How did we broaden beyond looking mainly at aerodynamics for speed gains to consider factors such as rolling resistance?
Rolling resistance has always been there, and we’ve always looked at it. But not necessarily from the standpoint of the rim. It was mainly in terms of the tire. We didn’t look at how we could alter the rim. It wasn’t until the complete redesign of the 303 Firecrest that we started looking at how can the rim shape, tire-bed shape, all those things alter the four components of TSE (wind resistance, rolling resistance, gravity, vibration loss) for total system efficiency.
What did Zipp learn from creating the 303 Firecrest Tubeless Disc-brake wheelset, its first with a hookless rim?
Moving to the straight wall (hookless) rim unlocked something in rolling resistance that we didn’t necessarily know was there. The fact that the tire has a wider stance on a straight-walled rim compared to a crochet (hooked) rim helps with the tire’s shape, which ultimately affects the tire’s rolling resistance.
What is a simple explanation of rolling resistance?
Many things impact rolling resistance. How sticky the tire is will play into it, as well as the static friction of the tire to the ground. The factor that makes up a considerable portion of rolling resistance is the elastic hysteresis of the tire. In simple terms, it’s the tire deflection as you roll over it to create a certain contact patch—that deflection requires the tire to compress molecules. It requires plies within the tire to rub up against each other. All that extra movement within the tire creates heat, which is energy lost out of the system. We try to minimize the amount of movement within the tire to reduce those extra movements that happen, which essentially leach heat out of the system.