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> past driving behavior that may have affected the brake system Could this mean that such a vehicle under test would brake differently than the average driver.

> past driving behavior that may have affected the brake system Could this mean that such a vehicle under test would brake differently than the average driver. Since the brake is constantly being slammed during repeated tests, the software adjusts breaking parameters? Still find it odd to implement such a system, but could explain the inconsistent results.

londons_explore 8y ago
Since they did more tests the following day and didn't see improved performance, it doesn't seem likely related to thermal limiting in software. If I were to guess, it would be that in a sudden stop, something inside the brake mechanism heats up so much it bends or deforms, and then doesn't work so well after that. If my guess is correct, it could be an expensive recall...
- cc439 8y ago
  I can almost guarantee the brake pads glazed over due to overheating. The pad's surface will begin to work harden once a certain temperature threshold is exceeded and that hardened surface has a much lower coefficient of friction than the original unhardened pad. This work hardened material will never return to normal so full braking performance will not be restored until it is ground away by further use of the brakes (light use, you don't overheat them again and make the problem worse). That explains why the poor braking performance was unaffected by an overnight cooldown. All that said, if the Model 3 is glazing brake pads with a single emergency stop then they need to issue a recall and figure out a fix.
  - sliken 8y ago
    The whole brake from 60-0 10 times quickly seems like a stupid metric. Would you rather have shorter stop times, but a design that fails at 15 times? Or a brake that adapts to that load and progressively stops more gently. Any sane driver would adjust. Seems pretty stupid to evaluate cars on such a weird metric. Sure 60 to 0 or 80 to zero, but what sane person is going to accelerate up to speed as quickly as possible and try again. Maybe Tesla's doing so poorly because it gets back to 60 quicker than it's competition.
    - pwinnski 8y ago
      Tesla's newest car doing badly at a test does not invalidate the test, which has been standard for many years. The ability to stop quickly at highway speeds is, in fact, something worth testing, and 60-0 stopping time is a great thing to test.
    - cjhopman 8y ago
      > The whole brake from 60-0 10 times quickly seems like a stupid metric > Sure 60 to 0 or 80 to zero, but what sane person is going to accelerate up to speed as quickly as possible and try again. Isn't that an argument for CR's test? They explicitly drive 1hr between each braking test so that it's not just "accelerate up to speed as quickly as possible and try again".
      - sliken 8y ago
        I dug for information like that. I only found "Our automotive engineers conduct a series of brake tests from 60 mph to a standstill on wet and dry pavement to measure stopping distances." Do you have a reference for the 1 hour between brake tests? My reference is: https://www.consumerreports.org/cars-how-consumer-reports-tests-cars/ https://www.consumerreports.org/cars-how-consumer-reports-te...
        deleted 8y ago
        [deleted]
        cjhopman 8y ago
        Ah, it's not 1 hour, it's 1 mile. It's in the article. Still clearly not "accelerate up to speed as quickly as possible and try again". "As its name implies, CR’s braking test is meant to determine how a vehicle performs in an emergency situation. The test is based on an industry-standard procedure designed by SAE International, a global engineering association. Our testers get a car up to 60 mph, then slam on the brakes until the car comes to a stop. They repeat this multiple times to ensure consistent results. Between each test, the vehicle is driven approximately a mile to cool the brakes and make sure they don’t overheat."
RaceWon 8y ago
The folks who test cars at CR are Expert drivers, I was impressed by some YT footage I have seen; if they are saying the brakes are inconsistent then that has nothing to do with the brakes being cooked by hot lapping. Rather it means that lifting off the throttle at the same speed and applying the brakes with the same force, and at the same place on back to back runs will yeild different results. As a racer I can tell you that makes the car Dangerous and no fun at all to drive; if can't trust the car to do the same thing time after time--it's worthless from a pure driving perspective.

londons_explore 8y ago

Since they did more tests the following day and didn't see improved performance, it doesn't seem likely related to thermal limiting in software. If I were to guess, it would be that in a sudden stop, something inside the brake mechanism heats up so much it bends or deforms, and then doesn't work so well after that. If my guess is correct, it could be an expensive recall...

cc439 8y ago
I can almost guarantee the brake pads glazed over due to overheating. The pad's surface will begin to work harden once a certain temperature threshold is exceeded and that hardened surface has a much lower coefficient of friction than the original unhardened pad. This work hardened material will never return to normal so full braking performance will not be restored until it is ground away by further use of the brakes (light use, you don't overheat them again and make the problem worse). That explains why the poor braking performance was unaffected by an overnight cooldown. All that said, if the Model 3 is glazing brake pads with a single emergency stop then they need to issue a recall and figure out a fix.
- sliken 8y ago
  The whole brake from 60-0 10 times quickly seems like a stupid metric. Would you rather have shorter stop times, but a design that fails at 15 times? Or a brake that adapts to that load and progressively stops more gently. Any sane driver would adjust. Seems pretty stupid to evaluate cars on such a weird metric. Sure 60 to 0 or 80 to zero, but what sane person is going to accelerate up to speed as quickly as possible and try again. Maybe Tesla's doing so poorly because it gets back to 60 quicker than it's competition.
  - pwinnski 8y ago
    Tesla's newest car doing badly at a test does not invalidate the test, which has been standard for many years. The ability to stop quickly at highway speeds is, in fact, something worth testing, and 60-0 stopping time is a great thing to test.
  - cjhopman 8y ago
    > The whole brake from 60-0 10 times quickly seems like a stupid metric > Sure 60 to 0 or 80 to zero, but what sane person is going to accelerate up to speed as quickly as possible and try again. Isn't that an argument for CR's test? They explicitly drive 1hr between each braking test so that it's not just "accelerate up to speed as quickly as possible and try again".
    - sliken 8y ago
      I dug for information like that. I only found "Our automotive engineers conduct a series of brake tests from 60 mph to a standstill on wet and dry pavement to measure stopping distances." Do you have a reference for the 1 hour between brake tests? My reference is: https://www.consumerreports.org/cars-how-consumer-reports-tests-cars/ https://www.consumerreports.org/cars-how-consumer-reports-te...
      - deleted 8y ago
        [deleted]
      - cjhopman 8y ago
        Ah, it's not 1 hour, it's 1 mile. It's in the article. Still clearly not "accelerate up to speed as quickly as possible and try again". "As its name implies, CR’s braking test is meant to determine how a vehicle performs in an emergency situation. The test is based on an industry-standard procedure designed by SAE International, a global engineering association. Our testers get a car up to 60 mph, then slam on the brakes until the car comes to a stop. They repeat this multiple times to ensure consistent results. Between each test, the vehicle is driven approximately a mile to cool the brakes and make sure they don’t overheat."

RaceWon 8y ago

The folks who test cars at CR are Expert drivers, I was impressed by some YT footage I have seen; if they are saying the brakes are inconsistent then that has nothing to do with the brakes being cooked by hot lapping. Rather it means that lifting off the throttle at the same speed and applying the brakes with the same force, and at the same place on back to back runs will yeild different results. As a racer I can tell you that makes the car Dangerous and no fun at all to drive; if can't trust the car to do the same thing time after time--it's worthless from a pure driving perspective.