Originally Posted by moxfyre
Wow! That's a great site... I wish more people knew about it. I am still slightly confused, because I have heard from knowledgeable people that rolling resistance DOES decrease between, say, 35 mm and 25 mm. But I guess that site only considers the difference between 23 mm and narrower tires.
There are two reasons why a 25mm tire might have lower rolling resistance than a 25mm tire.
1. The 25mm tire may have a higher maximum pressure rating that results in a smaller contact patch than the wider tire.
2. The 35mm tire may have tread features or other construction details that are lossier than the 25mm tire.
Keep in mind that the general rule of wider tires having lower rolling resistance applies only for two tires of the same construction and pressure. The reason the wider tire would have lower rolling resistance is because it does not have to flex as much to make the contact patch. Tire features such as tread, stiff sidewalls, puncture resistance (kevlar belts) all generate losses as the tire flexes to create the contact patch.