Originally Posted by
Pugsly
A fatter tire has much higher rolling resistance so will slow you down. That's why running your tires at lower pressure slow you down (it's not, as you would argue, the slightly reduced radius)
If I'm reading you correctly, you have it mostly wrong. If there existed a 35mm tire that could hold the same pressure as a 23mm tire, the rolling resistance would make very little difference in speed. It's the lower pressures that result in the wider tires being slower.