How do you brake in an emergency?

Discussion in 'Gen 3 Prius Main Forum' started by Higgins909, Dec 4, 2018.

  1. Higgins909

    Higgins909 Junior Member

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    10' 169k Trim level 3, stock tire size and rims, door jar PSI. Chitty Douglas all seasons. Checked out the rotors and pads and they look pretty new. I don't know what it is but it feels like my brake pedal is more random with input to braking force, that I kinda have to pulse the pedal to brake smoothly. This is way more noticeable in the rain. There are a particular set of bumps, that if I hit while braking, my braking kind of cuts out. I'm not sure if it's just the regen or what.

    Today I nearly rearended someone. Was going about 45mph-50mph and the car up front was wanting to turn, who was also in front of the truck that I nearly rearended. I was using regen to slow down, then I realized that wasn't gong to be enough and got on the physical brakes and then I noticed we were coming to a near complete stop and got on it more. ABS kicks in and it feels like I'm not stopping anymore so I back off a bit and back on and after a bit it lock up again for a second but stops and it was too close for comfort, even though I still had a few feet between us. I was really worried I was about to rearend someone. It wasn't even that bad in a way, I don't know why I locked up some wheels.

    Should I have just braked harder despite locking up other wheels? It felt like when ABS started working I was slowing down less. I've tested ABS before in the rain trying to stop as fast as possible. ABS just seems to make your car shake like heck and slide more then backing off ABS. Today it was 55 F out and my tires were fairly warm and road was dry. (It didn't rain but the road looks kinda weird in my dashcam) Later on after this incident I checked all my brake pads as there is some squealing under heavier breaking that I've noticed going on for a long time. (making sure a wheel wasn't braking with metal on metal) After inspecting I went for a test drive and tested my brakes on a few different roads and they were working pretty good then.

    How do you brake in a emergency?
     
  2. bisco

    bisco cookie crumbler

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    start by leaving more distance between you and the car in front of you

    in an emergency, hit the pedal hard and keep it there

    for normal braking, pulsing and feathering work. the prius brakes will grab when wet, so be wary

    you will get the feeling of loss of breaking when traction control kicks in over potholes etc. just keep pressing.
     
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  3. jerrymildred

    jerrymildred Senior Member

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    When ABS kicks in, the last thing you want to do is back off on the brakes. Unless you're a professional race car driver and have lots of practice with the particular car you're driving, ABS will pump the brakes way way better than a human can do it.

    On a bumpy surface, there are plenty of reports of ABS kicking in because the tires lose grip hopping from bump to bump. Try braking hard on a washboard road sometime for a bigger thrill.

    HARD! I stomp on the brakes and press as hard as I can. Just had to do that in the rain a couple weeks ago when a Ford pickup died in the center lane but was hidden by the other land yachts between us. There was no way around and by the time I realized that it was more than just a tailgating induced slowdown, its was two feet short of being too late for me, the car in front of me, the one behind me, and probably 50 others. When I came back that way a couple hours later, the truck and the boat it was towing as well as several other cars were off on the shoulder. There's a reason you're supposed to allow at least 2 seconds following distance and increase it in poor traction or visibility.
     
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  4. fuzzy1

    fuzzy1 Senior Member

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    The usual wisdom with ABS is STOMP, STAY, STEER. STOMP the brake pedal as hard as you can. STAY on the pedal and continue pushing as hard as you can. STEER where you want to go.

    Here are a couple interesting (and old) commentaries I picked up ---

    From a fire-rescue industry columnist:
    "When ABS first gained popularity in everyday automobiles ... I would often be called to investigate accidents that involved elderly drivers. These drivers had been driving for 40 or 50 years with traditional, non-ABS-equipped vehicles. I would often ask these drivers what caused the crash, and I always got the same answer: “Officer, the other vehicle pulled out in front of me and I slammed on my brakes. Then the brakes stopped working.”

    Upon further investigation, I would ask what made this person think their brakes stopped working. The answer was always the same: “As I put my foot down on the pedal, the brake pedal started thumping.” In reality, the brakes were working fine. The problem was that the ABS was engaging; these drivers had simply never experienced this type of situation. Instead of leaving their foot down and steering around the hazard, they took their foot off the brake and ended up in an accident."

    From an auto industry product launch and training series:
    "These subjects/drivers unknowingly participated in an informal, blind tally of their braking and steering abilities. ...

    ABS – Of 147 drivers, 62 did not engage the ABS on the first try, extending the braking distance beyond the ABS potential. 42% crash potential first try. By the fourth try only 12 did not. Some quick commentary from the drivers; (a) blamed the car ..., (b) that they didn’t want to hurt the car (as if a crash wouldn’t), (c) some drivers pumped the brakes (d) most braked as hard as they thought necessary, less than effective.

    Steering – (several types of curves, different radii and swerve maneuvers, across varying frequency and size bumps and wetness) Of 143 drivers, 3 used push-pull, shuffle steering (all three were trained, during their teens in the U.K.), 78 used either one hand or “pretzel steering” (palming the wheel or locking crossed arms), 140 used hand over hand, 21 used underhand steering (reaching across to pull down the inside of the wheel on the opposite side), some used combinations.

    Results
    Out of 286 runs through the course, knocked-down-cones represented 97 separate crashes, the majority due to the inability to ABS brake-and-turn effectively and simultaneously. ..."
     
    #4 fuzzy1, Dec 4, 2018
    Last edited: Dec 4, 2018
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  5. Maarten28

    Maarten28 Active Member

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    Had that happen to me once or twice too. Basically, regen braking does not brake very hard and when you are focussing on the regen, you lose sight of the distance to the car in front of you.
    I would say (and I do that too): keep more distance when you want to focus on regen braking or do not focus on regen braking.

    But in an emergency situation: push the brake pedal as hard as you can.
     
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  6. Tideland Prius

    Tideland Prius Moderator of the North
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    Just release the accelerator quickly and stomp on the brake pedal. Brake Assist will determine its an emergency stop and assist in additional braking force if it thinks you're not pressing the brake pedal hard enough. If you let go then brake again, BA won't kick in and you'll be relying on the power of your legs (and the brake booster/ABS etc) to provide braking power and I'm not sure most people actually press hard enough. They think they are but they're not.
     
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  7. Sporin

    Sporin Prius Noob

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    Agreed.

    -------------------------------------------

    As with many things discussed on the internet, I think a lot of you guys are over thinking it. I don't know or care whether I'm using Regen or Friction braking. When I need to stop, I push the brake pedal. When I need to stop really quickly, I push the brake pedal harder and faster. That's really all there is to it.
     
    #7 Sporin, Dec 5, 2018
    Last edited: Dec 5, 2018
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  8. Mendel Leisk

    Mendel Leisk Titanic Social Director

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    Have you had this car since new? How many miles on it. Are you following the US maintenance schedule, specifically: full inspection of brake, every 3 years or 30K miles?

    I'd recommend also a brake fluid change, at the same interval. This is ignored in the US schedule, is in the Canadian schedule.
     
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  9. Robert Holt

    Robert Holt Senior Member

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    Appreciate the reference with driving data!
    “Shuffle steering” was new term for me. I THINK I understand it and its advantages in avoiding arm injury in airbag deployment, but is it as quick and precise in emergency evasion maneuvers as , say, hand-over-hand steering? What do professional drivers use?

    Thank you for bringing up that Brake Assist system! After 5 years I finally had that system actually engage in a hard deceleration scenario a few months back and was rather taken aback that the Prius’s ECU had decided to do a maximal stop rather than the sub-maximal deceleration I had planned on. No harm was done, but I will warn you that having maximal deceleration occur is quite risky in congested traffic situations, particularly if you are being tailgated, and could cause a following driver to rear-end you. Better than hitting the car in front, of course, but still not optimal.
     
  10. fuzzy1

    fuzzy1 Senior Member

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    I first triggered mine just a few months into owning my 2010, on a city street when the car in front made a sudden stop midblock for invisible cause with all brake lights out. That lack of brake lights delayed my response, so I needed a full panic stop to avoid a collision, and it worked. Fortunately, the car behind me also stopped in time.

    In nine years since, I've tripped BA only a few times, usually in response to cars in other lanes suddenly encroaching on my lane with little to no space. When it trips on dry road, it feels like the tires are trying to dig out the asphalt.
     
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  11. AzWxGuy

    AzWxGuy Weather Guy

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    My major complaint about the process has to do with the advantage most other drivers will take as you attempt to maintain a safe following distance. There is just something so enticing about that 2-3 car length space in front of you where they just have to pass and get on in there. That will bring me to a boil pretty quick. I know that, in the grand scheme of things, these drivers will eventually eliminate themselves from the driving pool. Hopefully they do so with minimal impact on the remaining courteous drivers.
     
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  12. Higgins909

    Higgins909 Junior Member

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    I remember one time brake assist gave me a bit of whiplash. The light turned yellow and instead of slowly increasing the brakes, I went immediately to a medium braking and brake assist decided to lock up my wheels. I don't think I ever put the brake pedal near the floor compared to my Honda, where it was normal. Brake Assist messes with the way I like to brake, or used to like to brake... or maybe sometimes still brake. Not really sure how to explain it... would probably be long and confusing, but it's smooth and fast and not too hard that I would cause any issue for the person behind me.

    10" Prius 169k (almost 170k) probably due for a oil topoff around 170.5k. I got it with 163k in Jan 2018. (Think that's the right month) This car was taken care of by Toyota and some of the latest logs I remember when I looked were about the 120k service and spark plugs being changed. The Prius manual doesn't seem to give me a what needs to be done at what mileage interval like my Honda or any of the motorcycle or truck manuals I've looked up before. Will try to take another look at it soon.

    I assume the dealer did tires and brakes and oil before I bought it. (Slapped the cheapest tires they could find on it)

    I do and don't care about regen braking too much. I like to keep a safe distance and be able to brake in a longish smooth way. (hate that stop and go stuff where I can't seem to brake smoothly because other people brake harder then expected)

    This is what happened. I've played with ABS in the rain before with this car and decided I didn't like it and that I could break faster without it. (Car was like hopping and sliding instead of braking) That is why in this video I let off the brake slightly when ABS kicked in and got back on it. I also got the sensation that when ABS was going off that I wasn't slowing down as fast anymore. I've also read in the manual that ABS doesn't work as well in the rain or something like that. In the video it doesn't looks that bad but in the moment I was really unsure if I was going to stop in time. Next time I will try to let ABS and Brake Assist do more. I don't think I even braked that hard.
     
  13. ChapmanF

    ChapmanF Senior Member

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    I can't be certain from your video, but if there was a little bump, manhole cover, or the like as you were slowing there, it's possible that all you noticed was the car switching from two-wheel to four-wheel braking. That regularly startles people who are new to the Prius.

    To understand what's going on there, there isn't any need to talk about ABS (which lots of cars have), or traction control (which lots of cars have). One thing a Prius has that isn't the same as lots of cars is a braking mode (regen) that only uses two of the four wheels. When you are braking gently or moderately (as it looks like you were doing), the car's first choice is just to use regen.

    Little bumps and potholes and manhole covers trigger a quick switch from regen to "normal", hydraulic, friction braking. That's because those road irregularities cause wheel speed sensor signals that, as far as the computer knows, could mean that you're near the limit of traction (even if that isn't really what's happening, and it was just some little bump; the computer has no way to know that).

    If you're near the limit of traction for two wheels, the obvious first thing to do is to double the rubber grabbing the road by using four wheels to brake. If you were near the traction limit before, you'll be quite safely down near half the traction limit after. That's even without involving ABS or TRAC, just simply doubling the rubber doing the work.

    The car has ABS, and VSC/TRAC, and they could kick in as a further step if there are still signs of iffy traction after simply switching to four wheels. But usually they don't, and aren't needed, and just aren't involved in the transition you're probably feeling here.

    Typically, all that happens on a pothole, etc., is the regen braking lets go, and the four-wheel hydraulic braking grabs on. Those two things happen in that order, because if the computer thinks you could be losing front-wheel traction (needed for steering as well as braking), priority 1 is to make sure that doesn't happen. It brings in the hydraulic brakes at the same time, but they weren't applied before, and it takes a tiny split second before they make up for the same amount of brake force you had been getting from regen.

    You write as if surprised that something like this happened when you were only braking gently or moderately, but in fact, those are the only times it ever does happen. If you are braking more urgently, the computer detects that (by the pedal angle sensor detecting your speed on the pedal), and goes straight to four-wheel braking for that stop. The stop in your video looked like a pretty ordinary, rather than emergency, stop.

    So the little regen-to-friction "whoopee" only happens during non-urgent stops when there is some kind of road irregularity, and there isn't anything special you need to do; just keep your foot on the brake and press a smidge harder to make up for it and come to a stop at your originally intended point. With familiarity and practice, it completely stops being startling.

    -Chap
     
    #13 ChapmanF, Dec 8, 2018
    Last edited: Dec 8, 2018
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  14. Higgins909

    Higgins909 Junior Member

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    In the video I don't think I used Brake Assist at all. I usually max out Regen, maybe a little more (I judge by sound and feeling. Can't hear it over music in video) The only thing not normal about the stop in the video is that I locked up 2 times under only moderate braking. I should have been using all brakes at the time. (Regen looks like I'm not even braking in video) I can't remember for sure, but I think there was a sensation of not slowing down quick enough even though I was increasing the brakes. I wonder if the switching from regen to friction was happening.
     
  15. ChapmanF

    ChapmanF Senior Member

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    Are you convinced you locked any wheels? I thought the weather looked fair and the pavement dry. Did you leave any skid marks?

    (At the moment, youtube videos are silent for me, so if there were telltale shrieking-rubber noises in it, sorry, I couldn't hear them.)
     
  16. qdllc

    qdllc Senior Member

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    The Prius is different in that a computer decides what to do when you hit the brakes.

    Speed + pedal pressure = regen braking vs. physical braking.

    Varying pressure while emergency braking will confuse the car in what you want to do. Just mash the pedal until you know you can let up.
     
  17. Higgins909

    Higgins909 Junior Member

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    Happened again a couple days ago, on the same road, but quite a bit further down the road. It had been sprinkling on and off all morning 55~ deg F. I went out for lunch. I was doing about 40mph and was planing to turn right. I started slowing maybe 150ft away (probably something way different) as I was getting closer I noticed I wasn't slowing down fast enough so I pressed a little harder and nothing and running out of room I'm still increasing and ABS kicks in and I essentially slide half way though the intersection before letting off the brakes.

    I don't think I got below 15mph. I try again in about 400 ft at the next right, this time I only get up to 30mph before I start to brake and it's nearly the same exact story, but this time when ABS kicked in I put the pedal to the floor. (No one was behind) After a second or two (what it felt like anyways) the car started shaking from ABS (I assume all 4 wheels locked) Was down to 2-5mph and made my turn...

    I don't understand if it's just that slick out or if my tires are just junk in these conditions. (I still haven't gotten new tires) The parking lot I turned into looked dryer and even though I didn't really test it, it seemed less slick. Maybe it's that particular road? (The parking lot was like a bumpy black look while the road was a smooth white rock)
     
  18. Grit

    Grit Senior Member

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    Sounds like your hiding the type of tires and surface that’s left on each of the tire.

    If I had bald tires and stomped on brake to stop with vengeance, this would confuse ABS and id be in a ditch.
     
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  19. fuzzy1

    fuzzy1 Senior Member

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    A quick calculation suggests that stopping from 40 mph, in a distance of 150 feet, requires a coefficient of friction of 0.36. I'm accustomed to foul weather conditions with much less traction than that.

    Combine worn thin-treaded tires tires, very smooth road surface, lubricated a bit by some oily grime, and adding some rain, and I'm not surprised that you slid through the intersection. You need good tires, and to allow more stopping distance on smooth slick surfaces.

    But I'm not guaranteeing that there isn't a brake problem, you might have something. Just pointing out that from what I've seen in aggressive dry climate driving cultures, this result is not necessarily a surprise even with good brakes.
     
  20. Mendel Leisk

    Mendel Leisk Titanic Social Director

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    Is that documented? It could be, but I'm just wondering if there would be some application of the rear brakes as well.

    I had the experience of driving a car with one rear brake inoperative (after a dealership brake fluid replacement) and it was really messed up: trying to come to an uncomplicated stop behind the white line at a red light, the ABS started activating and I ended up in the middle of the cross walk.
     
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