Originally Posted by
Hermes
Great point on the tires. Larger tires have greater aero drag, a couple of watts, which is not insignificant over a long distance. However, if the ride is better and fatigue is less then the power production will be better trumping any loss. Also, the Tarmac may have stiff wheels contributing to the harshness of the ride. Manufacturers match framesets, wheels and components to the expectation of the rider. In many cases, riders buying carbon fiber bikes want a stiff ride or they think they do. The bikes are tuned to this market.
The deciding factor for buying the Cervelo R3 was the design of the chain stays and seat stays to absorb shock. It does a very good job plus it will accommodate larger tires.
C'Fool, unfortunately, the best advice I can offer is HTFU
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Are you sure that a wider tire has more aerodynamic drag. Bicycle tires have a rounded profile, a larger tire might offer a more aerodynamic (rounded) profile to wind, because the tire is more rounded, rather then being a flatter profile on a 23mm. There is rolling resistance, but IIRC that's not affected by tire width as much as once thought, but is more a combination of tire pressure, sidewall stiffness and load. Ride harshness also has a lot to do with tire pressure, if you run a 23mm tire at 130PSI, it will ride much more harshly then the same tire at 110PSI.