The butterfly effect, for cyclists

More fun with numbers! Just to see how much of an effect a very small change in equipment can have on my test rides up Old La Honda Road, I tried recalculating my power and such, factoring in tire rolling resistance for the two different sets of racing tires I currently use, using data from tire tests published here:

Why? Because I may have used different tires for my two tests up Old La Honda Road. No big deal, right? I mean, how much difference can tires make? My second climbing test up Old La Honda, which should have been faster, was actually about the same, and I keep wondering whether to care or not, and what could influence the results. Well... I can't remember when I actually switched tires, but this could illustrate how significant just one small change could be:

When I enter the climb data for Old La Honda Road in Tim Clark's new online climbing tool and assume that I used my Vittoria Open Corsa Evo CX tires (Crr of 0.0039), and weighed 154 lbs for the first test resulting in a time of 19:50 minutes, I get 301 Watts as my required power.

I know for a fact that I used my Continental Grand Prix 4000s on my second test (using data for the 3000s, which are similar; Crr of 0.0067) and weighed 151 lbs, and this gave me a time of 19:55 requiring 305W. That is 4W more required power than my first test, just from these tires, in spite of me losing 3 pounds of body weight! Wow! I guess I won't use the Continentals for racing any more!

It is interesting to see that my tire change alone could skew the results that much!!! Never mind headwind, temperature, breakfast and such. I wish I could confirm that I used the Vittorias for my first test, but I didn't make a note of it and now I can't remember. But it's likely that I did.

So, I could be getting more power through my new training, and I need to not worry. Not that I really was, I was merely curious, right? :-)