Originally posted by Jimbo:
Acceleration (...the rate at which an object changes its velocity...) is always faster with the lower gears.
Well, Jimbo, there you go again, trying to play your word games to make it "sound" as though one option is faster when it's not always so. Let's look at the facts and how this all works.
Acceleration is a function of torque at the wheels. Torque at the wheels equals torque at the engine crank, less drivetrain losses, times gearing. For practical purposes, with the NSX (but not with all other cars), we can assume that drivetrain losses are a constant, and that torque at the engine is a constant. (When accelerating hard, torque at the engine actually varies up to roughly 20 percent, as you can see from
this graph, but that's less than the difference in gear ratios, so loss of torque due to the gearing loss in any upshift will be greater than the torque gained from the lower RPM, which is why you can assume that it's constant.)
Now, putting your statement in different words, the effect of the gearing on acceleration always goes in one direction (staying with our assumption that torque and drivetrain losses are constant). In other words, shorter gearing (which is expressed as a higher numerical ratio, also called "lower" gearing) always results in faster acceleration than taller (higher) gearing. That is indeed true.
However, it is NOT true that you will always (IOW at all road speeds) have shorter gearing (overall gearing, including the changeable gears as well as the R&P) with a higher ratio R&P. That's because there are some road speeds at which you will be in different gears with a higher ratio R&P. For example, assuming you've got a stock five-speed, with the 4.55 R&P, you will be forced to upshift to third gear at 72 mph. With the stock R&P, you can stay in second gear up to 81 mph. So, as a result, an NSX with a stock R&P can accelerate faster from 72 mph to 81 mph than an NSX with a 4.55 R&P. However, at speeds just below that range, both transmissions would be in second gear for maximum acceleration, and the 4.55 would be faster than stock; similarly, at speeds just above that range, both would be in third and the 4.55 would be faster.
As you accelerate from 0 to top speed with either of the two R&P, you go through various "speed bands" - some speeds at which the stock R&P is faster, and others at which the 4.55 R&P is faster. Again, as noted above, the primary benefit of the 4.55 R&P is at low speeds (below 40 mph) before you hit these "speed bands", and at high speeds (above 150 mph) when you're above them. In between, the bands pretty much even out. Which is why the 4.55 R&P really doesn't do all that much on the track, as you can see from the 40-110 and 40-140 acceleration figures.
Incidentally, the reason that the 4.55 R&P gives the
perception of being much faster than it is, is because the shift points are lower. Let's look at acceleration from 0 to 50 mph. From 0 to 40 mph takes 2.53 seconds with the 4.55 R&P, and 2.84 seconds with the stock R&P, yielding a benefit of 0.29 second for the 4.55. You upshift to second at 40 mph with the 4.55 R&P, but you keep accelerating to 45 mph with the stock R&P, which might take another 0.5 second. From 40 mph to 45 mph, the stock R&P is faster because you're in second gear, compared with third in the 4.55 R&P. The total time from 0 to 50 is 4.05 seconds with the stock R&P and 3.87 seconds with the 4.55 R&P, so the 4.55 gives you a benefit of 0.18 second. As you can see, the stock R&P is 0.09 second faster from 40 to 50 than the 4.55 R&P.
However, what you FEEL is how long you're accelerating
in each gear, not how long it takes you to reach a given speed. Accelerating to redline with the 4.55 R&P takes 2.53 seconds, and with the stock R&P takes maybe 3.4 seconds. As a result, it SEEMS like you have an advantage of almost a full second, because you notice when you upshift, not when you reach 50 mph. In fact, because redline occurs at a lower speed, your ACTUAL advantage is only 0.18 second.
