Sum, Scott is right. There is a simple mathematical relationship between torque, rpm, and horsepower. Horsepower is torque times rpm. Yeah, you divide it by 5252 to scale the result down to match what Watt's horse could do, but conceptually, you can think of horsepower as torque times rpm, i.e. the combination of the two. As I previously showed, torque and rpm are interchangeable entities that make equal contributions to performance, therefore they're weighted equally in the horsepower formula.
The 5252 scaling factor comes from the fact that Watt's horse could lift 1lb 33,000 feet in 1 minute. Well, 1 lb-ft of torque is defined as 1 lb of rotational force at a 1 foot radius. 33,000 feet is how far that 1 foot radius travels if you make 5252 rotations (r x 2 x pi x 5252 = 33,000). So 5252 rotations moves that 1 foot radius point 33,000 feet. If it has 1 lb of force on it and it does those 5252 rotations in 1 minute, it's doing exactly what Watt's horse could do and we call it a horsepower.
In any event, the important point is that the power peak rpm is always where the combination of torque and rpm are at their greatest. If you go to a higher rpm than the power peak, the torque will drop more than the rpm rises, hence you have less horsepower.
My point here is that it's physically impossible to rev the motor past it's power peak, and then with gearing, end up with some higher combination of torque and rpm. The power peak is where you want to be when the wall of air stops your acceleration, because that's where you're getting the most out of the motor. You can't get more with gearing tricks.
That's what you want to do to maximize rear wheel torque at a given rear wheel rpm. The difference between that and force at the contact patch is a function of the radius of the tire. But it scales linearly, there's no free lunch. A shorter tire reduces ground speed by the same factor that it increases contact patch force, and vice-versa.
That said, I think I misunderstood what Sparky is doing. From his later post, it seems he's really effectively adding resolution to his gearing selection by considering tire size in conjunction with axle ratios and power available on each side of his power peak. Basically, since he doesn't have infinite resolution in gear selection, there's a range of rpm he's forced to work over, he can't always gear right for his power peak. His available axle ratios and tire sizes define that resolution for him. Anytime he's not right on his power peak, he's going to have less than optimum rear wheel torque, but that may be outweighed by being able to get closer to the wall, which of course is the name of the game.
