Originally Posted by
msu2001la
UCI max tire width for CX racing is 33mm (for now... many assume this will change soon). I'm not sure there's a max width for road, so it comes down to aero/rolling resistance and weight.
Specialized could design a Tarmac that fits 38mm, but it's a race bike. There aren't road racing tires available in that size, and currently most racers are only going up to 28mm. A 28mm tire on a frame designed around 38mm would leave large gaps resulting in more aero drag.
I'm sure manufacturers work closely with tire (and wheel) manufacturers to plan for future products, so it's entirely possible that they're all working on aero bikes/wheels designed around larger tire sizes. I'm sure there's a point of diminishing returns on aero, weight and rolling resistance, but it's pretty clear that 23mm is no longer the sweet spot for that. Maybe it's 25mm? Maybe it's 28mm?
Yes, that's where I suspect things are going. The status quo isn't 23 anymore, but I suspect that it's those of us out on the road that will be testing ideas around rim & tire width before pros adopt it. Well that is unless someone has a "EUREKA!" moment that changes things so drastically that it gives a compelling competitive advantage.