AutoEuphoria
Captain Slow
Not that anyone here would want one, but it's still interesting.
http://www.caranddriver.com/feature...mo_z_s_brakes_failed_at_lightning_lap-feature
When we last left off, we had just embedded a Nissan NISMO 370Z into Virginia International Raceway’s Turn One retaining wall during our fourth Lightning Lap [February 2010] so forcefully as to have fused them together into a sort of vehicular diphthong.
The cause? It certainly wasn’t a case of running out of talent. No—fact is, the NISMO’s presumably strong brakes weren’t. And they failed us at the worst possible time—at the fastest point on the track, when we were attempting to decelerate from 130 mph for the 45-mph right-hander that is Turn One.
What was unnerving to this driver, having just survived the most terrifying experience in a 15-year driving life, was that Nissan officials from Japan weren’t at all surprised. They matter-of-factly reported that the Z’s stock brake pads were designed primarily for low noise and low dust, and not for racetrack situations. It’s our view, however—and we don’t think we’re alone—that the NISMO Z, an even sportier version of a sports car, should be equipped with brakes competent enough to survive a few hot laps. And it’s worth noting that we’ve never experienced such hellacious brake degradation in the history of our Lightning Lap events.
As a result of our crash, Nissan began offering high-performance brake pads as a $580 option for any Sport package–equipped 370Z or NISMO Z.
We wanted to test the fortitude of these upgraded brake pads for ourselves, so we arranged a back-to-back test of the base pads—like the ones on our Lightning Lap NISMO Z—and the new pads. We used two Sport-package 370Zs (which have the same brake hardware as the NISMO Z). To provide as much context as possible, we employed the same severe methodology from our 11-vehicle braking showdown [“The Power to Stop,” August 2008]. That consisted of a continuous battery of stops from 100 mph until the performance of the brakes degraded significantly. These 100-mph braking events were broken down into five-stop cycles; we began each cycle with a moderate, 0.5-g stop (that’s about half of the Z’s ultimate braking capability) and measured brake-pedal force and travel for evidence of fade. Four panic stops followed each cycle’s first moderate stop, and we recorded the distance it took the car to come to a standstill. We executed stops every 20 seconds (including the time to accelerate back to 100 mph) and repeated the five-stop cycles until the brakes succumbed to fade. That’s when the brakes get so hot that it causes a reduction in the friction between the pads and the rotors, which leads to longer stopping distances and increased pedal travel, as well as requiring more pedal force.
Typically, a sporty car can endure 30 or 40 stops in this fashion, but after seven strong panic stops, the base Akebono pads began to give way, which wasn’t surprising given our Lightning Lap experience. Stopping distances from 100 mph worsened from about 325 feet to nearly 500, a level the Z maintained through cycles two and three. By the end of the fourth cycle (or 20 stops), braking distances stretched to more than 1000 feet, pedal travel increased by almost four inches, and even goading the pedal with 150 pounds of force couldn’t produce 0.5 g of deceleration. Although the brake-pad fade was dramatic, at least it happened somewhat gradually, far more so than during our wild ride at the Virginia track.
These pads fall into the “non-asbestos organic,” or NAO, category found on most street cars, and those organic materials simply can’t deal with racetrack levels of heat. The base Z’s pads melted away—no exaggeration—to practically nothing during our 10 minutes of flogging, depositing their material around the rotor in what at first glance appeared to be significant scoring.
The new, upgraded pad (branded NISMO) is sourced from Federal Mogul’s Ferodo line (no Hobbit jokes), which also halts impressive machinery such as the Ford GT, the Chevy Corvette Z06, and the Lamborghini Gallardo. This pad material is referred to as “low-steel,” a category generally defined as being comprised of 10 to 25 percent steel fibers. The steel helps the pads remain effective at high temperatures, and although the pads were designed for track use, Federal Mogul says noise and dust behavior were significant considerations in the pads’ construction.
These brakes had noticeably more bite—initial stopping distances were about 10 feet shorter than with the base pads—but an argument could be made that, overall, this setup wasn’t necessarily a step in the right direction. Although the upgraded pads endured roughly a dozen more stops than could the base pads and were extremely consistent—the Z’s 20th stop took 318 feet, almost exactly the same as the first one—their performance fell off a cliff shortly thereafter.
The next two stops were spooky: Mashing the brake pedal caused the Z to veer quickly and dramatically, requiring steering correction to keep it in a straight line. A likely cause of the unbalanced braking forces that produced this yaw is brake fluid boiling at some corners of the car but not at others. The next stop fully boiled the fluid and caused the braking force to evaporate completely—the pedal sank to the floor as we sailed on for almost a half-mile in what felt eerily like a repeat of our racetrack crash. We now feel certain that boiling the brake fluid, which was probably made easier because most of the pad material had already melted away, is what caused the brake failure and subsequent crash at VIR.
However, unlike the Virginia experience with the base pads, the new pads were largely unfazed by the two-dozen stops from 100 mph. It was just a matter of trying to get the calipers to squeeze the pads tightly enough; pumping frantically at the brakes to overcome the fluid issue continued to provide stopping power.
And so we decided to conduct a test we hadn’t planned: swapping the Z’s standard brake fluid for an aftermarket product, ATE Super Blue, which has a higher boiling point (536 degrees F). We tested the fluid, which goes for a little over $6 a pint versus about $5 for the stock fluid, along with a fresh set of brakes with the upgraded pads. Considering 23 essentially fade-free stops, not only did the fluid extend braking performance, but stops 24 through 31 showed gradual fade—a warning to the driver that things are starting to overheat—which made this by far the best setup. After that, even the ATE fluid couldn’t persevere, and it, too, boiled.
Although the upgraded pads and the one-step-up fluid much improved the Z’s braking, even this best performance was closer to the less-track-oriented BMW 335i’s from our previous braking test—although the BMW never boiled its fluid—and quite a ways behind the sports-car champs, the Corvette and the Porsche 911, which both survived more than 45 stops with minimal fade and no failure.
So where does the fault lie with the Z’s overheating brakes? It’s certainly not with the brake hardware itself. Comparing the diameter and thickness of the Z’s vented rotors—14.0 x 1.3-inch fronts and 13.8 x 0.8-inch rears—with those of the competition reveals that they are far from inadequate. In fact, when factoring in curb weight, the 3400-pound NISMO Z is much better endowed than a Mustang GT Track Pack or a Hyundai Genesis coupe with the optional Brembos. The NISMO is on par with a Chevy Camaro SS—whose brakes performed admirably at the latest Lighting Lap—and is only slightly less stout than the nearly indefatigable Corvette Grand Sport. Part of the reason for the relatively large rotors is that this Nissan brake hardware is used on bigger and heavier vehicles such as the Infiniti M sedans and FX SUV.
The fault cannot be pinned on the brake fluid, either. Nissan’s DOT 3–grade fluid, which is used in everything except the GT-R, has a dry boiling point of 450 degrees F. That’s identical to that of GM’s DOT 3 fluid, which is used throughout most of the General’s lineup, including Corvettes, but is not as extreme as VW/Audi’s 509-degree DOT 4 fluid. So while our test with the aftermarket brake fluid extended the capability of the Z’s brakes, it couldn’t solve the heat-buildup problem—it simply staved off the inevitable. Thus, an even more expensive and sophisticated fluid with a higher boiling point wouldn’t be a panacea, either.
Our suspicion is that Nissan got a bit greedy in its quest for today’s all-important fuel-economy numbers and boosted the Z’s aerodynamics a little too far by cutting back on the amount of air directed through the wheel wells to cool the brakes. Key takeaway: If you intend to track a Z, don’t use the base pads, upgrade the brake fluid, and be sure to install brake-cooling ducts.
http://www.caranddriver.com/feature...mo_z_s_brakes_failed_at_lightning_lap-feature
