Originally Posted by
SweetLou
Well, that is not scientific either, though I don't think you meant it to be. The difference in speed is caused by many factors. You and your bike weighing less is actually to your advantage. Because of the smaller amount of mass, you have less inertia. This means it is easier to change, in this case it would be your speed. The smaller wheel will also have less rotational inertia, allowing it to start faster, but there are other factors, like the rolling resistance of the tires. Since the tires are not the same, then the rolling resistance is not the same. Even tires that look the same can have different rolling resistance. The friction of the hubs also needs to be overcome, your bike might be tuned better.
700c wheels have a greater rotational inertia than 26" wheels. 26" wheels are easier to get up to speed whereas 700c wheels want to stay at that speed better.
This is not true. If a 700c tire and a 26" tire of the same width and equal pressure will have the same contact patch. The contact patch is determined by the air pressure and the total weight. When the contact patch x air pressure = weight, the tire stops deforming.
Wide tires have less rolling resistance than thinner tires at the same pressure. Though the contact patch will be equal, the thinner tire has a longer patch. This means more sidewall length needs to deform, this causes a greater rolling resistance. Though wider tires at the same pressure have less rolling resistance, most wide tires are of smaller air pressures, which means that a longer patch is needed to equal air pressure and total weight. This causes greater sidewall deformation causing greater rolling resistance. The sidewall strength is also a factor in rolling resistance. If a tire's sidewall is made to easily deform, there is less rolling resistance.
Rolling resistance is not a function of wheel size, it is a function of tire width, air pressure and sidewall strength.
I really want to let this go, but I have to point just a few things, and then I'm done... really!
--Lighter bikes change direction more easily when acted upon by an outside force. This is true, but it's a little different when rolling down hill. Now we're talking about potential energy and the object with greater potential energy will accelerate faster unless friction overcomes the difference.
--My wheels are 700c and lighter by 300-400 grams than his, so my wheels have smaller rotational inertia.
--Tire compound - yes, this is a good point! Is it enough to make up for 40lb advantage?
-- Tire size -- we were about equal in that department. His are 25c with a round profile and mine are 28c but run narrow.
--My hubs are road hubs which are more efficient. My wheels are larger and roll over road imperfections better. Blue Ridge Parkway, where we repeated this amazing feat time and time again, is anything but smooth, but the views are spectacular!