Tire pressure did not affect power output over a non-flat 10.5 mile time trial course ridden in near identical fashion for three test pressures: 80/85 (front/rear) psi, 90/95 psi, and 100/105 psi .
Towards the end of the 2000s, bike-people started to embrace wider rims and tires running them at lower pressure. From 19 and 21 mm, 23 mm tires then 25 mm tires became the norm. Narrower tires for more speed had made intuitive sense but truths of reality don't care how you feel.
By that time, I had come across a range of religious tenets for tire pressure and tire/tube choices on road bikes. Many conflicting assertions: 120 psi all the time, go for as high a pressure as possible (over 140 psi), tubulars will always be faster, no, some clinchers are faster, use thinner tires obviously, no, wider tires are better. (And eventually crazytown-banana-pants fatbikes would appear with 4.6"/116 mm and 5–10 psi.)
The main benefits seemed to be that:
Still, wider tires less rolling resistance seemed unlikely. And the tires would be heavier. Cyclists like to fret over things and rotational weight is a solid fret-inducer.
I first used a Hed wheels with 23 mm rims in 2009. I had a Hed Jet 9 C2 on the front, and a Hed C2 Belgium rim with a Powertap and disc cover on the back (thanks to Wheelbuilder). A clear prescription to use lower pressure came with these wider, larger volume tires.
Now this one page of internal book of bike beliefs had been revealed to be without foundation. This was ... unsettling.
I realized that I had to reconsider the 120 psi I had been using for many years by that point, and doing so with no great conviction. I was simply copying what many other people did (who were also themselves copying; it's what we do).
Here's how I demonstrated to myself back in May of 2012 that lower pressure does not slow the bike down, and made handling and comfort better.
Very surprisingly to me at the time, there was no real variation in power.
Average power (W): 306, 306, and 309. The 309 makes some sense in that I was beginning to work inefficiently and I was using the wrong gears on some climbs. Well, more wrong than usual.
Normalized power (W) for each piece were indistinguishable. The Garmin 500 didn't record normalized power at the time so here are two measures calculated afterwards:
See the table below for more statistics.
|Pressure (front/back) (psi)||Distance (miles)||Time||Average Power (W)||Coggan Normalized Power (W)||Strava Normalized Power (W)||Average speed (mph)||Max speed (mph)|
|Pressure (front/back) (psi)||80/85||100/105||90/95|
|Average Power (W)||306||306||309|
|Max Power (W)||643||656||653|
|Coggan Normalized Power (W)||326||329||327|
|Strava Normalized Power (W)||313||314||314|
|Average speed (mph)||23.1||23.1||23.1|
|Max speed (mph)||47.4||47.4||42.8|
|Average heartrate (bpm)||139||151||152|
|Max heartrate (bpm)||158||167||169|
|Average cadence (rpm)||78||78||76|
Note 1 from training record: "I did not follow power at all on the second and third time trials as I used Garmin's course thing I stayed within a few seconds of my first ride, seeing up to a 16 second gap on the second effort. Dropped behind a little towards the end of the third and managed to just come in a few seconds ahead. The course thing worked impressively well."
Note 2 from training record: "The power numbers are solid power and I guess I trust them now. Still, I should be going faster with that kind of input, right?" Right. Various improvements helped in the next few years: Better seat, better tires, latex tubes, and, a big, big deal: leg shaving.
Note 3 from training record: "The chain slipped off the small cog on the third effort during the initial downhill and I managed to get it back on without stopping. I have to get that fixed."
General: Ride a lower pressure for both increased comfort and better handling, and less likelihood of flatting.
Personal: Using 80 to 85 psi, I've set all my PR times on the same bike in TTs and triathlons all the while getting older and generally more broken (existence is just the best).