When you press start in the settings screen and bring up the horsepower and torque curves, I found the lack of labeling very annoying. I like to set up my gear ratios so that each consecutive gear falls into the torque band but I couldn't find out where my peaks (or plateaus in some cars' cases) started and ended.
In the chart we are given 3 known reference points. The game labeled a low and a high RPM. Also, HP & TQ are supposed to cross at 5252 RPM. Another given is the width of the black box; at least mine is 8.5" If your box isn't 8.5" wide, don't worry I will explain how you can work with your dimension. We're going to find out power bands with percentages and math.
Now the good stuff: How do we really find out what RPM everything happens at? Measure the black box from left to right; as mentioned before, my box is 8.5 inches. For simplicity's sake, suppose we are in a vehicle with a low RPM of 1000 and a high RPM of 7000. Put a ruler, or other measuring device on the screen. If you have a curved TV screen, the pliable ruler that a tailor/seamstress uses comes in handy.
Take a measurement on the line where you are interested. For example's sake let's say that I see a torque peak 3 inches into the box. The total measurement of the box is (your distance here) 8.5" for me.
3 (the measurement taken) divided by 8.5 (distance of overall box length) is 0.3529 or 0.352 rounded down. Thousandths are fine for our purpose. This is a percentage of the distance into that box.
Remember your difference in RPM? If not, subtract the low labeled RPM number from the high RPM. For this example our result is 6000 (7000-1000); that is the 6000 RPM span of unlabeled space in the black box. If you multiply 0.352 by 6000, you end up with 2112. This answer is the RPM where we took the measurement.
We can now deduce that at 2112 RPM, we have found the torque peak we were interested in. Why is this helpful? Cars have listings of their power peaks (317 HP @ 5600 RPM for example) but more often than not there is more usable RPM that the game doesn't mention. Many vehicles from Audi (and some turbocharged cars) have flat power bands. These are great because in their case, power is usable through a wide range of RPMs and we don't have to answer the question we just solved for. We can set our gears up to match the power that the game lists.
Hope this helps people.