Originally Posted by nickw
I believe it has to do with the fact that the rear is just accelerating you, who cares about tire width on the back. You can save the weight by running a smaller tire with no drawbacks. I personally like the way a small tire feels on the rear, feels more 'precise' but I ride the mtb like its a 20" so it might just be me-
What gets me is that the people who should be most concerned about grams, endurance racers, are starting to turn to much bigger tires in the form of 29ers. This is the group for whom those extra grams REALLY add up to LOTS of spent energy through accelerations and climbing. The success of 29ers in endurance racing should really put this "big slow" wheel issue to rest.
A larger diameter wheel changes the effective gearing. This is where the perception comes from. You wouldn't be afraid to add larger rings to a 24" bike. Why be afraid of switching to smaller ones for a larger wheels?