Join Date: Aug 2006
Location: Southern California
Bikes: Several bikes, Road, Mountain, Commute, etc.
The crank length is one variable, but if I read your post correctly, you also changed out his 39 x 53 for a compact 34 x 50. That being the case, Ross is (apparently) able to spin a longer crank arm at a faster cadence (RPM), both of which could be contributing to his new-found speed.
On my normal road bikes I use 172.5's whilst on my touring bike (Mercian Vincitore) I use 170's, as I do on my fixed gear bike. In both touring a fixed gear formats, I prefer the (easier to spin) 170's, whereas if I'm trying to max out my potential speed (slow as it may be . . .) I seem to go faster on the 172.5's. Your milage (or is kilometers?) may vary!
Rick / OCRR