You will see a difference, but it's not because the Cd or Crr is different, it's because the Cs (coefficient of skin friction) isn't taken into accuont with coast down tests.
Instructables, how to measure the drag coefficient of your car:
Measure the drag coefficient of your car
help with simplified cDA/cRR formula
http://ecomodder.com/forum/showthrea...mula-3737.html