I can't answer your question, but that strikes me as an insanely low speed for that power. How big are you?

I'd bet on wind. Most people aren't sensitive enough to feel a 5mph wind while on the bike.

Brakes rubbing?

More lap traffic last time? Did you swim better?

Wind conditions?

Same power meter? Calibration?

Same tires?

Same helmet?

Bike fit could have made you less aerodynamic if you overall "shape" isn;t as good. Meaning getting lower or longer could make you position your head different. Narrower arms might not be faster when factored in to your overall position.

Pacing? A 1.07 VI isn't a terribly smooth effort. You had the same at both races. But when specifically you applied more power vs. less power could change your bike split. Especially if there are wind and hills. 1.07 Means you had a lot of accelerations or coasting.

I can't answer your question, but that strikes me as an insanely low speed for that power. How big are you?

There are a multitude of things it could be, don't worry too much about it.

I did a sprint yesterday, and my bike performance was a huge disappointment. I did the exact same race and bike course in the fall. I expected to ride significantly faster this time, but instead I rode almost a minute slower. I rode with exactly the same power in both races. Though, that was not entirely intentional... I was aiming to ride higher yesterday, but did not focus heavily on watching the PM on my Garmin. These are the details and changes between both races:

• Distance: 13.8 miles, mildly rolling hills
• Temperature: 73° F (fall), 68° F (yesterday)
  
• Avg. Power: 252W (both races); 270W NP (both races)
• Avg. HR: 153 BPM (fall), 149 BPM (yesterday)
• Avg. Speed: 22.2 MPH (fall), 21.5 MPH (yesterday)
• Tire Pressure: 95 PSI (yesterday), I cannot remember for the fall race
  
• About 5 lbs. lighter since fall
• Fitter since fall
  
• Upgraded to Tririg cockpit from Bayonet 3 from the fall race
• Removed down tube bottle cage since fall
  

I cannot remember my tire pressure in the fall race. It could have been 100 PSI or 110 PSI. So, maybe higher pressure in the prior race was a factor.

I could blame the cockpit upgrade, but I did a 60 mile bike check ride about a month ago. I averaged 21.4 MPH, including at least a couple dozen (mostly brief) stops at intersections. I was wearing a regular bike kit with a non-aero helmet. That ride should have been the lower end of my speed that I would see this season. I held my position very well in the sprint, but somewhat poorly in the check ride. Unfortunately, both my PM and my HRM crapped out for that ride, so I have no effort metrics to look back on. But, it was not as intense an RPE as the sprint.

Based on the aero improvements, my current fitness, my check ride last month, I expected to ride around 23 MPH. 21.5 MPH was a massive disappointment and it cost me winning my age group-- I finished as the first loser in my AG (2nd place).

The first things I checked after the race when I saw my time was brake rub and tire pressure. Both were fine.

The only defect I can think of is that I noticed early during yesterday's ride that my handlebars were off-center by a few degrees. It happened in transport, and I decided not to stop and correct it during the ride, because I figured that the time to stop and correct it would be greater than the impact. Do you think that <5° handlebar angle offset could have cost me more than 1 MPH in speed?

Can you think of anything else that might have cost me significant speed loss? Could a 5° F lower temperature made that much of a difference?

What tires/tubes did you run in both races?
Edit: Oh, and what power meter?

What power meter are you using? Can you upload a screen shot of the power data charts from Trainingpeaks or whatever you use? I might be suspicious of those numbers. And if the numbers arent reliable, then everything else cant be compared. Why did the PM not work on your last training ride?

• You say you are fitter. Does your data from training show that? You rode the identical power with a 4 BPM lower HR. That suggests a slight fitness gain. What were you seeing in training? Im asking because it might point to your power data, or possibly your HR data not being reliable (you also mentioned your HRM didnt work on your last ride.)

• Have you checked everything else on your drive train to ensure it spins freely and isnt robbing power?
• If you could up load all the charts from Trainingpeaks for both rides. Im wondering if you lost time on certain sections of the ride for some reason. Climbing, descending, eating or drinking, out of or into transition?
• What bike are you riding? I dont know how much aero gain in terms of time on a sprint course youd get from moving from the bayonet to the tririg.
• Did you carry anything extra on your bike that may have added weight? More water, bigger tool kit, anything else new?

Im guessing either your PM isnt consistant or that it was in fact a windy day. For the wind, can you check how times in the results look year over year for others. Is there a trend that last year was faster than this year?