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Improving emergency braking performance in raining condition

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by A617, May 8, 2014.

  1. A617

    A617 Member

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    Ok so yesterday i had to do an emergency stop at 40 mph after a moderate down pour, here's what happened someone pulled right in front of me and stop in the middle of the road with no time to react I slam on my brakes and to my dismay i felt like was stopping on snow so i had to serve away to avoid the car, luckly no damage to any car, and the the car that stopped took off at an alarming rate. So there's a lot of factors involved in my situation, road condition, tire quality, water accumulation, temperature, condition of brake systems, anyways besides slowing down and been more vigilant (again this is a unforeseen event)...what other options do i have to improve brake performance, im pretty much stock to the bone right now, and second question does low resistance tires have factors in decreasing braking performance, I've never dealt with LRR and im planning in switching to LRR in the future.
     
  2. fuzzy1

    fuzzy1 Senior Member

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    (1) What tires do you have? If original, they may be due for replacement. If they have already been replaced, the brand and model may give some tires guy here a clue.

    (2) What is your tire condition? Miles, or tread depth, or some form of description to tell us how much wear they have experienced?

    (3) What air pressure is in the tires? Low pressures are more susceptible to hydroplaning.

    (4) Did the Brake Assist or ABS or Stability Control trigger in this very wet condition? If not, you may not have been applying full brake force.
     
  3. A617

    A617 Member

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    1) I got the tires Re-replaced by the deader after the originals tires that came with my car as CPO with a weird brand that I never seen before, it developed problems and was leaking nitrogen almost 3 days or so they decided to replace my tires and that was 1 1/2 months ago so current tires Dunlop Signature II with < 1000 miles on it filled with nitrogen
    2) tires is brand new
    3) pressure 49 psi with nitrogen as per service note, and 49 psi with gauge check, i think max psi is 51 psi allowed on tire
    4) My foot as on the pedal as hard i can go, ABS activated during the braking (pedal pulses).
     
  4. hybridbear

    hybridbear Member

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    As far as comparing LRR tires, check out this article from Tire Rack about their testing of different LRR tires.
     
  5. bisco

    bisco cookie crumbler

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    49 psi probably exacerbated the problem. if you're serious, you probably need to replace the tyres with some good stopping power. and lower your psi to 42/40.
     
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  6. A617

    A617 Member

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    Alright I'll reduce the tire pressure.

    How about perhapse wider and larger around 16-17 in wheels, what's the widest tires do you guys run on.
     
  7. Easy Rider

    Easy Rider Active Member

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    YIKES. :eek:

    No doubt in my mind that your excessive tire pressure probably played a small part in the problem that you (almost) had.

    I personally do NOT believe in exceeding the book recommedaion more than 5 LBS or so because more than that changes the tread's perfoamance characteristics too much.
    (Others will no doubt disagree with that.......without any real proof to offer.)

    A panic stop on a road with less than ideal traction is a crap shoot.
    Even with ABS, a little hydro-planning could have occurred.
    If the shower was brief, there could have been a slight oil slick.

    I think it is likely that there isn't much that you CAN do to improve things in that kind of situation.........except maybe slow down and re-think your rock hard tires.

    On a clean, dry road, wider tires might be better.
    On a wet or otherwise slick road, they might be a tad worse.
    It is impossible to eliminate all the bad possibilities.
    Worrying about it won't help either.
     
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  8. bisco

    bisco cookie crumbler

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    i've never run anything but the stock tyres and wheels. perhaps someone with experience can help, or you might try searching tyre and brake threads. all the best!(y)
     
  9. bisco

    bisco cookie crumbler

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    i've never run anything but the stock tyres and wheels. perhaps someone with experience can help, or you might try searching tyre and brake threads. all the best!(y)
     
  10. ive

    ive Member

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    excessive tire pressures baloon your tires. You dramatically decrease the contact patch area. Grip, especially wet grip, is dramatically reduced. Do not exceed the recommended pressure by more than 5 pounds as said here. The ride becomes harsh, grip drops and wear and rattles increase. All for your 1mpg. That accident is not worth it. Even more important, avoid cheapo (chinese) tires. Always get known brand tires with a high silica content. This gives you the wet grip. High silica means higher price, unfortuantly. Cheap tires improve dry grip via soft rubber. They do not last and will scare the shit out of you in the wet. High silica tires dramatically improve grip while using harder rubber. So they last longer, have both wet and dry grip, but cost more. There is a reason cheap tires are called ditch finders. The Prius OEM braking system can get your tires to break traction even at highway speed. So no need to upgrade pads or such bits. Wider tires improve dry grip, but increase the risk of aquaplaning. Your mpg will drop as rolling resistance goes up. Wide rubber beyond a certain width vs. diamter also tends to tramline. This makes highway driving tiresome. A very good tire in the upper price range will offer more braking performance than a budget wide tire and last longer. But you safe the expense for wide rims.

    If you rely on top braking performance, get one of the top 3 tested tires. LRR has a small drop in performance, but the trade if is mainly in comfort. LRR tires are rather stiff.
    Marko


    So drop that pressure and try again.


    iPad ?
     
  11. David Beale

    David Beale Senior Member

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    Want to improve your wet surface braking? Tyres tyres tyres. Overinflation will help mileage but not traction.
    Get good wet weather tyres and inflate to proper levels. You can go 15% over Toyota recommended value and not affect traction. Much more than that will.
    I like Nokian WRGIII tyres and inflate to 40 front, 38 rear. They are "all weather" and also LRR.
     
  12. ursle

    ursle Gas miser

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    So the op has no name tires over inflated and hydroplaned
    I agree, good rain tires and 40ish psi will be safer in deep water, and let me be so bold as to say 40ish is better than 30ish for air pressure in this instance, the higher pressure is more responsive at both turning and stopping.Yes the op could go to 17" wheels with 45 series rubber but why give away 3-4 mpg's.
     
  13. fuzzy1

    fuzzy1 Senior Member

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    High pressure reduces hydroplaning, not increases it. That is according to the aviation and NASA sources that have studied it. I learned about it after discovering that a previous car's recommended pressure was too low for my rainy climate.

    But that doesn't cover wet grip absent hydroplaning, which is a separate issue. Despite plenty of strong opinions, I've seen no consensus on this.
     
  14. Easy Rider

    Easy Rider Active Member

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    You can't make THAT flat statement either......as the effect of higher pressure on the tendency to hydroplane depends almost entirely on the tires construction and tread pattern.

    All other things being equal, a narrower tires has less tendency to hydroplane but it is not a guarantee that higher pressure will create a smaller contact patch.
     
  15. SmellyTofu

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    To give you more shorter braking distance? To give you more cornering grip to swerve away from a hazard? To avoid the trauma of a crash? To avoid injury in a collision? To avoid the headaches of dealing with insurance? To avoid the inconvenience of not having your car when its away for repairs? ... to save some tiny amount of money?
     
  16. SmellyTofu

    SmellyTofu Average punter

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    Double post
     
  17. ive

    ive Member

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    get proper rubber with a good wet traction rating (high silica content = high price) and dump them after 4-5 yrs the latest. The rubber gets hard with time and grip gets worse. Wear actually goes down. So folks tend to use them forever as there is still thread left. Wnna kill yourself, get cheap chinese ditchfinders witha 60000 mile warranty. First drop of rain and you think you're in a sled on ice. There is a reason good tires cost serious dosh. Dry grip is not an issue anymore except for the most bizzare brands. On wet roads the differences show. Some budget brands compensate lower silica content, high silica =? high wet grip) with softer rubber. The price you pay is wear rate. So medium priced tires with good wet grip wear fast. Higher priced tires tend to offer both wear resistance plus grip. You pay your money. Buy cheap, slide twice.


    iPad ?
     
  18. Former Member 68813

    Former Member 68813 Senior Member

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    Overinflater or not, this is how ABS works. Allows you to steer around obstacle. Sounds normal to me.