Traction control disabling brakes over bumps

I suspect, strongly suspect, that there is NO condition for which ABS will consistently shorten your stopping distance. Granted, gravel or even snow will be dramatically different, but elongated stopping distances when ABS activated should be a GIVEN, always.

 

The whole point is that it prevents lockup, so you dont skid, you stop. Normal driving conditions make that a shorter speed-to-stop distance then non-ABS with speed-to-skid-to-stop distance. The computer can "pump the brakes" much faster than you can, so any instance where in a non-ABS car you need to pump, ABS will win every time.

 

The downside is that the computer doesn't always make the right call for when to use ABS. Most of the time it is right, and it errors on the side of always trying to keep steering control, so I consider ABS a good trade-off.

Loose gravel is an example where a skilled driver can stop faster than ABS. Locking the wheels piles up loose gravel, which shortens the stopping distance.

Tom

 

If you *want* to skid your abs equipped vehicle on gravel, it takes a bit of practice, but it's completely doable (if your brakes are in good condition). Hit the brakes, the abs kicks in, get off them and then SLAM on the brakes, locking the wheels, as long as there is no slip, the abs won't kick in.

I had to learn this with my subaru, driving in really sketchy places, such as on steep graveled hills where I actually needed to stop, and the abs would not allow it, too steep, seriously.

 

I tried that today with my FJ and it does NOT work. Perhaps SOA has different ABS programming than Toyota

Again, ABS complaints of losing braking over a manhole cover or washboardy gravel roads are also common for the FJ Cruiser. The FJ has electric assist power brakes

Perhaps both the Prius and the FJ share similar ABS programming?

 

Same here.

 

It should be possible to make an ABS kill module. This would work by interupting the pulse pickup from all 4 wheels when the hydrolic brakes are activated. The system would see all 4 wheels as locked, and think the car was not moving.

 

Before I bought my Prius back in 07, I owned a Civic Hybrid for almost 5 years and it did exactly the same thing when a bump caused the regenerative braking to shut off. The first couple of times took me by surprise, but after that it was just routine. So, when the Prius did the same thing it was no big deal.

 

After we got rid of the crappy OEM tires almost all of the traction control issues went away.

 

hey mine does this a lot to and i think i no what your saying about this being scary galownia because when mine does this it tends to "leap" forwards which is a concern, i mean this is my second day with my lisence ima new driver and its scary but you kind of adjust, i had planned on talking to toyota to see if this was a problem but obviously others are expiriencing it as well so i dont know what to say, the only thing is one would think a car wouldnt have a problem like this just as a normal thing but all i can say to you is adjust to it....

 

It doesn't "leap" forwards. This is the human perception of decreased decelleration. You are still slowing down, just not as fast which your body feels as going forwards since you are preparing mentally for increased or constant decelleration. Watch the speedometer next time and I guarentee you it wont go up, it will still go down. Gotta love physics.

Also to anyone that has this "problem" I suggest driving another non-hyrbid car for a couple minutes. Notice how soft the brakes feel like they arent even there. That is what friction brakes are, and that is what it is reverting back to using. Notice in the Prius how when you barely tap the brakes you slam into the windshield, this is the regen braking. So just give yourself the normal stopping distance and apply normal pressure and you will never have a problem.

 

Another case of drivers not understanding the technology. I don't think the brakes are effected at all. Cripes, people have been driving Priuses for years without all these complaints. All it takes is one or two media stories, and now everybody sees a problem with every little quirk.

You are dealing with a car that is engineered years ahead of its time. Live with it, or go drive something else.

 

I always thought the primary purpose of ABS was to allow the driver to retain control [i.e., continue to steer] during panic braking -- not to stop faster and/or shorter.

 

There is a good answer, there is no issue. Also proven by the fact that new tires do not change the outcome.

If you brake hard enough so the friction brakes are enabled it will stop no matter what.

Seriously, now that you have driven your Prius for a bit, just get in another (non-hybrid) car and use the brakes. You will feel as if they are non-existant in the other car. That is how sensitive and strong the Prius brakes are.

Even switching between the RX350 and the RX400h, there is such a difference in the way it brakes and the force of the brakes, we look like fools for a few minutes. Going from the 350 to the 400h, we jerk around and give ourselves whiplash. Going from the 400h to the 350, we scare the crap out of ourselves thinking the brakes have failed.

 

Well, to back up the OP, there is the effect. If it's a problem or not depends on the driver.

With Pearl, I've got Nokian WR tires on her, and whenever she hits a -serious- discontinuity in the road while braking, there is a 1/2 sec. or so pause in braking. Yes it is scary. No it doesn't accelerate during this event. No it hasn't caused me to hit anything or even come close. But then I don't leave my braking to the last second.

Now while I read above it has to do with the ABS (only), -I- suspect it is also partly to protect the HSD from torque shocks.

Just to further the perception issue, it feels to me like it's the shock to the chassis that triggers it, even though I'm pretty sure that's perception only. But it did make me wonder if there was a vibration sensitive part somewhere.

 

This is a good description and similar to my experience with the Gen II Prius.

When we discuss ABS being at the root of the issue, keep in mind that with a regular car you have four wheels braking before the ABS system kicks in. With the Prius, during regenerative braking, you have only the front wheels doing the braking prior to ABS kicking in, and those two front wheels are braking through a differential. This means that only one tire need slip to force a transition into ABS braking. Certainly that will happen more often than with normal four wheel friction braking on a regular car.

Tom

 

OK, the straight answer is no, nothing has been done to "fix" the momentary release of the brakes over rough surfaces, because it was not perceived by Toyota to be a problem. They considered it "normal operation".

That opinion has now changed, however, with all the press about the GIII. Last I heard they were "looking at it" for the GII. Stay tuned, there may be a firmware upgrade.

I don't hold out much hope for eliminating it however, as it is still there on the GIII even after the "fix", from what I've read here. But they may be able to reduce it a bit.

 

Thank you for recognizing and stating so clearly that there is a problem.

This precise problem caused an accident for my wife that totalled the other car and caused us to trade our Prius back to the dealer. Cost to us about $3500 after insurance.

We reported to transport Canada, NHSTA and consumer reports. Transport Canada and CR were kind enough to call back. The dealer was very cooperative