Since I have a lot of free time on my hands, I decided to run some coast-down tests on the five high-performance recumbents I own to determine which is the fastest. The fastest should be the one with the lowest combination of air and rolling resistance. Hope the following report will be of interest to at least some of the members who are into high performance recumbents. I spent parts of the past two days making a total of 22 runs down the steep concrete path that parallels the spillway at WRL.
 
All the recumbents are equipped with high-performance, smooth-tread tires. I pressured the front tires to 110 psi and the rears to 115 psi. I crossed the starting point at approximately 15 mph and coasted until each recumbent reached its maximum speed. All of the runs were made under no-wind conditions at 100 degrees, plus. I made a minimum of three runs per recumbent and averaged the results. Average maximum speeds were as follows:
 
  a. 2010 Optima Baron – 26.8 mph
  b. 2011 Catbike Musashi – 26.7 mph
  c. 2009 Carbent Raven – 26.1 mph
  d. 2007 Catrike Speed w/26” rear wheel conversion kit – 25.8 mph
  e. 2009 RANS X-Stream – 25.2 mph
 
The above results can’t be used to judge relative cranking effort, because from my experience the Musashi requires less cranking effort than the Baron, and the X-Stream requires less cranking effort than the Speed at elevated speeds on the flats. My subjective opinion of cranking effort required to maintain a 21 mph cruising speed on the flats from least to maximum by recumbent is as follows:
 
  a. Musashi
  b. Baron
  c. Carbent
  d. X-Stream
  e. Speed    

Heat's really getting to you is'nt it.

Quote from johnnybent on Aug 1^st, 2011, 8:15pm:

 
You're just saying that because you're riding one of those slow X-Streams.    
 
 

Quote from johnnybent on Aug 1^st, 2011, 8:31pm:

 
You need to get with Kenny. He has the plans and material list.  

Coast down figures are fairly irrelevant, but a good power meter can eliminate all that guesswork!

Quote from aikigreg on Aug 1^st, 2011, 11:21pm:

Not entirely irrelevant, coastdown will give a comparison at the initial speed or for the same hill. While it won't give hard numbers it will still give relative strengths.

Quote from Bud_Bent on Aug 2^nd, 2011, 4:51pm:

 
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.  

Quote from aikigreg on Aug 1^st, 2011, 11:21pm:

 
Don't agree that coast-down test results are irrelevent, if the tests are properly conducted, but a power meter would definitely be a much better way to go. If I was Mark Cuban, I would have some Power Tap wheels built up for my bikes, and run some more tests.