by Christopher Wood
60-0 in 136 feet! Meaningless!
While browsing through a few old car magazines this morning, I was reminded of an old gripe I have with nearly every automotive publication out there. The effectiveness of brake upgrades (and brakes in general) is almost always misrepresented in testing -- everyone seems to quote 60-0 and 100-0 stopping distances or times, despite the fact that brake upgrades are virtually incapable of improving those statistics.
Fact: The tires are the limiting factor in single-stop deceleration performance
Almost any vehicle is equipped from the factory with brakes powerful enough to stop the car at the threshold of wheel lockup from 60 or even 100 mph. What this means is that a car with factory brakes will perform as well in single-stop tests as the same car with a $6000 brake upgrade. So what determines braking performance? The single most important factor in single-stop braking performance is the tires -- magazine braking tests are mostly measuring the tires and the surface they're rolling on.
So why do people spend thousands of dollars on high-performance brakes?
The function of performance brakes is actually heat management, and it takes pretty aggressive driving to expose the weaknesses of factory equipment in most cars -- much more aggressive than a single stop from sane speeds will reveal. Well-engineered brake upgrades are necessary to dissipate the heat generated in repeated stops. Large, wide rotors have an advantage in thermal mass and heat transfer from airflow through the central radial vent. Pad compound upgrades to otherwise stock brakes are effective at allowing the car to stop repeatedly in aggressive driving for two very good reasons:
1. A single aggressive stop from very high speeds is less likely to run the pad surface up to a temperature where its coefficient of friction drops.
2. Operating at higher temperatures dramatically increases the efficiency of radiant and convective heat transfer; the rate at which energy is dissipated skyrockets.
Why do some cars have a reputation for great stopping, even with modest tires?
Static and dynamic weight distribution are a very large factor (secondary to tires) in stopping performance. Because a tire's coefficient of friction decreases as it is loaded, it is most efficient to avoid excessive weight transfer. Porsche "Hand of God" brakes have little to do with the actual stopping parts themselves and more to do with having a very low, rearward-biased center of mass. When I hear a writer gush about an MR2 with stock brakes out-stopping a field of cars with expensive upgrades, leading the reader to believe that brakes are better left untouched, I can only wonder why they insist on wasting time and magazine space on "brake testing".
Next time you're reading your automotive publication of choice, especially one featuring upgraded vehicles, and the writer runs on about stopping distances and "big binders" (or whatever their cute phrase of the month is) you'll know to roll your eyes dismissively and ignore statistics for statistics' sake.
60-0 in 136 feet! Meaningless!
While browsing through a few old car magazines this morning, I was reminded of an old gripe I have with nearly every automotive publication out there. The effectiveness of brake upgrades (and brakes in general) is almost always misrepresented in testing -- everyone seems to quote 60-0 and 100-0 stopping distances or times, despite the fact that brake upgrades are virtually incapable of improving those statistics.
Fact: The tires are the limiting factor in single-stop deceleration performance
Almost any vehicle is equipped from the factory with brakes powerful enough to stop the car at the threshold of wheel lockup from 60 or even 100 mph. What this means is that a car with factory brakes will perform as well in single-stop tests as the same car with a $6000 brake upgrade. So what determines braking performance? The single most important factor in single-stop braking performance is the tires -- magazine braking tests are mostly measuring the tires and the surface they're rolling on.
So why do people spend thousands of dollars on high-performance brakes?
The function of performance brakes is actually heat management, and it takes pretty aggressive driving to expose the weaknesses of factory equipment in most cars -- much more aggressive than a single stop from sane speeds will reveal. Well-engineered brake upgrades are necessary to dissipate the heat generated in repeated stops. Large, wide rotors have an advantage in thermal mass and heat transfer from airflow through the central radial vent. Pad compound upgrades to otherwise stock brakes are effective at allowing the car to stop repeatedly in aggressive driving for two very good reasons:
1. A single aggressive stop from very high speeds is less likely to run the pad surface up to a temperature where its coefficient of friction drops.
2. Operating at higher temperatures dramatically increases the efficiency of radiant and convective heat transfer; the rate at which energy is dissipated skyrockets.
Why do some cars have a reputation for great stopping, even with modest tires?
Static and dynamic weight distribution are a very large factor (secondary to tires) in stopping performance. Because a tire's coefficient of friction decreases as it is loaded, it is most efficient to avoid excessive weight transfer. Porsche "Hand of God" brakes have little to do with the actual stopping parts themselves and more to do with having a very low, rearward-biased center of mass. When I hear a writer gush about an MR2 with stock brakes out-stopping a field of cars with expensive upgrades, leading the reader to believe that brakes are better left untouched, I can only wonder why they insist on wasting time and magazine space on "brake testing".
Next time you're reading your automotive publication of choice, especially one featuring upgraded vehicles, and the writer runs on about stopping distances and "big binders" (or whatever their cute phrase of the month is) you'll know to roll your eyes dismissively and ignore statistics for statistics' sake.
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