Originally Posted by
Gnosis
I’m a physicist, as well as a perfectionist, so you may rest assured that my computer is setup correctly for its 29” diameter tires (which were inflated to 70 PSI for that high-speed descent). You simply failed to consider that there were additional mitigating factors as concerns the max speeds achieved by my Wahoo 29er versus my Trek 2.1 road bike. For the sake of brevity, I refrained from going into detail.
My Trek 2.1 road bike achieved its max speed of 44.0 MPH when the temperature was 48~50 degrees F whereas my Wahoo 29er achieved its max speed of 46.5 MPH when the temperature had risen to 67 degrees F hence, my Wahoo 29er had the advantage of the warmer less dense air to negotiate. I also didn't have to wear a bulky winter jacket per my Wahoo 29er's descent, further reducing air drag.
I wasn't referring to the max speed difference, but your statement regarding a 2-3 mile increase in average speed due to lesser rotating mass of tires (sorry, should have quoted). A 2-3 mph gain in
average speed over any substantial distance is not "slightly higher," but a huge gain in speed. Unless you are going from really heavy, fat knobby tires to really light, skinny road racing tires, you will not see a 2-3 mph gain in average speed. There are factors other than lesser rotating mass that account for efficiency gains, including lower rolling resistance and lower wind resistance. Keep in mind also that "29er" rims will not accomodate such a wide range, from heavy knobby to light racing tires.