Written by Per Schroeder
From the April 2006 issue
Posted in Electronics & Electrical Systems
Our roads are a wasteland of construction zones, lawsuits and lackluster drivers—and that’s just what we encounter on the way to work in the morning. So while the cars of today are safer than ever before, it’s still a concrete jungle out there.
We are big proponents of active safety measures like ABS brakes and cars that can actually swerve around an obstacle rather than flipping over and bursting into a ball of flames. Sure, improvements in seat belt and airbag technology have helped, but we’d suggest that what actually saves more lives on our roads are the active safety devices, rather than the passive ones. We just don’t hear about the countless near-misses and “Oh $#@!” moments that end with a sigh of relief rather than a sob of anguish.
But if you listen to the bench racers in the pits and on the online forums, our friends and readers are Fangio, Nuvolari and Villeneuve all rolled into a Locost-lovin’ package: They are better on the brakes, they dance with finesse on the gas pedal and they use the steering wheel like a surgeon’s scalpel, on the track and off. Many members of the hardcore elite consider ABS brakes a waste of space, and traction control something for their grandmas. And please, don’t let them get started on the geegaws and gyros that make up a stability control system.
While the purist may argue that these active safety measures are creating a breed of dumb drivers, the truth of the matter is that these devices have saved our bacon time and time again. This is not because of our driving, mind you (no, really), but rather because of things that are beyond our control, like that inattentive SUV driver in the oncoming lane. Active safety measures can really work on the street. They can even help Mr. Club Racer avoid that deer in the road or get his Ford F-350 to stop when it’s towing that oversized enclosed trailer.
During the past 20 years, antilock braking system technology has improved to the point where we would suggest that it can help reduce lap times on track as well as being a real benefit to street driving. We’ve seen some well-funded autocrossers retrofit factory-optional ABS systems onto Toyota MR2s to prevent front wheel lockup, while others go out of their way to find that elusive first-generation Miata with both a Torsen differential and the ABS.
Traction and stability control have a place on the race track as well. Formula 1 teams have successfully used traction control to rein in overzealous drivers and keep their mega-money rocketships on the straight and narrow. Many of these systems have been banned, including launch control, which is a good indication that they worked well on the track. While the race systems have different operating parameters (allowing more slip angle than a minivan, for example), it does give some indication that this technology can be used to make our cars faster.
The GRM Project MINI Cooper S that we built for BMW CCA Club Racing was equipped with both stability control and ABS brakes. We kept our ABS functional, but turned off the stability and traction control during races. After an off-course excursion during a pounding rainstorm at Roebling Road, we actually turned the stability control back on to finish our lapping session in one piece. The horror! But let’s do the math: Wet track + cold temperatures + rubber buildup = slicker than owl snot. Did that stability control save our butts? You betcha! Perhaps the time had come to take a closer look at these driver aids.
Our contention is that ABS brakes, traction control and stability control are not necessarily things to be feared. Like anything, they can be misused, which in their case can hurt both the driver and the car, but they are not the evil foes that our bench racing friends say they are. Additionally, the fact that our atmosphere is not always bright and sunny means that rain and inclement conditions can test even the best of drivers—and that’s where we think these features can help.
To test our hypothesis, we picked a safe and consistent test track where we could spin our tires and lock our brakes until the cows came home. We also needed the ability to wet down the track evenly to simulate a steady rain. The Tire Rack’s test facility meets these criteria, and those friendly folks also offered up their brand-new 2006 BMW 325i as our test mule. The Tire Rack’s BMW and their track are used to compare the tires that they sell in a safe and repeatable manner. This makes both of them excellent for our intentions.
The new E90-chassis 3 Series BMW is a quick and confident partner for sporting and daily use. It is, however, packed to the gills with electronic gizmos, like many modern cars. In addition to a sophisticated ABS system, it also has Dynamic Traction Control and Dynamic Stability Control as standard features. The 325i allows the driver to select three different modes for driving. The basic setting is Dynamic Traction Control (DTC) combined with Dynamic Stability Control (DSC) and Antilock Braking System (ABS). You can turn off the DSC so that you just have the Dynamic Traction Control, or you can turn off both the DSC and the DTC so that you’re left with just the ABS brakes. We also went one better and disabled the ABS by pulling its fuses so that we were left with no electronic aids.
We used Goodyear’s Eagle F1 GS-D3 as our test tire on the BMW. We’ve heard great things about this maximum performance three-season tire and decided that it would make an excellent choice for our wet and dry testing. A set of scrubbed-in Y-rated 225/45R17 tires were mounted on 17x8-inch ASA AR1 rims. These rims were used with a 5mm spacer to make the net offset equal to 35mm, which is 1mm away from stock. While the car will handle a 40mm offset wheel just fine, The Tire Rack uses the spacer to keep the scrub radius as close to stock as possible to minimize any variables in testing.
ABS has become entirely commonplace on dealership lots. It’s actually hard to find new cars these days that don’t have ABS as a standard feature. The system prevents the wheels from locking during braking by sensing a differential in wheel speed from wheel to wheel, or an abnormally rapid deceleration. Hall effect sensors are triggered by the turning of a toothed ring that is mounted to the wheel hub. The ABS “brain” monitors the blip of each of these sensors as the toothed ring passes by, and if one sensor starts lagging behind or stops sending an impulse (indicating the wheel had stopped), the braking force to that wheel is reduced to allow the tire to start spinning again. This is done very quickly so that all the driver feels is a mild pulsation in the brake pedal as the car continues to slow down in a safe, straight and controlled manner.
Traction control uses the same sensors and information to determine if the drive wheels are spinning due to excess throttle. If one of the rear wheels is turning too quickly, the ECU tells the electronic throttle to back it off until the wheelspin is eradicated. This is felt as a sudden reduction of power and, in extreme cases, can feel as though the car just fell on its face.
According to BMW, their Dynamic Stability Control recognizes unstable driving conditions such as understeer and oversteer and, in these cases, helps the vehicle maintain a safe course within physical limits by reducing engine output and through braking actions at the individual wheels. We called this the Full Nanny Mode, since the DSC resolutely keeps the shenanigans to a minimum—just like an overzealous baby sitter.
The internal workings of the DSC are quite remarkable. An internal accelerometer feeds information to the car’s ECU and this is supplemented by speed and steering information from other sensors like the ABS/DTC hub sensors, a steering angle sensor and even the feed for the speedometer. This information is compiled and used to keep the car on the road.
If the car senses the yaw of oversteer, the throttle is reduced and brakes are applied to the outside (of the turn) front wheel. If understeer occurs, the inside rear wheel is slowed in addition to the reduction in throttle input.
The BMW owner’s manual carries this caveat with regard to these active safety devices: “The laws of physics cannot be repealed, even with DSC. An appropriate driving style always remains the responsibility of the driver. Therefore do not reduce the additional safety margin by taking risks.” In other words, don’t be a jackass.
Enter the Jackasses
The Tire Rack’s Woody Rogers and GRM’s Per Schroeder were our designated drivers for our test. Woody admits to having well over a thousand laps on the asphalt at The Tire Rack and can vary his braking points by fractions of an inch to snag that fast lap. He is a machine and would represent an experienced driver on a very familiar track.
Per now has maybe 100 or so laps under his belt at this South Bend, Ind., facility, but is still learning the intricacies of this particular bit of asphalt. For the purpose of this test, Per would represent a less experienced driver on an unfamiliar road.
Our initial intention was to do our dry testing during the morning and then wet down the track for the afternoon’s runs. A drizzly October day changed our plans, however, so we wet down the track for our first test and crossed our fingers that sunny skies would grace us on the following day before we had to catch a flight back to Florida. This worked out well, with the exception of having to reduce our number of runs for the second day to conserve time, and we got some pretty interesting data for our efforts.
Wet Conditions—3 Consecutive Laps
This is the mode that The Tire Rack normally uses for tests; as such, it was very familiar to Woody. The car slips and slides, allowing understeer or oversteer of both the lift-throttle and mash-the-gas variety. This mode requires a lot of driver concentration, but also gives the driver immediate feedback on what the tires and car are doing, and rewards driver skill with the quickest lap times. It also allows the driver to use throttle and vehicle dynamics to minimize lap times, if skill allows.
While the car can slip and slide sideways under the driver, it’s very confidence inspiring to know that the car will, in fact, slow down for the next corner. This allows you to chuck the car around and still nail the apex with aplomb.
This mode provided the fastest times of the four modes on average for Woody, but wound up second on average with Per’s runs included. At this point in the test, Per was still on the steep side of the slick track’s learning curve. Woody’s third run wound up being the fastest raw time in the wet.
DTC and ABS
At first, driving with the traction control and ABS both switched on proved to be difficult. After our first stint with just the ABS, we were accustomed to using the throttle to help steer the car around some of the tighter corners if understeer was present. We adjusted our driving style during the three laps and experimented a bit, finding that slower entry speed to prevent understeer while squeezing the throttle instead of hitting it hard minimized the intrusion of the traction control. There is a fine line here; a little control helps optimize acceleration in the wet, but too much “assistance” slows the car. Some more practice and familiarization with the system might have allowed us to be a bit faster with it. Woody notes, “I sense that autocrossing on a course I am not familiar with, this could be a good mode to let the electronics help me optimize, and prevent too much power-on oversteer when surprised by a puddle or slick spot.”
Per found his fastest run in the soggy conditions in this mode, and his quick time helped the DTC-plus-ABS mode garner the fastest average overall with a 33.043. Woody’s times were a click or two slower than with just the ABS. The combined mode made it easier for the learning driver to get around a wet course and thus helped Per more than Woody.
DSC, DTC and ABS
The Full Nanny Mode was certainly the most intrusive and not really that much fun to drive on the track. But driving safely isn’t always about fun, and this mode had the fewest bobbles as we flung the BMW from corner to corner.
For Woody, the Full Nanny was a bit slower than driving in the no assist/no ABS mode, and was seven-tenths of a second slower than his fastest mode. “As soon as the car begins to slip, slide, spin or push the system jumps into action,” he observes. The learning response of the driver is to drive so as to avoid activating the system—safe on the street, but slow on the track.
“It feels like the stability and traction control systems cannot anticipate what is coming next,” Woody observes, “and once the vehicle crosses some threshold the system intrudes dramatically. The driver always has the advantage of knowing what is coming or what he wants to happen next, and can set the car up for the next situation. The electronic aids do not have this ability.”
Per found the Full Nanny Mode to be as fast as his earlier ABS-only runs, although this can be attributed to his steeper learning curve on the slippery course. The average in this mode wound up being our slowest, with a mean of 33.484.
No Assist/No ABS
Once everything was turned off, our drivers found that the vehicle dynamics were the same as with the ABS-only mode, and the car was very easy to drive except for one obvious difference: Without the ABS assistance, the braking was simply atrocious. There was little in the way of feel for impending lockup, especially at the right-front tire as it entered the right turn for the finish.
Woody comments, “The brakes were very hard to modulate. This vehicle appears to have a massive forward bias to the brakes, as without the ABS to balance things, the front tires locked up very easily. This made corner entry challenging, and required that I apply gentle pedal pressure very early—earlier than I thought was necessary with the grip level and tire capability.”
This mode was nearly as slow as the Full Nanny round in the wet, with an average of 33.369; Woody’s fast time was a 32.861. Much of the extra course time was simply due to slowing down extra early for turns.
Dry Conditions—2 Consecutive Laps
In the dry, the ABS-only mode quickly established itself as the way to go for fast lap times. Woody and Per ripped off some clean and consistent runs with the ABS-assisted brake pedal chattering away on corner entry.
As it was in the wet, this mode was familiar and quick for Woody. “I can feel what is going on with the tire and the vehicle,” he reported, “which allows me to optimize performance and correct minor driving mistakes mid-corner. Some inside wheel spin is evident powering around the first turn and through the slalom. Around the fast sweeper the car seems to be very neutral, which is good for corner exit speeds.”
The average times were the fastest in this mode—just 30.038 seconds—and it was the clear winner in driver feedback. Per found his fastest dry times with this setup, while Woody had his fastest average in this mode as well as his second fastest single time (29.784).
DTC and ABS
Behavioral psychologist B.F. Skinner would be proud: The traction control system clearly rewards a slow in/fast out driving technique. Woody recommends, “Get the car slowed early and power past the apex, squeezing the throttle as you unwind the wheel to prevent too much wheel spin and invoking the full traction control. Learn to work within the system and the grip of the tires results in quick lap times.” The flip side of this is the punishment: “But if you make a mistake and get into the corner a bit too hot,” Woody says, “all you can do is scrub off speed with brakes and understeer, which delays getting back to the power to help turn the car or accelerate to the next corner. If you don’t delay throttle application, the system will do it for you.”
Our conditioning rewarded us with an average lap time of 30.349, just one-tenth behind the no-assist mode and about three-tenths behind our ABS-only session.
DSC, DTC and ABS
The Full Nanny Mode was even less fun to drive in the dry than it had been in the wet; no surprise that this wound up being our drivers’ least favorite session. Both Per and Woody commented on how intrusively the system reacts in typical autocross maneuvers.
Woody explains, “The first level of the system, which uses braking at individual wheel positions to help steer the car, kicks in much earlier than I think is necessary. Maybe there is less grip than I think, but the system doesn’t really like much slip angle.”
The second level of the system, Woody says, is equally noticeable. “Power-on wheelspin that kicks the rear end out quickly results in reduced power output. Once the slide stops, the system hesitates for what feels like an eternity before returning full power.”
Per and Woody both discussed the feeling of simply waiting for the car to get going again. “You can count the tenths of a second click by as the car rolls along at less than full power, or at less than what the driver is asking from the throttle position,” Per says.
Predictably, the DSC, DTC and ABS mode was the slowest of the bunch with an average of 30.923, or about nine-tenths of a second behind the ABS-only mode. This is a much greater difference than we observed in the wet sessions.
No Assist/No ABS
In our dry sessions without the ABS braking assistance, the car behaved nearly the same as it did in the wet. The apparent forward-bias of the brake system made braking anywhere close to the traction threshold very challenging. The rear tires never locked, while the fronts would lock with anything more than a brush of the pedal.
Woody notes, “Driving around the fast sweeper into the braking zone with the lateral load on the car and the camber of the track surface, 30-foot skid marks were almost impossible to avoid without resorting to driving below the limits of the rest of the car.”
Driving at the cornering limit into the sweeper and the tight 90-degree right-hander after the braking zone resulted in a destroyed inside front tire. We were faced with a choice: save the tire with slow speeds, or drive through the turns at the handling limit and punish the inside front tire in the process. According to Woody, “The skid marks from this portion of our test are still on the track now, three months later.”
This mode wound up being Per’s second slowest, while it netted Woody his fastest single run of 29.750. Once their times were averaged, this was the second fastest mode with a fair amount of deviation between runs. Credit the sketchy braking zones that made it too easy to overshoot a corner.
Wrap It Up
Once the dust cleared, the screeching of the tires stopped echoing off nearby buildings, and our mushroom cloud of tire smoke drifted away, we were left with some interesting data. As we had predicted, the electronic driver aids weren’t much of a hindrance to fast lap times, especially in the wet.
ABS was the clear winner in our tests in the dry, and we posted some very respectable lap times in the wet with this system engaged. On the dry track, the ABS-only mode was the most fun to drive and the system helped our lap times be more consistent.
Traction control can be helpful in wet conditions, especially for a driver who is less experienced on a track. If it was raining at an event, we would consider using the traction control to keep the car moving toward the finish line. Keep in mind that the idea here is not to mash the gas and let the computer do the work; a driver’s best bet is to be careful on the gas and if you do get an unexpected bit of wheelspin, the traction control can save an otherwise solid run or lap.
Stability control can be helpful at higher speeds in really slick conditions, but as the speeds decrease and the surface conditions improve, the benefit to lap times goes away. Driver familiarity and expertise on a track also minimizes the benefits of traction control to some extent. On the flip side, an experienced driver can slow down the car enough and work around the system to come up with nearly identical times.
The public roads are not filled with expert drivers, as evidenced by the nation’s plentiful salvage yards, and this is where stability control systems can shine. Even a Formula 1 World Champion can’t predict the future to see that accident waiting around the corner. Stability, traction control and ABS brakes can mean the difference between life and death. We’re just thankful they can also be turned off for performance use.
Interesting article. I would have liked to have seen the effects of DSC separated from DTC though. There have been times when I have felt the DSC system kick in on my car and been thankful for it. I am never happy about the DTC system kicking in though(damm killjoy).
On paper it seems that the DSC system could be helpful to even an experienced driver when it comes to keeping the car pointed in its intended direction.
I don't understand why so many manufactures put the DTC and the DSC system on the same switch...
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