometry. Systematic differences between the PT and native SDSS 2.5 m ugriz photometry require conversions between the two systems which have previously been undefined for the reddest stars. By matching ~43,000 stars observed with both the PT and SDSS 2.5 m, we extend the present relations to include low-mass stars with colors 0.6 ≤ r - i ≤ 1.7. These corrections will allow us to place photometry of bright, low-mass trigonometric parallax stars previously observed with the PT on the 2.5 m system. We present new transformation equations and discuss applications of these data to future low-mass star studies using the SDSS.