Quote from Bud_Bent on Aug 2nd, 2011, 4:51pm:Coast down is too affected by gravity. If you load the bikes enough to make them weigh the same, you get a better test.
I've seen a similar statement (weight as a variable) made in some coast-down testing literature, but no explanation was given. Weight affects rolling resistance, so maybe that was the reason for the statement. Bob M. reminded me the other day that we learned in our physics courses that in a vacuum all free falling objects accelerate at the same rate, independent of mass. Aerodynamics accounts for the difference in terminal velocities of two free falling objects in the atmosphere, not their weights. This (along with other minor variables, such as rolling resistance) sounded reasonable to me to explain the differences in various recumbents' terminal velocities attained during roll-down tests on inclines.
I think the variables that introduced the biggest errors in my test results were the varying running start speeds (I was shooting for 15 mph), computer inaccuracies, and the winding concrete path. According to literature, I should have selected a 1/4 mile long straight slope of at least 5%, and should have utilized standing starts.