How Powerful the Brakes Really are...

There are MANY reports that have the speed of the Lexus at, or near 100mph. Whether this was from doing the physics, or whether it was from the 911 call (where the caller himself said they were travelling at 100mph), I have no idea. The report estimates, at impact, the Lexus was going about 100mph. If there was any partial braking, it was minimal, at best.

I find it odd that there is no mention in the report that any of the airbags in the 2009 Lexus deployed....YET...the report does specifically mention the seat belts were buckled and in tact. Why no mention of any airbag deployment? An oversight in this report?

 

See, that's where you're wrong. Read up a number of posts the recommendations from Consumer Report. This thing has gotten so much press and concern from driver's, they've come out with their own recommendations (steps) to stop a run-away car. Good for them. As they mention, in many cars, if you turn you car off while accelerating, you could lose both steering and braking. This is absolutley the LAST thing you want to do. As far as I know, the driver of the Lexus did turn off the engine (but was still accelerating because he was going downhill). Maybe his brakes weren't working as effectively because he turned off the power? Furthermore, putting the car in to neutral will do nothing to slow the vehicle when going down a steep hill (as seem to be the case with this Lexus).

But I would ask you the following - Why is any of this not worthy of discussion? Are you more concerned with talking about what color of prius to buy? Would that be better "karma"?

Finally, the vast majority of drivers have absolutley no idea what works best for them, or even the best way to stop a run away car? You certainly didn't know, if you think turning off the engine is a good idea. It might work for some cars....but for many other's, a very bad idea. In almost every case, a person's knee-jerk reaction will be to slam on the brakes. And 99.999% of the time, those brakes will stop a run-away car. I would add - keep your foot on the brakes, and don't pump them, as that will do nothing to cool the pads, and could result in excessive heat build-up and ultimate fading of the pads. But I'm sure you know all this...so i guess I'm wasting my time?

You might not like the "negative karma"...but actually, I believe the discussion is a useful one to have. If the negative karma bothers you, why are you reading? There's no shortage of fluff, or "good karma" thereads on this site, that quite frankly, I find to be mind-numbing. Read those, instead.

 

Exactly. I sense bad "karma". LMAO.



But back on topic, C&D gives the best advice...and for those that think (??) they know it all, then advise they skip this link:

How To Deal With Unintended Acceleration - Tech Dept. - Auto Reviews - Car and Driver

C&D Summary of Steps:

(1) Hit the Brakes

" Certainly the most natural reaction to a stuck-throttle emergency is to stomp on the brake pedal, possibly with both feet. And despite dramatic horsepower increases since C/D’s 1987 unintended-acceleration test of an Audi 5000, brakes by and large can still overpower and rein in an engine roaring under full throttle.

Camry: From 100 mph, the stopping-distance differential was 88 feet—noticeable to be sure, but the car still slowed enthusiastically enough to impart a feeling of confidence.

We included the powerful Roush Mustang to test—in the extreme—the theory that “brakes are stronger than the engine.†From 70 mph, the Roush’s brakes were still resolutely king even though a pinned throttle added 80 feet to its stopping distance. However, from 100 mph, it wasn’t clear from behind the wheel that the Mustang was going to stop. But after 903 feet—almost three times longer than normal—the 540-hp supercharged Roush finally did succumb, chugging to a stop in a puff of brake smoke."



(2) Shift to Neutral -

"This is your best option in an emergency. Neither the Camry’s nor the Infiniti’s automatic transmission showed any hesitancy to shift into neutral or park when accelerating at full tilt. (Automatics have a piece of hardware called a park pawl, which prevents the transmission from actually engaging park and locking the wheels at speed—it creates a disturbing grinding sound, but the car essentially coasts freely.)"


NOTE: Will not stop acceleration down an incline, and with some older transmissions it may be difficult, or even impossible to go from "D" to "N" while moving.




(3) Turn it Off -

"Switching off the ignition is a sure way to silence an engine, but it’s probably the least desirable action because it will also make the car more difficult to maneuver. It causes a loss of power-steering assist, plus it will cut off vacuum boost for the brakes.The new wrinkle here: the keyless, push-button start-and-stop systems in many vehicles. Owners need to be aware that these systems require a long press of the button to shut off power when the car is moving (3.3 seconds for the Camry)"

 

Disagree all you want, but C&D is correct. It's fact that some cars, if you turn the power off, you lose either, or both power steering and brake boost.

To be clear, C & D is writting to all cars. Not just the Camry. With some cars, what they say applies, and to others, it will not. The statement "It COULD lose power steering, etc...." applies. But I doubt the average driver has any idea whether it applies to them, or not.

What amazes me is that many folks on this cite take a general statement and assume it applies to all cars, all the time. Please. If it doesn't apply to your car, then fine.

Ever own a 1986 (or 1984?) Subaru wagon with wide snow tires? I did...and you needed it...BIGTIME! Lost complete power on the highway years ago...I struggled to just get it over to the shoulder. Can't imagine that a smaller person, a frail person,. or many woman would have done?

Whatever works for you, go with it. But the fact remains, if you continually "pump the brakes" down a long incline, or over a long period of time with heavy application...most brake pads will fade. You can believe what you want, but I know this to be true from first hand experience, and through various performance driving schools i have attended.

If you want to elliminate (or greatly minimize) the risk of fading, put in ceramics. I use them on my Jag and I get no sense of fading after heavy, heavy use on the track.

On this we agree.

 

So, a 465 foot drop in approximately 2 miles (straight line) representd about a 2.5 degree grade. Not steep.

I was thinking about this last night...If, as the report said, he was going about 100 mph at impact...and let's say his terminal velocity along the road was somewhere between 130mph-140mph (at some point does the rev limit kick in?). I still have a hard time rationalizing that if his brakes were functioning even partially, he couldn't drop his speed by more than 30-40 mph? Even with faded brakes, I would still have expected to bring it well below 100mph...maybe not be able to fully stop the vehicle, but at least something much less than 100mph. I'd also like to know (since it was not mentioned in the report) - did any of the air bags go off at impact? If not, why not?

 

Which post are your referring to as being flawed?

Anti-lock braking systems are exactly what they say they are...they are a brake system that prevents wheel lock-up (ie, "anti-lock") by modulating the brake pressure/force. The modulation is done in a fraction of a second. That said, at speeds in excess of 100 mph+, it's not clear the wheels were ever at a point of locking-up.

While anti-lock brakes will bring you to a stop in SLIGHTLY shorter distances than the same car without anti-lock brakes (not always, though), the primary benefit of anti-lock brakes is - you can still steer the car. In cars without this system, once the wheels lock up, you can't steer and are at the mercy of where your momentum will take you.

From every report that I've read, it would appear that one (or all) came into play: (1) Complete brake failure, (2) Inadequate braking pressure (possibly due to loss of power, pressure leak, etc?), and/ or (3) severely faded/distorted brake pads/rotors.

#3 could, would result from extended use (time wise) of the brakes while trying to stop a car speeding at over 100mph. Brake fade would be greatly exasserbated if the driver manually pumped the brakes - this extends the total braking time, and allows for more heat built up, and temperature rise to occur.

STRONGLY disagree. I do it periodically, and have had zero issues. Do I accelerate up to 100 mph, keep my foot on the gas while applying full brake pressure until it comes to a complete stop? No, I do not. But I will routinely test the brakes under the following conditions, with NO ill-effects: Find a straight section of road, with no traffic. While going 50 or 60 mph....slam on the brakes to similate a panic stop. In the instances I do not have my foot on the gas (also), I will bring the car to a full stop. In cases where I do have my foot on the brake, I usually release once I'm down to about 20mph. For me, it gives me a bench mark on my brakes. i know what they can do, and know what they should be capable of. I'll do this once ever 6 months. I check my brakes regularly, and performing such tests will not warp your rotors or melt your pads. If they do, you have other issues that need to be looked at. Not speculation. I know for fact because I continually check my brakes. I've done this with all my cars: Honda, BMW, Saab, Jag and now Prius. Geez.

But to be clear, I'm not here to tell anyone what to do. I'm on this site to learn, and (hopefully) inform. There's an aweful lot of mis-information floating around, and if i can help to contribute to debunking some of it, then I feel I've been of some help. But I will say this - If people actually tested their cars more, and knew what they can do under extreme situations, I suspect we'd have fewer fatalities. Pilots and race car drivers have to do it all the time - test (or simulate) actual emergency situations. That way, when/if the real thing comes up, they have a better chance in taking the right action. But I suspect this is the wrong crowd to be talking to about this, as Prius owners aren't excatly known for their driving prowness.

That's why there is an investigation. But until the investigation is complted/released, it's Toyota who is taking the heat.

Based on what I know, the unintended acceleration aspect of this clearly points back to toyota. But why this driver could not even slow the vehicle to below 100mph, raises a number of flags for me. IMO, multiple systems would have had to simultaneously fail. The other possibility is driver error. I do believe that had he been pumping his brakes going down this 2 mile incline at speeds of over 100mph, could very well have warped the rotors and melted the brake pads...thus contributing to his inability to bring the vehicle down to a safe speed. It is also quite possible that this being a rental car, the braking system (mainly pads and rotors, but also fluid) was not properly maintained....which then points back to the rental company/dealer...and NOT Toyota.

Two problems in this mystery: (1) What caused the unintended acceleration and (2) Why couldn't the driver (even) bring the vehicle down to a safe speed, let alone stop the car? If I had to guess, #1 is Toyota's fault, but #2 is either, or both the driver and/or dealer's fault. I guess when this goes to court, blame will be assessed, and we'll know as much as can be inferred from the physics and forensics.

 

OK, sorry for the confusion.

I don't know which models, or even which years this would apply...but would suspect it applies to older models. But the fact still remains there are cars on the road where you would lose either, or both power steering and vacuum boost if the power is turned off. But even if you still had some steering and some braking action...if you're in a situation like this Lexus owner was, clearly, you need all the braking and all the steering you can get. The very last thing you want to compromise, when trying to control the vehicle, is the steering and braking. That's my point, and was also C&D's point.

That's one thing I still need to test with my Prius - turn off the engine while driving to see how it feels and handles. I've done the panic stop, and I'm very comfortable/satisfied with how the brakes bring the car to a stop. Will the stopping distance be longer (how much) if I turn the engine off?