Brake Test Results
5 years ago
Brake Pads Tested
A Brake Pad Shakedown
A highly specialized product typically excels at one specific task. As a general rule, when you ask this component to perform a wider variety of functions, it cannot accomplish any one of them as well as if it had a singular focus. We see this when talking about tires - if you want the fastest possible lap time around a race track, choose a Racetrack & Autocross Only tire. Need that tire to achieve some level of wet traction or the ability to drive you to and from the track? A Streetable Track & Competition tire can do those things, but your lap times won't be quite as fast. And what if you need a greater level of wet grip and would like to get maybe 12,000 miles out of your tires? An Extreme Performance Summer tire fits the bill, but you're looking at another step backward for track performance. Now, you say you need excellent hydroplaning resistance and want to shoot for 20,000 miles or more? A Max Performance Summer or Ultra High Performance Summer tire can accomplish those tasks, but they're not intended for track use. What if you need these tires to get you to work on a snowy day, too? It's easy to see where this is headed.
The unfortunate reality is that no single product can optimally perform on the street and on the track. It will either be severely compromised for one or the other, or moderately compromised for both. Brakes are not exempt from this reality, and knowing this, our customers often ask what sacrifices they should expect to make when driving a street-oriented brake pad on the track, a track-only compound on the street, or a combination street/track pad in both situations. To gain a better understanding of the give and take involved with differing pad designs and compounds, the Tire Rack team underwent a modified Real World Road Ride and Performance Track Drive. In an effort to control the conditions, both portions of the test were performed on our track.
The test vehicles were our fleet of 2014 BMW F30 328i Sedans. Knowing springtime weather in northern Indiana can vary drastically and change at a moment's notice, we needed a tire that could provide enough traction to challenge the brakes under a variety of driving and temperature conditions. To this end, all vehicles were equipped with brand-new 245/40R18 Michelin Pilot Sport A/S 3+ tires with break-in miles only. The Pilot Sport A/S 3+ is the successor to Michelin's category-leading dry and wet performer, and we were confident in the tires' ability to smartly slow the test vehicles, no matter the weather. The brake pads were also brand-new and matched to sets of identical rotors on all three vehicles, with the proper bed-in procedure performed before testing.
*The Mu factor represents a measurement of the brake pad's coefficient of friction against the brake rotor surface with 0 representing no friction and 1.0 equal to no movement at all. Because the Mu factor changes with brake pad temperature, the curve developed across the normal operating range will represent the pad's expected performance level on the vehicle.
Braking In Everyday Life
To simulate typical, urban driving, the Tire Rack test track was divided into four separate zones, each marked with a different speed limit from 20-40 mph and divided by stop signs. Our testing procedure entailed briskly accelerating to the posted speed limit, then leveling off and maintaining that pace before coming to a smooth and controlled, complete stop representative of the type of braking one would perform in the real world. Each tester was instructed to complete two laps of the course using the BMW equipped with each brake pad.
The first product our drivers tested was the Hawk High Performance Street (HPS) 5.0. True to its intended purpose, the HPS 5.0 felt well integrated with the BMW factory brake system. The effort required seemed perfectly linear, with every increase in pedal pressure met by a commensurate increase in braking force. This linearity allowed for easy modulation, and the driver could instinctively dial-in the exact amount of input necessary for a smooth stop from any speed. Noise was nearly non-existent when the pads were in the temperature range typically experienced during street driving, and the level of brake dust was minimal. Coming as no surprise, the HPS 5.0 represented a well-mannered and civilized option for use on a daily-driven vehicle.
The change in personality when switching from the HPS 5.0 to the BMW equipped with the High Performance (HP) Street/Race pads did come as a surprise, however, catching many of our testers off-guard and resulting in initial stops well short of the intended braking zone. The HP Street/Race is a lightly modified racing brake pad, and the compound used in the pad requires very little pedal pressure to generate high clamping force, resulting in a brake pedal that feels "grabby" if the driver is not prepared. Once acclimated, however, the driver can adjust to this characteristic and will be treated to authoritative stopping power from brake pads that bite immediately and hang on with vise-like grip as the coefficient of friction seems to increase exponentially with added pedal pressure. A side effect of this monumental stopping power comes in the way of noise and dust, a considerable quantity of both when the brakes are at normal street temperatures. Nearly every driver reported squeaking and squealing during their simulated road ride, and many indicated grinding, as well. A typical track day aficionado is likely to accept this disruption as a necessary trade-off for the capability to stand up to repeated high-speed stops, but someone who is simply an enthusiastic street driver may find it off-putting if they have to frequently wash corrosive brake dust from their wheels and when the noise emanating from their brakes turns heads in the grocery store parking lot or when stopping at a red light.
Using a track-only pad like Hawk's DTC70 on the street is comparable to driving a racing slick in the rain. It wasn't designed to excel in the situation, and the results are predictable, so we were expecting little-to-no stopping power when the pads were cold. What could arguably be considered the biggest surprise of all came when driving the DTC70-shod BMW because the car actually stopped. From when the brakes were stone cold for the first stop of the day until the completion of the final lap, no tester reported any concern stemming from the brakes' inability to slow down the vehicle in time. Required pedal effort was higher than either of the streetable pads, and the initial bite was about the same as the HPS 5.0, but from the perspective of feel and stopping power, the DTC70 pads were surprisingly average in our "street" test. Where these track-only pads stood out, however, was the level of noise, dust and rotor wear produced during our two days of street testing. Every one of our testers found the DTC70 pads to squeal, grind or both in the conditions to which they were subjected during our simulated road ride, and as expected when using a racing brake pad in an environment it was never intended for, the rotors wore at a rapid rate. In one day of testing, and with speeds never exceeding 40 mph, the front rotors used with the DTC70 brake pads lost 23% of their usable thickness, with another 14% lost during the second day. At that wear rate, someone using these pads on their daily-driven vehicle could expect to replace their brake rotors approximately once every month.
Braking at the Track
For the "track drive" portion of the test, the Tire Rack test track was again utilized, albeit in a different configuration. The northern half of the track was sectioned off into a high-speed loop with three distinct braking zones. Top speeds were still modest at approximately 60 mph, but the steady stream of testers cycling through would ensure heat was maintained in the braking system of each vehicle.
Day One brought with it steady rainfall, certainly not ideal conditions for a braking test. Even though the Michelin Pilot Sport A/S 3+ tires on the vehicles boast some of the best wet-weather performance available in the all-season category, because of the higher-than-normal speeds and intermittent wet, the decision was made to disable traction control while leaving the vehicles' Electronic Stability Control activated. This is where things took an interesting turn.
Electronic Stability Control (ESC) utilizes a yaw sensor to detect lateral slip of the vehicle's rear end. If the system recognizes too much sideways movement in the back, it will apply the rear brake on the appropriate side of the vehicle to counteract this slippage and keep the car pointed straight ahead. Under normal, dry conditions, the system rarely engages in any but the hardest of street driving. In the wet or snow, ESC is more active, but still with relatively infrequent intervention. While driving our modified track's high-speed loop in the wet, though, ESC was working overtime. As is recommended during any performance driving, each vehicle's brakes were inspected during a mid-day break on both track drive days to monitor wear and ensure sufficient friction material remained to complete the second half of each day. Removing the rear wheels from the DTC70-equipped BMW revealed that as a result of the still too cold operating conditions and the ESC's consistent application of the rear brakes, the pads on the rear axle had worn down to the point of being alarmingly close to the backing plates. Nothing unexpected was revealed when the HPS 5.0 pads were scrutinized, but the rear HP Street/Race pads showed significant wear as well, if not to the extent of the DTC70s. Based on the condition of the brakes, it was determined the vehicle with the HPS 5.0 pads would continue as is, since there was little-to-no perceptible wear of the pads or rotors. The HP Street/Race car was determined to have adequate remaining friction material to complete the test, but would require regular visual inspection of the rear pads. For the car with the DTC70s, there was no choice but to perform an emergency rear pad and rotor replacement, so it was fortunate we planned ahead and had spares.
Day Two of our track drive brought clear skies, and with them the promise of ideal testing conditions and no surprises. Thankfully the weather delivered on its initial promise, and we were able to develop some insights of each pad's performance in a dry track setting.
Mirroring its performance during our street drive, the HPS 5.0 provided confident stopping power with a firm, easily modulated pedal. The consistently elevated temperatures encountered during this portion of the test were not ideal conditions for the most street focused pad of the group, and some testers reported a moderate increase in noise levels and slight, but perceptible fade.
The HP Street/Race proved its racing pedigree when put through the rigors of the track drive. The strong initial bite and light pedal pressure found favor with our testers, and braking was easier to modulate thanks to steady pedal input resulting in a ramp-up of stopping power that was more linear than we experienced on the street. Further evidence that the HP Street/Race leans slightly more toward the race side of the equation is our drivers gave it a better score for noise at the track than on the street, and the least amount of daily rotor wear occurred during the dry track test session.
Even with the consistent, relatively high-speed braking on our course, we were just beginning to enter the lowest end of the DTC70's intended operating temperatures. Considering how far out of its element it was, it put forth a good showing, receiving positive subjective ratings from our test drivers for initial bite and fade resistance. Quite telling were the scores for required pedal pressure and ramp-up. The DTC70 pads' ratings indicated they required the least pressure to obtain the desired amount of braking force, and when maintaining steady pressure, the stopping power had the greatest increase. During each driver's brief stint behind the wheel in our test, this fact is not particularly significant. However, in the DTC70's intended application, the race track, where a driver may spend hours at a time behind the wheel and every ounce of energy and concentration is precious, this combination would be preferable to a pad that requires the driver to stand on the pedal every time he or she wants to slow the vehicle.
In addition to the modified Performance Track Drive, we also intended to perform our standard instrumented 50-0 dry stopping distance metric with each brake pad to conclude the test, and fortunately mother-nature gave us consistent conditions from the first stop to the last.
In the 50-0 ABS stop, the HPS 5.0 unsurprisingly felt the most in-tune with the Michelin Ultra High Performance All-Season tires and factory antilock brakes, returning the shortest average stopping distance of the group by a modest margin of 3.5 feet. Our instrumented brake testing placed the HP Street/Race and DTC70 in a statistical tie objectively, but the subjective feel was quite different. It was apparent the engineers at BMW did not anticipate the use of such aggressive pads when they calibrated the vehicle's antilock brakes, and despite the Michelin Pilot Sport A/S 3+ tires' impressive performance credentials, they could not match the immediate initial bite from the Hawk HP Street/Race pads. As a result of this combination of factors, when the brake pedal was forcefully applied to simulate a sharp panic stop, the brakes would momentarily overpower the available grip from the tires, causing brief but discernible tire lockup as the ABS computer struggled to catch up and modulate the braking force. Though this phenomenon only lasted a fraction of a second, it was consistent and repeatable, leading to the conclusion that for balance and to optimize performance gains, the HP Street/Race may be better paired with a tire from the Max Performance Summer category or higher. The objective braking numbers produced by the DTC70 were equal to the HP Street/Race pads, and the DTC70 felt nearly as well integrated with the factory braking system as the HPS 5.0, but that does not mean the DTC70 should be used on the street. In our four days of testing, the rear DTC70 pads and their corresponding rotors needed an emergency replacement, the front rotors lost 64% of their usable thickness and the front brake pads wore through almost 30% of their total friction material. Without the amount of heat encountered in a real track environment, a driver using Hawk's DTC70 track-only pads would experience incredible wear rates of two major components in the vehicle's braking system.
With their HPS 5.0, HP Street/Race and DTC70 brake pads, Hawk has produced three products with distinct and clearly defined personalities. This makes determining the correct choice for your needs simple and straightforward, with nothing more than a little introspective thought required.
Is your vehicle a daily driver that never sees track use, or if it does make it out to the race track are you unwilling to sacrifice on-road civility for increased performance on the track? If so, the HPS 5.0 is likely the pad for you.
If you have a combination street/track vehicle and you're OK with increased noise and dust in exchange for confident on-track capability, then the HP Street/Race should be strongly considered.
And if you trailer your high-powered race car to the track, the DTC70 may be your best option.