Stoptech Brake Upgrade for Jetta IV

A stock Jetta 1.8T is generally a fun-to-drive car around town. Its brakes offer excellent feel with strong initial bite. However, those who have driven one on a racetrack or taken it down their favorite mountain road know that the stock brakes quickly heat up and fade when asked to endure heavy labor. Just as much as a chip and standard breathing improvements do, extending the Jetta's initial braking performance to the tenth lap or the bottom of the mountain would make the car a more rewarding drive.

Fortunately, big-brake options abound for this car. There is the TT upgrade for five-lug cars, of course, and practically every performance brake company has some option for the latest Volkswagens. Some enable the use of Porsche hardware, which will impress the heck out of most onlookers. Among the best is one sold by Stoptech, a relatively new company that ec had heard of but knew little about--until recently.

It all started when I got a call from a representative of Boston Acoustics, inviting me to witness Stoptech's testing as it put the company's big-brake kit on Boston Acoustic's Jetta. It turned out that Stoptech tests in the same location ec does, so I simply arranged for the Jetta to show up on the same day we planned to be there. What I saw, and learned later by visiting Stoptech's headquarters, was most impressive. It turns out that Stoptech, though a new player, is a truly innovative company doing real research and development, offering a product of superb quality. Stoptech is about much, much more than just brakes that are bigger and fit on the car.

Fundamentally, big brakes should improve a car's performance. The weight they usually add, as well as the financial cost, are too high to justify putting parts that don't work properly on a car. That statement leads to the question: What performance are they going to improve? Using the stopping distance from 60 to 0 mph as the standard measure of a car's braking performance isn't all there is to it, since the shortest stopping distance a car can achieve from 60 mph is at least as much a function of tire and suspension performance as of braking performance. More important is consistency, repeatability, resistance to fade, durability and longevity of the system and balance. The ability to slow the car safely, time after time from high speed--never causing the driver worry, with no chance of locking the rears and causing a spin--is what really matters. Some people may get uptight about noise and brake dust, but that's mostly a function of pad choice, and driving enthusiasts are usually more than willing to compromise in those areas.

Brakes accomplish their task by the seemingly simple route of converting kinetic energy to thermal energy (heat) and dissipating it to the atmosphere. To do this well, they must have the thermal capacity to absorb a great deal of energy while slowing, and the ability to dissipate that heat rapidly. As well, brakes must continue performing well at the high temperatures that maximize the rate of heat dissipation.

Stoptech provided a dramatic demonstration of these principles when it installed its kit on the Boston Acoustics Jetta. I witnessed before and after testing, a series of six or seven stops from both 60 and 80 mph. Not only was stopping distance recorded, but front and rear brake rotor temperatures were measured. After testing the Jetta with stock brakes, Stoptech's engineers pulled the car off to the side, installed their own brakes in just a few minutes with hand tools, and repeated the testing.

The car showed up ready to test with 8mm H&R Trak+ spacers installed, enabling the existing aftermarket wheels to clear the big calipers. In the rear, 15mm spacers were used because the owner of the car preferred the look of the wider track. With Volkswagen's uncomplicated rear suspension design, thick spacers are unlikely to cause any problems, though Stoptech was careful to recommend the use of properly designed wheels if possible. Fewer, simpler components make a better system.

From 60 mph to a stop, the Jetta showed that this standard test is not as demanding as it is commonly purported to be. Chart 1, (Rotor Temperature, 60 to 0 mph) tells the tale. After six stops, rotor temperatures were continuing to climb, while Chart 3, (Stopping Distance) shows that stopping distance remained stable. The stock brakes were able to cool adequately on the turnaround and run-up to 60 mph. This, in itself, suggests Volkswagen engineered the Jetta's brakes to perform more than adequately for the vast majority of drivers pretty much all the time.

Chart 2 (Rotor Temperature, 80 to 0 mph) shows another story. After the first stop, rotor temperatures were higher in the front and rear than they were even after the sixth stop from 60 mph. Rotor temperatures stabilized after the fourth stop, with the fronts near 1050*F, and the rears a little over 800*F. Meanwhile, as we see in Chart 3, stable rotor temperatures correspond to a significant rise in stopping distance, from about 215 ft to around 235 ft. This indicates that the brakes were just too hot to work anymore. The friction material could not perform. It's coefficient of friction decreased significantly, and it simply couldn't change the car's kinetic energy into thermal energy in the rotors.

In both sets of stops, the temperature of the front rotors was significantly higher than the temperature of the rear rotors, indicating that the load was unevenly distributed. The stock front brakes were doing significantly more than their fair share of the work to stop the car. It's something of a mystery why this was done, as the Jetta has four-wheel anti-lock brakes, making it very difficult to lock a rear wheel and cause instability.

With the Stoptech brakes installed on the front of the Jetta, performance was enhanced significantly. On the first stop from 60 mph, Chart 1 shows that the front rotors were cooler than even the rears with the stock setup, while the rears were hotter than stock. Essentially, the large Stoptech rotor was showing its high thermal capacity and absorbed the heat from the stop without increasing much in temperature. By the third run, I could see what the situation was going to be. Front rotor temperatures were significantly decreased, while the rear rotors were much hotter than with the stock setup, almost as hot as the stock front rotors had been. Clearly, the rear brakes were being made to do a lot more work, in spite of the increased size of the fronts. The peak temperatures reached were roughly 150*F lower than stock for the front, and about 100*F higher than stock for the rear. From this, we can see that Stoptech moved the brake bias rearward. Did it go too far? I would have to wait for the 80-mph tests to find out. As you might guess, the stopping distances from 60 mph were extremely consistent, traction limited at almost exactly the same distance as with the stock setup. If we had performed only the customary 60-mph magazine braking tests, it would appear that Stoptech's brakes, though they looked cool on the car, had done nothing to improve performance. By taking rotor temperatures, however, I could see there was something else going on.

The real story is told in Chart 2, showing the temperature data in the 80-mph stops, where all the aerodynamic work done by Stoptech to optimize cooling of the rotor showed its worth. With the Stoptech brakes installed, rotor temperatures were closer together than stock, but the rears were running hotter, both just slightly higher than on the seventh stop from 60 mph. As we continued to abuse the brakes, the front rotor temperatures finally surpassed the rears, but only by a little bit. Both front and rear temperatures finally stabilized after six stops from 80 mph. The rears, still doing more work than stock, were only about 60*F hotter than in the stock configuration, while the temperature of the front rotors was down approximately 120*F from stock. Adding the Stoptech setup redistributed the braking load optimally from front to rear. Stopping distances remained stable after seven stops, within a foot or two either side of 215*F.

Needless to say, I was impressed. Stoptech showed not merely one-time results but real, measurable improvements in performance where the limits of the stock setup had been exceeded. I followed up the official runs with the ultimate torture test. By that time, our full test schedule had pushed us into darkness, and we noticed the rotors glowing. Sez the magazine guy, "Hey, I have a cool idea for a photo. What if you get them really hot and then stay stopped with the parking brake on so we can do a long exposure?" Surprisingly, Stoptech was more than willing to go along with this bad idea and had its driver get them as hot as possible. He did repeated stops from over 100 mph so we could shoot the glowing rotor. Eventually, the rear pads began to catch on fire while the car sat still. The hard acceleration required to get up to speed even began to cause the Jetta's automatic transmission to falter.

Surprisingly, after Stoptech's tech staff took the Jetta's brakes apart for a "debriefing" inspection, they announced that all was well with both their brakes and the stock rears. Needless to say, I wanted to know more about Stoptech after this demonstration.

I paid Stoptech a visit and learned more than I thought I wanted to know about what it does. Stoptech's overall strategy is to provide a superb product at a price generally below the competition. Solid engineering is at the core of Stoptech's methods. Its goal is to maximize the efficiency of a car's braking system so that all the parts work together optimally. One of the primary focuses is on cooling, but to think only about that misses many of the concepts embodied in a Stoptech system. Quality of the product, and the experience of the user, are paramount. Efficient manufacturing techniques keep prices down, and from opening the box to the maintenance through an open-ended product lifetime, user-friendliness is built in.

The basic difference in function between a two-piece rotor and a typical O.E. one-piece rotor comes down to where the heat goes. The interface between a rotor and hat inhibits conduction of heat into the hub and bearings, while greater airflow increases the role of convection in a two-piece design. The total cooling is much better. Stoptech has done a great deal of research improving airflow and calls its rotor the AeroRotor(TM). Stoptech examined theoretical studies done by GM, Toyota and the University of Illinois, as well as conventional practice by OEMs and the solutions developed by other performance brake companies such as Brembo, Alcon and AP. Computational fluid dynamics (CFD) simulations were done to develop new theory and compare it to other designs. Both existing products and new ideas, created with rapid prototyping techniques, were tested on a rotating flow bench before any metal was cast or cut. As a result, Stoptech reports the AeroRotor has airflow up to 61-percent better than some OEM rotors and 10- to 15-percent better than other racing rotors, resulting in temperatures typically 15-percent cooler than stock and 7-percent cooler than other racing designs.

The aerodynamic features are quite clever. Most significant is a unique vane shape, designed to draw air into the rotor and accelerate it outward. Detail design removes as many restrictions to that flow as possible. The corner of the inside surface of the disc is rounded to help air turn the corner into the vanes, while the disc attachment technique has several helpful features. The spring-loaded shoulder bolts use a much smaller, and thus less obstructive, spring mechanism to reduce turbulence in the critical area just in front of the vanes. Air gaps between the rotor and the hat increase flow through the approach path leading to the rotor, thereby smoothing the flow overall. The other significant part of the system is the caliper. Stoptech's ST-40 four-piston caliper weighs 8.2 lb without pads. One of its most striking features is a bolt-in bridge with a vent for air to escape the edge of the rotor as it passes. With a solid caliper bridge, airflow through the rotor vanes stops as it passes the caliper. By providing a way for the air to escape, Stoptech has reduced the effect significantly. The ST-40 can work with either 28mm- or 32mm-thick rotors, in diameters from 328mm up to 455mm. Piston bores can be anywhere from 28mm to 44mm. Unlike simply putting massive brakes from some supercar on a car that was never designed for them, Stoptech designs its kits to have the proper clamping force on the rotor to work optimally with the rest of the system on any given application.

For smaller rotors, from 313mm to 332mm, there is the ST-20, a two-piston sliding caliper made to fit under smaller, tighter wheels. It can use pistons up to 48mm. In order to get the required stiffness across the bridge, so that the caliper doesn't waver under brake torque, there is no vent for cooling. As well, the pad retention system would block airflow if there was a hole for lightness. The ST-20 is not the maximum performance option; rather it allows the many other benefits of a Stoptech brake system to be applied in situations where the ST-40 is simply too big to fit. Plans are in the works for a four-piston caliper much smaller than the ST-40 for smaller, lightweight cars where the weight of a 12- to 13-in. rotor and corresponding caliper is a greater detriment than the braking benefit.

Stoptech has its caliper bodies high-pressure cast of aluminum, using permanent molds. The castings approximate the final shape very closely, minimizing machining costs and extra weight caused the by presence of unnecessary material. They are machined to final specs in-house, using the latest CNC equipment for maximum efficiency and accuracy. Every two times the door opens on one of its machines, a finished part comes out. Stoptech then ships the machined parts out to specialists for final finishing, which consists of deburring, anodizing and painting. Unlike some competitors, Stoptech calipers are painted before assembly, so the hardware, such as the bolts and crossover tube, are not painted, giving a look Stoptech prefers. Also unlike some competitors, dust seals are used on all Stoptech calipers' pistons, ensuring long service on street or track.

Perhaps the most user-friendly feature of Stoptech's calipers is the fact that they use a standard Porsche-style pad, available in a wide variety of compounds from nearly every performance-brake-pad manufacturer. This saves Stoptech the trouble of becoming a brake pad manufacturer itself, not to mention being the only source of pads for every kit it sells, while giving customers the ability to tailor their friction material to their own needs and budget, a definite added value. As well, there are features built into the caliper to enable the use of a standard Porsche-style brake wear sensor. Compatibility with O.E. safety features is valued.

A feature that matters little once a brake kit is on the car, but is of great assistance to dealers, is Stoptech's packaging. The brake kit is packed in a big box, with smaller boxes inside. Each of the smaller boxes opens kind of like a pizza box; inside is the caliper or rotor wrapped tightly under plastic. However, by unfolding the insert the part is released with no damage to the packaging or part. This means any number of customers can hold the part in their hands and examine it closely without reducing the packaging's ability to present the product in as-new condition. The various components are labeled for which side of the car they go on, so the parts can be unpacked appropriately and installed without stopping to figure out if it's going together backward. In addition, the installation instructions are superb, among the best I have seen for any aftermarket product.

To conclude, Stoptech has shown that its products work, resulting in a top-shelf experience, from opening the box through installation and long-term service. In addition, they are made to the highest standards right here in the U.S. Stoptech is not an enormous company, and hasn't been around forever, so it doesn't have applications for every car. However, if your car is on the list and you are convinced you need more brakes than pads, lines and fluid can provide, it would be hard to go wrong with a Stoptech big brake upgrade.

Author's notes: Look for a feature on the Boston Acoustics Jetta 1.8T and its non-driving entertainment features soon in ec sister magazine, Auto Sound & Security.

For extensive technical information on brake systems in general, see Stoptech's website: www.stoptech.com.