Before we close the book on this series, or decide to go off on some crazy tangent like pulling the trigger on a warranty-blowing power upgrade--interesting thought--we recently performed an additional test that you may have a great deal of interest in.
Most car enthusiasts will participate in driver's schools and track days--I'm totally hooked myself. If your days at the track exceed three or four per season you probably want to purchase a set of dedicated wheels and tires so you can save your expensive street tires for everyday use. Of course, the other reason is to improve hot grip to get through the corners more quickly. Nitto Tire provided Project Z4 M with a set of NT01 DOT-legal, R-compound road racing tires, sized 245/40ZR18 for the front and 275/35ZR18 out back.
The NT01 is designed with an asymmetrical, non-directional tread pattern for easy rotation on either standard or staggered setups, and it has an extremely large outer shoulder to maximize the contact patch under heavy cornering. Nitto manufactures this tire with a high modulus rayon carcass and body ply construction for maximum lateral and high-speed stability. Tread depth is 6/32 of an inch and it can be shaved to 3/32 to reveal a "slick" tread surface with two circumferential tread grooves. It also features a specially formulated rubber compound for hot on-track performance, which delivers extreme cornering grip for faster and more consistent lap times.
After putting in a couple of proper heat cycles a few days before, and sufficiently playing with the hot tire pressures (40 psi seemed to work best in our track conditions), we felt it was time to put the NT01 to the stopwatch by means of our Traqmate GPS acquisition system. As usual, we attempted to be as consistent as possible testing with similar weather conditions, the same driver, and no in-car time displays as we've done for all previous track tests. The NT01s proved themselves admirably throughout our testing under dry conditions. Turn-in and feedback were precise and reliable. Cornering grip was astounding, while at the same time their breakaway felt progressive and forgiving. They also exhibited excellent consistency throughout the day even as the track temperature fluctuated, and they did not get "greasy" toward the end of a longer session when hot tire pressures were properly managed. Lap times were 1.5 seconds faster at our two-mile test track than baseline laps run previously with the Nitto Invo street tires in the same sizes (88.05 seconds compared to 89.55). The figures to the right show a speed versus distance comparison of the NT01 and the Invo along with an accompanying cornering force versus distance plot. Higher corner speeds and greater cornering g-forces are prevalent with the NT01 R-compounds.
This project has really been all about the numbers. We swapped out carefully chosen aftermarket tires, wheels, brakes, suspension components, air filter, and the entire exhaust system, along with a front strut brace and a pair of front camber plates. Along the way we demonstrated these mods' efficacy through controlled GPS track testing, and on the dyno in some cases. We collected a mountain of numerical data, much of which we've shown throughout the series, and we've been rather pleased with and even surprised by the results.
The table on the next page shows the progression of decreasing lap times with each new modification. Note that we have also tracked the power gain at the wheels as well so we can easily point to where the added speed is coming from. Notably we were able to "double dip" with grip and power in Part 2 with our lightweight wheel and tire upgrade. It's also interesting to see that the final 29hp power upgrade didn't reduce lap times as much as the individual handling modifications. However, the increased power and low-end torque made the car much more lively in all conditions and is easily felt from the seat of the pants.