OK, final verdict: Yes, call me perfeccionist. But, if I get this wrong I might be thinking I'm going faster (or slower) than I really am! Anyway, here it is: It's a big difference when you measure the roll out (circumference) with the bike alone, versus with the bike weighed down (with your own weight). When I did the measurement with the bike alone I got the 2105mm I mentioned before. With my weight on the bike, and the tires pumped to the correct pressure, I get 2090mm. So, pretty much, I'm sticking with Cateye's measurement of 2096mm. Again proves that the meaurement on the SIGMA manual is all screwed up. Now, when I look at my speed and I see 30MPH, I'll be happy to know that I did everything I could to make sure that's correct!