I’m not so sure about the numbers being reported at the wheels. It’s possible that wheel horsepower is reported, but even then I’d be surprised, since manufacturers would be more inclined to go with the higher number (bhp) out of salesmanship. Power isn’t multipled by the gears, so the only difference comes from drivetrain efficiency losses.
As for torque, the number at the wheels would be meaningless without the gear. (i.e. 150 lb-ft @ 3200 RPM in 4th gear).
Torque at the wheels is vastly different depending on the gear. The transmission keeps power (and thus work) constant, because it has to—the law of conservation of energy and all that. But it can negotiate the split between force and distance that goes in to making that work. That’s the whole nature of mechanical advantage.
In first gear, force is multipled greatly, at the expense of a lot of distance, so the engine spins a ton for little distance traveled. In fifth gear, distance is more important, so you can go 90 mph without needing a 40,000 rpm redline. The tradeoff is that you get less force multiplication. The point is that a lower gear will almost always provide more torque to the wheels at the same speed. That’s why downshifting works well for passing.
Let’s use my slow-ass Jetta as an example. If I’m cruising along on the interstate at 75 mph in 5th, I’m at my torque peak (3200 rpm). But if I want to accelerate as fast as possible, I put it in 4th (maybe even 3rd). Why? I make more torque at the wheels in 4th, even though the engine will make less torque at higher rpm. Here are the details for 75 mph:
Gear Gear Ratio Fin. Drive Engine Speed Engine TQ Wheel TQ
5th 0.80 3.667 3179 135 396
4th 0.97 3.667 3854 128 455
3rd 1.29 3.667 5126 112 530
The figures for torque at non-peak RPMs were guesstimated from a bad chart I found. But they’re certainly within a few percent. And of course, i ignored drivetrain losses in my calculations.
As you can see, at the same speed, I can generate a lot more torque (and thus acceleration) by dropping to a lower gear, as long as I’ve got room to run. Even though the engine’s torque drops off noticeably, I can generate significantly more wheel torque by downshifting. The torque dropoff could be much more severe and still alow me to benefit by downshifting.
And you mentioned tire chirp, which nicely illustrates my point. On my car, weak as it is, I can break the tires loose in first gear anywhere on the tach. Even far from the torque peak. But in a higher gear, not a chance. not even at the point of maximum engine torque. That’s because the wheel torque just isn’t high enough. As I showed above, in 5th gear, I get up to 400 ft-lb to the wheels from just 135 at the engine. But in first gear (3.45 ratio), I can get over 1700 ft-lb at the wheels. No wonder they light up!