NHTSA Tracking Braking Loss on Prius Hybrids

Discussion in 'Gen 3 Prius Main Forum' started by RobertMBecker, Dec 24, 2009.

  1. john1701a

    john1701a Prius Guru

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    This response has been around since 2003.

    The feel is much improved in the new model.

    When will there be accidents?
    .
     
  2. nooaah

    nooaah New Member

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    I made a post about this when I got my 2008 Gen II over a year ago. I experience this "issue" just about everyday in the same spot going downhill with my Gen II and now my Gen III. In fact, it happens so often that I get a chance to observe my change in speed.

    In my experience with TWO Priuseseses, the gain in speed due to the brake cutting momentarily doesn't even get registered on the speedometer. I'm not excusing Toyota for letting this issue skip across multiple vehicle generations, and there's no doubt they're aware of it if they actually do test drive these cars.
     
  3. rachaelseven

    rachaelseven New Member

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    Just is. The shock factor is hard to describe if it hasn't happened to you. I consider myself a pretty good driver - not many adverse events in my 24 year driving history and I held an SCCA racing license for a bunch of years. I've slid cars sideways at 80mph before and I can assure you that I don't panic easily. But this changeover, cutout, whatever it is, is really quite unsettling. And the sort of road condition that causes this behavior is not even always obviously visible, let alone expected - I've had it happen on perfectly flat drain grates on warm dry days, so it will catch even a very attentive driver quite by surprise. It's like hitting black ice in Florida in July. It happens during gradual braking, in casual maneuvers, often in the last few dozen feet before a gentle stop... hardly the time when a driver is on high alert for adverse conditions. And as has already been correctly pointed out, whether it is an acceleration or a loss of breaking, there are undoubtedly an extra few feet covered during the tenth of a second it takes to realize you need to press the pedal harder, panic or not. And sooner or later, that manhole cover will be in the wrong spot and those extra few feet will end up putting bumper in contact with another bumper... or perhaps a leg. It is a virtual inevitability with the system designed the way it is - brakes can be a lot of things, but they should never be unpredictable in routine conditions.
     
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  4. fuzzy1

    fuzzy1 Senior Member

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    If that someone was going over 2.2 mph when they hit that pothole a tenth of a second before the crosswalk, they were already destined to overrun the crosswalk even under perfect conditions with perfect brakes. Prius is already in pure friction at 7 mph. Stopping from that speed in a tenth of a second implies a 60-0 stopping time of 0.86 second, or a 60-0 stopping distance of under 40 feet. Not possible with rubber tires.

    So far, I can personally judge this only by a couple incidents of brake dropout going over humped railroad tracks, and neither incident was any more disconcerting to me than the first few unexpected pulsating ABS activations in my first ABS-equipped car.

    There have been a number of cases of other drivers so rattled by this ABS 'buzz' that they released the brakes -- defeating the ABS entirely -- and collided with things ahead. How many lawsuits have resulted from this, and how have they been resolved.
     
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  5. Jim Clark

    Jim Clark Member

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    I have not experienced this phenomenon myself. It's the wife's commuter car and I don't drive it much. I'll have to take it out and try to make it happen so I can understand. I'll ask her if she's experienced anything like it but she's pretty clueless when it comes to cars. But, if it had happened to her and "shocked" her, she would have said something.

    I think there are enough concerns that it needs to be carefully examined and tested by Toyota. It may be "normal", BUT, if it increases braking distance by more than a very small amount when it happens, it's a problem.

    It may only be momentary when it happens but at least some people here are concerned about a possible safety issue.
     
  6. john1701a

    john1701a Prius Guru

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    Makes you wonder how drivers react to VSC.

    They could easily counter that when hearing the beep too, defeating the purpose entirely.
    .
     
  7. TheSpoils

    TheSpoils Member

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    Come on folks, most of us have experienced the ABS effect (ABS has been around a long time already), and i don't think people are complaining just for the fun of it. I have the prius and a 2007 altima hybrid (which is basically a larger version of the prius since it is all toyota hybrid components) In the altima, if I am braking and hit a pot hole I can see the regen indicator cut off, but the braking remains constant. In the prius the regen continues after a pot hole but the end result is a lurch/surge/reduced braking effect. I seriously don't want to see any reduction in efficiency caused by some recall which will address the problem, I have merely made myself aware of the handling characteristics and have adjusted my driving habits around them to compensate. And, I know most of you will be upset by this comment, The Prius is not a perfect car, It is extremely fuel efficient, but not perfect by far.
     
  8. Rhino

    Rhino New Member

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    I think the idea is that during commuting, you want to get in line behind the red light as soon as possible as a courtesy to the person behind you. Taking the minimal amount of space in the shortest amount of time. The alternative is that everybody brakes early, then creep forward creating more work for everyone and backing up traffic even more - perhaps backing up traffic beyond one intersection because fewer cars will fit in one block.

    Some people are even worse. They slow to a crawl .25 miles from the red light and crawl to the intersection. Sometimes, they are wrong and the light turns green and they are 20 car lengths from the light and not ready to go ASAP, slowing everyone down.

    I don't do it anymore because I want a margin of safety now.
     
  9. fuzzy1

    fuzzy1 Senior Member

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    'Getting in line as quickly as possible' sounds more like a road rage survival strategy than a courtesy. But I don't live in an aggressive traffic region.

    On my normal routes it won't do jack to speed up traffic flow, because packing everyone in as close as possible means cars have to wait longer to start moving in order to maintain safe following distance. The lights are farther than a single block apart, more like 4+ blocks, and I rarely travel when traffic backs up multiple lights.

    And it has always been a terrible waste of fuel and brake pads.

    As for crawling to stop lights, I see it succeed and speed up the lane much more often than it fails.
     
  10. fjpod

    fjpod Member

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    I've noticed this several times going over bumpy patches while making a turn. It sure is disconcerting, but i don't see much of a safety issue. Actually, it makes you pay more attention to road conditions and the speed at which you take turns. I have to admit my tires are inflated to 40 psi and I'm sure this contributes. I've driven many cars with ABS and have felt some kicked in more easily than others. I still haven't gotten used to the feeling of ABS reducing my braking and would much prefer to control my own. I spent 20 years learning how to do it myself, then they change it on me...damn.
     
  11. Rhino

    Rhino New Member

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    Maybe you and I are referring to different things. I don't mean braking at the last moment like you are going to ram the person in front of you to teach them a lesson. I mean braking at a more reasonable speed with room for error but not optimizing for gas mileage.

    Also, I think you don't live in a city. In places like New York, there are 20 blocks per mile. If each car pack in close, you can fit maybe 15 cars per block. If each car takes it time slowing down, maintaining distance and constant speed, when the light all turn red, you maybe can only fit 7 cars per block. It is more like musical chairs in the city, when the lights turn red, you are stuck on the block you are in.

    The courteous thing to do in NY is to go with the speed of the lights. But if the lights should turn red, to pack it in so more cars can fit behind you in the same block before the light turns red behind you, all the people behind you cannot be in the same block as you.

    In the burbs, with half mile blocks, it is still courteous to move it a bit so that the people behind you can cross before the light turns red on them. Some cars just move fast enough so that they are the last to cross before the light turns red. As for the mileage/carbon footprint argument - I think it is passive aggressive road rage all the same. No mileage is gained by having the guy behind you stop. And if the guy behind you have to gas it to catch up, the combined carbon footprint will be higher. The combined brake pad wear will be higher. So if you are individually green, but causes others to use more gas, in the end, is it better for the environment?

    It must be fun for some people (I'm not referring to you) to leave people behind you in the dust, behind a red light, but I am not the type to enjoy that type of petty advantage. I don't drive at the speed I want, but at a speed that is good for the person or persons behind me too.

    I am referring to braking and driving characteristics in general, this is not referring to you in particular since I don't know how you drive and we live in very different types of traffic.
     
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  12. Darwood

    Darwood Senior Member

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    Ironic that a few posts happen here and only days later, the posts are used as a journalistic reference to criticize the Prius.

    http://www.msnbc.msn.com/id/34611930/ns/business-autos/

    "Chat rooms such as Priuschat.com dedicated to Toyota’s fuel-efficient hybrid are peppered with concerns raised by owners of the third-generation Prius, which was launched for the 2010 model year."

    I think this is a planned attack, using Priuschat to lend credibility.
     
  13. efusco

    efusco Moderator Emeritus
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    Holy cow, what a one sided ill informed piece of garbage.
     
  14. Darwood

    Darwood Senior Member

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    Note at the bottom from that article. (Paul wrote the article)

    "A version of this story initially appeared on TheDetroitBureau.com, an independent Web site co-owned by Paul Eisenstein."
     
  15. bighouse

    bighouse Active Member

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    I read the article and it seemed fair enough to me. I love my Prius and hope the attention to this situation causes Toyota to issue a fix for it. Why would anyone NOT want to see Toyota remedy this brake-loss issue????
     
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  16. bestmapman

    bestmapman 04, 07 ,08, 09, 10, 16, 21 Prime

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    I thought the same thing. I was wondering if the low post count users were up to something. Several new threads started by them were possibly an attempt to stir up credibility for something. And now we have an article.

    Note: I went out yesterday and tried to make the loss of braking happen and I could not. Everytime I sent over a bump or pot hole I tried and not once did it happen to me.
     
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  17. wonmore

    wonmore New Member

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    My 2001 Dodge Dakota has a behavior that seems to be on par with this. If I am breaking and the front wheels jump over a bump or rut in the road, when they come back down, the breaks have released because the tires slowed so dramatically once they were no longer in contact with the ground. It can be very unnerving, but it also is a complex thing to deal with using just sensors.

    I'd think that the ABS could detect no change in braking pressure and the unexpected change in wheel speed, and wait to decide whether ABS needs to activate for a brief moment.

    I also want to start calling my road dept and complaining about these rough intersections and tell them what I'm experiencing.
     
  18. Darwood

    Darwood Senior Member

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    I can make it happen on a particular pothole so I don't doubt the issue. But as pointed out, it's a minor irritant to newer Prius drivers unfamiliar with the car. It is NOT an issue in an emergency breaking situation. Without that behavior, we could not have regenerative breaking and ABS togethor.
     
  19. bighouse

    bighouse Active Member

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    I don't get it. Honestly. Can someone tell me why there are so many people on this forum who just want to say "ignore the situation, it's fine" when it seems so obvious to me that when you have a car that loses its braking ability for even a second or two during critical operating events like stopping at an intersection due to uneven pavement/potholes/cobblestones/traffic grates/whatever it's a potential for someone to get involved in an accident?!?!? I am not trying to bait anyone here, I just don't honestly get it.

    Almost everything falls under a bellcurve in life. Sure, the vast majority of us will have no problem adjusting and compensating for this lock of braking when it happens. I adjust and can handle it fine. But, we're in the center and the end of the bell curve- those in the opposite end won't fare as well in the same situation. Someone will eventually get hurt because BRAKES SHOULD NEVER FAIL! And there are PLENTY of people in the opposite end- newer drivers with less experience behind the wheel, elderly drivers with slower reaction times, etc...

    Some people are dumping on those of us who are complaining about it or saying it's an issue. And, I don't get why those who do so are doing so. Is it because there's such a fanboy mentality here on PriusChat that you can't bring problems to light? I hope not, when I joined up I thought this forum was a fair and honest group of PRIUS owners who love their vehicles and want to learn as much as possible about them, the good and the bad. I'm beginning to think that some here work for Toyota's PR department and don't really care much about holding Toyota's feet to the fire to improve the safety and operation of their vehicles!

    I want Toyota to succeed entirely with their current and future offerings to the automobile enthusiasts out there. I look forward with eager anticipation to see what cars they offer in the future that push the hybrid and high technology forward in the auto industry. I applaud them for making the most FE car in the industry that is not only FE but beautiful and fun to drive- again, I love mine. One way for them to assure their continued/future success is to address the issues their current lineup has by listening to their customers complaints and issues and finding remedies to problems. That can't be more true when it comes to issues of potential safety.

    This thread was not the first on this braking issue. It's been mentioned before by others, myself included. I predicted before that, due to the potential safety issue it will grow in scope- others will pick up the information and run with it so count on hearing about it on your local news channel on television soon. It's unfortunate for Toyota that it follows on the heel of the stuck accelerator/floormat issue. But, every company in the world should be held accountable to its customer base and especially to matters involving the safety of others.
     
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  20. rumpledoll

    rumpledoll Member

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    These are suspicious posrs, I agree. The behavior of my 2010 Prius V is the same as the behavior of my 2007 Prius. Over a series of large irregularities or over a short stretch of slick surface, such as a wet/icy manhole cover, the brakes loose *some* effectiveness. Is it the anti-lock mechanism kicking in? Could be. But even without anti-lock brakes, braking over such surfaces will be longer and I think the car is much better off not having a locked up tire leave the slick surface and suddenly grab on "good" road causing potential control issues.

    Rumple



     
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