I would think it HAS to be the rear because the speedometer moves on a dyno (if memory serves me) and it would do that unless the speed is measured from the rear.
2016 M2 | Long Beach Blue | 6MT... coming
2015 M4 | Austin Yellow | DCT... current
2014 Corvette Stingray | Z51 | Torch Red | 7MT - Sold
2012 MB C63 Coupe | Performance package | Obsidian Black - Sold
2011 E92 M3 | Jerez Black | Fox Red | DCT | Competition Package - Sold