Originally Posted by
Myosmith
"Fast" bikes are generally lighter, stiffer, and have a more aggressive geometry and some aerodynamic considerations. The engine is still the number one consideration. Building fitness while dropping excess bodyweight will make a big difference. If you play with the online calculators you'll see that weight primarily comes into play uphill and during sprints. On flat ground the difference in watts needed to maintain 20 mph for a 250-pound rider/bike isn't all that much more than for a 180-pound rider/bike. Add an incline or try to accelerate and the numbers quickly favor the lighter combination.
A personal amusement is watching a rider who is 30+ pounds overweight drop big money on titanium pedals and a carbon fiber seatpost to make the "bike" faster.
Sure, when I bought the Tricross I was aware it had the exact same problem the Rockhopper had, namely it needed a better rider. What I found interesting was the difference in handling between bikes when the engine (i.e. me) was the same, and wondering which components of the bike made up the biggest parts of that difference.
I figure if you put me on an all-out speed machine and someone like Mark Cavendish on a mountain bike with a slightly inaccurate saddle position and lumpy tyres the chances are I'll get smoked like a kipper. But when you put me on one bike and then put me on another bike the engine issues are removed from the equation.