How fast is your bike, really?

    I've wondered about that since I don't use a computer on any of my bikes.  People talk about it all the time at group, club and charity rides.  So I assume it's important.  A more important question to me is how much difference do I experience from one bike to another under normal riding conditions.
I decided to take the same route, at the same time of day in the same weather conditions and just ride however I am comfortable on each bike.  I wasn't going to do an all out time trial pace or attempt to get everything out of the bike, just ride at my normal cadence to see if size, weight and tire size made a substantial difference under normal riding conditions.  It makes sense that given a constant cadence, one would be faster on a lighter bike with smaller firmer tires because you would ride in a higher gear .  But how much faster?    Using Map My Ride out of sight in my pocket I rode a length of MUP which is paved and set on a North to South route.  Making the route and returning, the effect of the prevailing west wind would be negligible.  Riding the 7 mile route:

 my '87 Trek, a 21 pound road bike with
 25 mm Panaracer tires inflated to120PSI,

 clocked a blistering 14.9 MPH.

 Sam Hillborne, a 24.5 pound bike with
 32mm Panaracer tires
inflated to 95PSI, carried me at 14.5 MPH.

 The Hunqapillar, a 30+ pound 29er touring bike
with 50mm Schwalbe Big Ben tires inflated to 75 PSI,
 lumbered in comfortably at 14.2 MPH.

Byron, my Soma mixte, a 27 pound city bike
 with 35 mm 650B Schwalbe Kojak tires
inflated to 95 PSI, took me around at 13.5MPH.

     Now what does all this mean?  It's a totally intuitive, empirical study confirming that I ride pretty consistently on most equipment.  It was a short distance, I didn't monitor my heart rate or anything, but the results were pretty predictable.  Two things were a bit surprising.  The difference between the fastest 3 was so narrow.  That may widen or narrow more over longer distances, I don't know, but I was expecting something like a mile per hour difference between each of them.  It's also a blow to common bike wisdom that the slowest bike was not the heaviest, nor did it have the biggest, softest tires.  What might be at play there is the other equipment.  Byron, the Buena Vista, has a dyno hub in front, which creates more resistance, and a Nuvinci drivetrain which is hydraulic and has a completely top secret and unknown efficiency rating.   

      In the great scheme of things it will make for interesting reactions from spandex hamsters determined that over equipping is everything.