California Prius Update: Wear pattern on brakes raises doubt | Hacker News Reader

California Prius Update: Wear pattern on brakes raises doubt

online.wsj.com

9 pointsMikeCapone28 comments

I'm not sure I agree with the article's conclusion, although I'm convinced the guy is lying. The basic fact presented is that the brakes show no sign of heavy use, but of course they don't: the brakes are more powerful than the engine, so if they were applied heavily, the car would have stopped. But the fact that they don't show signs of heavy use doesn't necessarily mean that he wasn't stomping on the brake pedal. The whole point of his accusation is that there is something wrong with his Prius.

As I said, I'm convinced he's lying, but to show that they'll need to provide evidence that the entire braking system was working, not just that the brake pads aren't worn down.

Are brakes more powerful than an engine at full speed along with the car (large mass) moving at high speed? Brakes are designed to slow a car not under power.

Car and Driver magazine had a great article a few months ago in which they tested breaking several different cars (including one of the recalled Toyotas) from 70 mph down to zero -- both with the throttle behaving normally and with it forced to full on. In most cases, the brakes are plenty capable of stopping the vehicle at full throttle (the exception was a 540-hp Roush Stage 3 Mustang travelling at 100 mph with the throttle locked -- in that case, the breaking distance was tripled to a total of ~900 feet).

http://www.caranddriver.com/features/09q4/how_to_deal_with_u...

One of the interesting points in the article was that the Toyota Camry -- with throttle forced wide open -- stops in a shorter distance than a Ford Taurus without any issues.

On the other hand, the article also points out that at 100 mph, it wouldn't have been immediately obvious that the breaks were working, even though they were (though at 70, you would have felt an immediate effect).

The point curiously missing from the C&D article is that a car driving a full throttle will also be generating only a tiny amount of manifold vacuum. In most cars, more vacuum is necessary to provide the power-assist to the brakes, once any stored vacuum is used up. (The brakes will work, but losing power brakes for the average driver will be an upsetting event, especially with a stuck throttle.) They mention "don't turn off the ignition because that will cause you to lose brake assist", but fail to connect the no vacuum at wide open throttle to the same end result.

I'm sure the C&D test drivers were willing to mash the pedal and generate the best braking force the car was capable of. The average person, confronted with a stuck throttle, lost power brakes and the resulting "hard" brake pedal may very well not be able to summon the force required to generate full brake pressure. (It's an amazing amount of force compared to what you're used to using. If you're also the type to worry about flipping the car from putting the car in neutral, you're probably not going to bend the seatback applying enough brake pressure to get the job done.) I think I'd have expected better than the average driver from a trained highway patrol officer, though.

You can't have it both ways. Either drivers are pushing the pedal as hard as they can (which every single driver reports) or they aren't because they're scared.

Either way, your argument is based on a bad assumption. At full throttle in a non-super or turbocharged vehicle, there is still more than enough vacuum to assist in braking.

Another point I didn't mention. The Prius can detect a no-assist situation and will reroute all braking pressure to the front wheels for maximum effectiveness. So even in the extremely unlikely situation you have no regenerative braking and no vacuum assist, you can still stop the car.

have you ever seen a burnout?

Yes, but the brakestand type burnout procedure does not use full braking.

In a safe location, in a rear drive car with an automatic, try the following:

In drive, heavy brake pressure with the left foot, roll into the throttle with your right foot. Get to full throttle (over a second or two; don't take forever), and gradually release some of the brake pressure.

You'll find a sweet spot where the torque of the drivetrain is able to overcome the rear brake(s) and spin your right rear tire (or both of them if you have a tight limited slip diff). Your partial pressure on the front brakes, which are not driven, will hold the car stopped. You can further come off the brakes to let the car rollout of the burnout, or get out of the throttle and stay put.

Obviously, this is far harder on the car than driving to the corner store for some milk, but it's an effective way to clean off the tires at the dragstrip, a good way to get attention at the local teen hangout on Friday nights, and a great way to get a ticket for "ostentatious display".

"During the 911 call, the operator urged Mr. Sikes to shift the car into neutral. He later said he was afraid doing so might cause the car to "flip" or shift into reverse."

Maybe a driving test should be re-instituted every few years, or at the very least make sure that drivers have a basic grasp of physics...

Well most people don't know enough physics to understand that.

I love the mythbusters episode that debunked the Nazi soldier on the bike flipping over in the Indiana Jones movie.

People tend to not want to try new things when their car is not working properly. Maybe there should be driving simulators so that drivers can practice recovering from unexpected events without risking injury. It works for airplane pilots.

Basically, why guess about what to do in a crisis when you can try recovering from the crisis as many times as you want beforehand?

But isn't shifting into neutral common taught and common knowledge I know my driving instructor, videos, and both my mother and father told me this when I was learning to drive.

Trying it and seeing that you don't die is stronger than "heard it from my dad".

In Denmark, as a requirement to get a drivers license, you have to go to a closed driving circuit and do brake and avoidance maneuvers at different speeds and go on a skid pad. Feel how the car reacts on the limits.

A standard drivers license test is done in a manual transmission car (which is what most people there drive anyway). I also think that using a manual transmission helps to understand how a car works.

I will say that I took my Subaru out yesterday intending to try and switch to neutral, this after hearing about this controversy, and it took a monumental act of will to actually do it. I was really scared that I would shift into reverse and harm my car. Finally decided to pay heed to my fears and didn't do it until after I had tested just how much pressure it takes to do the switch while standing still with my feet on the brakes.

I don't mean this to say that I defend Mr. Sikes, but the fact that reverse is just one up from neutral is kind of scary. Just how careful would you have to be to avoid doing the shift? Is there a check in the system that prohibits shifting to reverse if the car is moving forwards?

Modern automatic transmissions will not switch from forward gears to reverse abruptly. They even won't engage a lower gear until your speed is low enough so the engine doesn't over-rev. Even virtually all manual transmissions have interlocks preventing an accidental shift into reverse (though this is a very difficult mistake on a 6-speed).

I can't speak for the Prius, but my Grand Prix has a shifter with a button that I have to depress to go into any gear _except_ neutral. I can just slap at the shifter and pop it into neutral without any fear that I'd over-shift into reverse.

I'm pretty sure that this feature is standard on every modern car that doesn't suck (i.e. everything we have here in the States). I've yet to drive a car that didn't have it.

You weren't in any danger though. If your car were stuck at full throttle you might feel differently.

A few years ago my car's throttle did get stuck (not a Toyota, due to my own stupidity) and after a few seconds of shock the thing that seemed most rational to me was to pop into neutral and apply the brakes. It worked just fine.

I remember hearing somewhere that cars won't let you go into reverse above a certain speed [citation needed].

Try this for full version: http://www.google.com/search?q=%22Interstate+8+near+San+Dieg...

Thanks, I'd like to see people start putting a [sub] tag or something similar in the title for pages that require a subscription.

You're welcome.

Although WRT to subscriptions it can get tricky. E.g. the Financial Times will let you read 1? or so articles per month without registering, free registration gets you 10? or so per month, then you have to pay.

Murdoch's Wall Street Journal doesn't make it easy for a subscriber to know which articles are directly free and which aren't: some of the news items that are in the class of this one and some (recently fewer) of the OPED pages are free. But if not, if you do a Google search like the one above and then click through you get the full article, despite his grumbling about Google et. al. Go figure.

I think the guy is being paid by Toyota. One dramatic case regarding this highly publicized recall turns out to be a fraud; casts doubt on the entire ordeal and wins the public back over to Toyota. Genius.

If they were clever enough to do that, they probably would've handled the situation better so far.

I hoping we'll find out this guy shorted large amounts of Toyota stock the day before or works for a competing car company...

This article comes to an abrupt...

I feel that we should avoid submitting articles like this.

See my recent comment on how a subscriber can't easily know if a Wall Street Journal article is free or not and how you can easily see all of one anyway.

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