Lightweight Tires or Lightweight Frames in Bicycle Racing: Which one is Better

Similar to what you'd do for most types of wheeled racing, setting up a bicycle for competition racing involves concerns about overall weight. Many sanctioning organizations have strict regulations that limit the minimum weight of road and mountain bike frames. In spite of lightweight technology used to manufacture frames and components, racers and pit crews try to further reduce the weight of a racing bicycle.
Frames and Styles
Modern bicycle frames made from metal alloy and carbon fiber are engineered to provide structural integrity at the lightest weight possible. In today's market, you might find frames as light as 15 lbs., compared with heavier 19-lb. frames. For conditioned racers, a difference of 4 lbs. is typically not a concern, and frame selection is more of a preference.
Comparative Weight
Regardless of the minimal weight difference between lighter and heavier frames, the greatest amount of weight on a racing bicycle is attributed to the wheels and tires. If you stripped down a road bike or mountain bike to the bare frame, you most likely could lift the frame easily with one hand. If you held both wheels and tires in the other hand, you would find these are heavier than the bare frame.
Wheels and Tires
Road bike wheels are aerodynamically designed to provide minimum wind resistance by incorporating a narrow profile for narrow tires. Mountain bike wheels are designed to provide a stable platform by incorporating a wider profile for off-road tires. Manufacturers produce tires for each type of bike in two styles: clincher and tubular. Clincher tires mount in the same way as tubeless tires on a vehicle -- by inflating the tire so it seals against the inner edges of the rim. Tubular tires have an integral inner tube that provides inflation, making them comparatively heavier than clincher tires.
Applications
If you want the minimum weight on a particular road bike, you would combine narrow wheels with the lighter clincher tires. Typically, mountain bike racers are more concerned with reliability, and they select clincher or tubular tires based on a particular tread design or past performance record. Considering the limited amount of work needed to mount a set of tires compared with more exotic modifications, lightweight tires seem to be a preference in bicycle racing.