Testing Brakes with StopTech
by Dave Zeckhausen
Brake System Philosophy
Track Testing the Nissan 350Z
Test Area Set-Up
Nissan 350Z Track Model
Performance Model Brakes
StopTech 332mm Front Big Brake Kit
StopTech 355mm Front Big Brake Kit
StopTech 4-Wheel Big Brake
Test Data Summary
As part of their
development process, StopTech fine tunes each brake kit design by taking it
to the track and, if necessary, adjusting that design before it goes to
market. I was invited to participate in a full day of track testing
with StopTech in December, 2002. This article is my "diary" of that
day. After a day of track testing
and 3 days at the production facility in Torrance, California, I have a much better understanding and appreciation
for the engineering and testing that goes into making StopTech big brake kits
work so well.
StopTech's Balanced Brake System Philosophy
StopTech places tremendous emphasis on the concept of a balanced brake
system. While they have several patents related to rotor cooling and
caliper stiffness, what sets StopTech apart from other big brake companies is
their dedication to preserving the factory balance. As the chart below indicates, a
brake kit with too much rear bias not only results in longer stopping distances,
but is unstable without the assistance of electronic stabilization control or
ABS. I can relate to this with my road race car which has an adjustable
proportioning valve. The handling gets pretty scary when I've got too much
hydraulic pressure going to the rear brakes.
Stopping distance vs. front/rear brake bias (Audi S4 data)
If the brakes are too front biased, the front
tires tend to
saturate prematurely and the stopping distances become longer, both with and
without ABS. ABS does not fix improper bias. StopTech controls the bias of their kits by retaining the
stock master cylinder and juggling caliper piston and rotor sizes to
come up with optimum brake torque balance.
An Audi S4 kit was used to
generate the numbers for the chart above. StopTech makes 3 different
kits for the S4, all of which are better balanced than even the factory
brakes. According to the chart, an Audi S4 kit using F50 calipers and 355mm
diameter rotors would be front biased, due to the larger piston sizes used in that caliper. The same
calipers with smaller 332mm
rotors produces the counterintuitive result of shorter
stopping distances than the kit with bigger rotors! A Porsche "Big Red"
conversion that uses adapter brackets to attach Porsche 993TT front and rear calipers
and rotors to the Audi S4 is rear biased and, not only has a longer stopping
distance, but might even be unstable
if ABS is disabled.
By careful selection of caliper piston sizes and exhaustive track testing (as you'll
see below), StopTech has the potential to yield the shortest
stopping distances of any aftermarket brake kit, combined with safe and stable handling.
the Nissan 350Z
I flew out
to California from New Jersey late Tuesday night, December 10th, arriving around midnight. I
was picked up at my hotel the next day at 6:30 AM by Ilja Burkoff, the StopTech test
driver, and we drove for over an hour to a former military airstrip in Camarillo
that StopTech had rented for the day. Two Nissan 350Z sports
cars, a silver Performance model and a copper Track model were waiting for us.
A third car would arrive late in the afternoon for the 355mm front and 4-wheel brake kit
The Nissan 350Z test cars
Test Area Set-Up
The first order of business was to set up the test area.
Matt Weiss, StopTech's Customer Service Manager, spent nearly an hour with a gas powered leaf blower, cleaning off the
braking zone. Other folks laid out cones to mark the braking zones and skid pad
area. A radar gun was set up on a tripod and a cover fitted to prevent
aircraft radar reflections from interfering with our test data. The radar was
interfaced to a laptop running custom software that calculated and plotted
stopping distances and produced tables with all sorts
Steve Ruiz setting up the radar gun and laptop
The support van was filled with tools,
brake rotors, and calipers. There were three different kits to be tested
this day, including a 332mm front, 355mm front, and a 4-wheel kit. In
addition, we needed to test the stock brakes on the Performance and the Track
models in order to have a baseline for comparison. All the tests
(except the 4-wheel brake upgrade) were to be conducted using the same tire
make and model in the same size and on the same size wheels. We had a long
day ahead of us!
The van loaded with tools and brakes
StopTech's Co-Founder and Engineering Manager, suspected the factory Brembo
brakes had never been properly broken in, so he used that as an opportunity
to spend some quality time with me (zooming to 100 mph, then standing on the
brakes - over and over again) while casually explaining all the tests we
would be running and how the data would be collected. Frankly, I think he
was just trying to see how many g's I could take before throwing up.
Fortunately, I don't get motion
sick, but I now have a better appreciation for what my customers go through
when I take them along to bed in their new brakes.
Steve was correct about the factory brakes not being bedded in. They
went into green fade and then, after cooling off, felt much stronger than
when we first tried them out. Now we could run a fair
350Z Track Model with Brembo brakes
Nissan 350Z Track Model Brakes
Our first goal was to fully characterize the factory brakes. So we
started our testing with the Nissan 350Z "track model." Ilja would
drive to the end of the runway and then turn around and head straight
for the radar station at about 64 mph. When he reached the last of three
cones, he would apply the brakes fully, allowing ABS to activate. The
laptop started collecting data before the stop was initiated and
kept on collecting data after the car was stopped. Steve used the
mouse to "lasso" the data on the graph from 60mph to 0mph and discard the
rest. This left us
with a plotted graph that showed how the car performed during the 60mph
to 0 portion of the stop. It's pretty much a straight line. This technique is more accurate than relying on the driver to try to go exactly 60 mph and
then stomp the brakes. It also eliminates the differences between runs
where the driver may hit the brakes more quickly on one run than
another. Many magazines test brakes this way, although some use the
less accurate and less repeatable method of relying on the driver to
gauge when he's going 60 mph. It's important, when comparing tests, to
know how the data was collected.
We ran the car through ten back-to-back stops
from 60 mph. Each time the car stopped, we measured and the
rotor temperatures and then sent the car around for another pass.
After five or six passes, the rotor temperatures stabilized. The
front rotors reached 565
°F and the rear rotors reached 370 °F. We did a total of 10 stops from
60mph and the temperatures varied by about +/- 10 °F, but it was clear that
we could keep this up all day and they wouldn't get any hotter. The
average stopping distance was 117.3 feet.
Measuring rotor temperatures after an 80 mph stop
Next, we ran through six stops from 80 mph, collecting the same
data. The front rotors stabilized at 590
°F and the rear at
400 °F. Average stopping distance was 208.7 feet.
finally, we did four stops from 100 mph. It was somewhat disconcerting to
see the car heading straight for us at that speed, but there wasn't a hint of fade
from the Brembo brakes on the 350Z Track model. The final rotor temperatures
were 721 °F in
front and 477 °F in the rear and the stopping distances averaged 328.3 feet.
Stopping the 350Z
Track Model from 100 mph
The next phase of the test
is to determine how the brakes interact
with ABS and the stability control system. We ran a "Modified J-Turn" test, which is used by engineers who design ABS systems. A skid pad is
laid out with cones and very carefully measured calibration points are marked
with dots of paint. Then, the car is driven around the skid pad to find
the maximum speed it can navigate the constant radius turn. The 350Z
managed to reach 46.5 mph.
Locking up the brakes in the Modified J-Turn Test
Next, the driver makes a run at the skid pad
at 46.5mph. Partway through the turn, he locks up the brakes and the car
comes to a stop. A tape measure is then laid out between the calibrated dots
nearest where the car stopped. Then, a measurement is taken from each wheel
to that tape with the measurement taken along the line of sight from the
wheel to a calibrated reference point. The distance from wheel to tape is
recorded, as is the distances from the dots, and this is all entered into a
laptop. Car wheelbase and track is also entered. The laptop does some
crunching of numbers and comes up with the "departure angle" of the car from
the intended direction. If it is outside of a narrow range, the brake system
needs to be rebalanced with either larger or smaller pistons in the front or
Preparing to measure points for Departure Angle calculation
Of course, the factory Brembo system on the 350Z Track model passed the
J-Turn test, as was expected. The results did show the brakes to be
somewhat front biased.
The final test for the Track
Model was to disable the ABS system and conduct a high speed stop to see if
the front or rear brakes locked up prematurely. This test was
completed without incident and confirmed the front bias detected by the
Nissan 350Z Performance Model Brakes
Now it was time to test the 350Z
Performance Model, which
comes from Nissan with single-piston, floating calipers
and much smaller rotors. We were all very interested to see how the two
factory cars would compare. After ten stops from 60mph, the front
rotor temperature stabilized at around 700
higher than the track model. The rear rotor temperatures reached 478
°F, which was 108 degrees higher than the Track model. The average stopping distance was
118.0 feet, which was less than one foot longer than the Track model.
Very interesting. We figured the difference would become more significant
at higher speeds, so we pressed on.
Stopping the 350Z Performance Model from 80 mph
After six stops from 80mph, and
then four stops from 100 mph, the front rotors reached 804
°F and the stopping distances began to increase as fade set in. I
began to wonder which way to dive if the car couldn't stop, but figured the
test driver would expect us to stay still and would swerve around us.
I kicked myself for not asking about this before we started!
Stopping distances from 80mph and 100mph averaged 210.5 and 333.6 feet
respectively. That's within 5 feet at 100 mph and within 2 feet from
80 mph of the 350Z Track Model's performance. The Brembo brakes didn't
seem to make a significant difference on stopping performance until the cars
started doing repeated 100mph stops, at which point the increased thermal
capacity of the bigger rotors kept brake fade at bay, while the Performance model
with smaller brakes began to experience fade.
The J-Turn test and the
ABS-disabled test went without incident.
The fraternal twins cooling down after the initial brake tests
Now the real work was about to
begin. It was time to test the StopTech 332mm and 355mm front brake
kits But first the cars needed to cool down a bit.
Preparing for the brake installations
the cars cooled, we pulled out the ramps, tools, and brake kits to
prepare for some field installations. I took this opportunity to wolf
down some spicy chicken drumsticks that Ilja had in his cooler. My
jet-lagged stomach was telling me it was time for lunch, even though it was
still mid morning.
The pit crew goes to work on the 350Z Track model
Since the silver car was still too hot to work on, we decided to take a
closer look at the Brembo brakes on the 350Z Track model.
A close-up of the Track model's factory Brembo set-up
We pulled the wheels off and took some measurements. The 350Z Track
model comes with 324mm x 30mm front rotors and 322mm x 22mm rear rotors. So, despite the hype, the rotors on that car aren't as
massive as I had expected. Even the smaller of the two StopTech front
brake kits we were about to test was significantly larger at 332mm x 32mm.
Even more shocking is the price of replacement
Nissan rotors for the 350Z track model. Front rotors (p/n
40206-CD000) are $519 each and rear rotors (p/n 43206-CD000) are $494 each
from the local Nissan parts counter. Ouch! In comparison, the non-Track
Nissan 350Z rotors are $111 each for both front and rear.
Now it's the Silver 350Z Performance model's turn. Stock brakes shown
StopTech 332mm Front Big Brake Kit
After we put the 350Z Track model back together, it was time to install the
first brake kit on the silver 350Z Performance model. I rolled up my
sleeves to help and did most of the installation on one side while someone
else worked on the other.
While removing parts, I
measured the rotors. The front rotor was only 296mm x 24mm and the
rear was 292mm x 16mm. That is a skinny rear rotor! I don't
think the Performance model will stand up to any serious track use unless
the brakes are upgraded.
Mat Weiss finishes the installation while I munch on chicken drumsticks
After the StopTech 332mm front kit was installed and the brakes bled, Ilja
took it out to the end of the runway and did a series of stops to bed in the
new pads and rotors. After it was broken in, he cruised back and forth
to let the brakes cool down. Then it was time to start with the
measured brake testing again.
Measuring Rotor Temperature after 100mph Stop
As before, we did twenty stops, the first ten from 60mph, followed by six
stops from 80mph and then four stops from 100mph. The difference was
noticeable even at 60mph. The stops were several feet shorter than the
stock brakes and the rotor temperature was 155 degrees cooler after just 10
stops. From 100mph, the car stopped 4.3 feet sooner.
Next, it was time to go back to the skid pad for the modified J-turn test.
The results of that test showed the car to be within acceptable limits.
The ABS-disabled test was also successful, so the kit was deemed to be
market ready. Sometimes the results of the J-Turn test will mean they have to go back to the van and install a different set of calipers with
slightly larger or smaller pistons. Thankfully this one was good to go
on the first try. Even so, it took several hours to test.
StopTech 355mm Front Big Brake Kit
Now it was time to test the StopTech
355mm kit. The third test car had arrived with the StopTech
355mm front brakes already installed. This car also had Toyo Proxes
tires and a modified suspension, so a direct comparison to the other cars is
not really possible. We ran through the full set of 20
stops again and found the massive front rotors to be 268 degrees cooler than
the stock rotors after the first ten stops from 60mph and the stopping
distances were slightly better than the smaller StopTech kit.
The slight improvement was probably due to the tires, since the balance was
engineered to be the same as the smaller kit. The J-Turn tests and ABS tests were again aced on the first try.
That was two kits down and one more to go.
Cutting away the backing plate to make room for the 355mm x 32mm rear
4-Wheel Big Brake Kit Kit
The final brake kit to be tested was the 4-wheel
big brake kit with 355mm rotors at all four corners. Given the
undersized stock rear rotors on the 350Z, this is the kit that will need to
be used by anyone who plans to seriously race this car.
Up on the jacks went the third test car again. The rear brakes were installed and the front calipers switched
to ones with bigger caliper pistons. The tiny 292mm x 16mm stock rotors were replaced with much larger
StopTech 355mm x 32mm rotors, requiring that the old backing plates be cut
away to make room. Tin snips made short work of the backing plate
trimming and the rear kit was installed. Next, the front calipers were
replaced with ones that were sized to work with the StopTech rear kit
They utilized larger caliper pistons. We had several sets to try and
the plan had been to run through them in sequence to zero in on the optimum
pair. But we were out of time, so the decision was made to gamble on
the caliper with the smallest pistons in order to shift more braking to the
Smoke rising from the front brakes (hard to see in photo)
By the time we finished
installing the rear brakes, it was getting dark. We would have to
conduct the braking tests with flashlights. We maneuvered all the
vehicles so they illuminated the braking zone and the radar gun and made the
first run from 60mph.
That first run was the best one
that had been made all day. I don't have the data from that run, but I
recall it was around 111 feet from 60mph. We thought we had another
winner. Then things started to go downhill quickly.
Smoke rising from the rear brakes
as the rotor temperature is measured
we made a few more runs, the stopping distances increased as did the rear
rotor temperatures. It was obvious that we had picked the wrong set of
calipers for the front. Unfortunately, we were out of time, so we
aborted the braking runs and moved over to the skid pad to conduct the
J-Turn test. That test confirmed that we were too rear biased, as did
the ABS test. Out of time and out of daylight, we decided to pack it
in at 8:00 PM and continue the 4-wheel kit testing another day. We
were exhausted after such a grueling day, but there was still work to do,
picking up cones, putting away tools, and cleaning up the test area.
We stopped for dinner on the way back to the hotel and had a chance to talk
about the day's testing. A tremendous amount of data had been
collected and we hadn't really had a chance to absorb and process it all.
I was starting to gain a deeper appreciation for the amount of work required
to prepare a StopTech brake kit for market.
The following week, StopTech went back
(without me) to the track and ran the full set of tests on the 350Z 4-wheel
kit again, this time starting with stock bias and working their way down to
the optimum piston sizing required to minimize stopping distances, yet not
mess up the stability control system. Since then, the 4-wheel 350Z kit
has become one of StopTech's more successful kits. The March 2004
issue of "Sport Compact Car Magazine" recorded the best stopping distance
ever for a 350Z running the StopTech 4-wheel kit. That 350Z
required only 98 feet to go from 60 to zero mph!
Summary of Test Data
|296mm x 24mm
||324mm x 30mm
||332mm x 32mm
||355mm x 32mm
||355mm x 32mm
|292mm x 16mm
||322mm x 22mm
||355mm x 32mm