Braking problem

Re: Braking problems especially on wet roads

This phenomenon is well known, and is the result of a loss of traction during braking. Loss of traction causes the Prius to transition from regenerative braking to ABS friction brakes. During the loss of traction the car does not "leap forward", but it feels this way since the braking force is momentarily reduced. It is completely normal and doesn't cause a significant increase in braking distance, other than the usual trouble from any slippery road surface. If you have a lot of trouble with this, you may want to consider better tires.

Tom

 

Re: Braking problems especially on wet roads

qbee42 is absolutely correct. I think there are several posters here who have mentioned this, and the car does not "leap" at all, it is merely the friction brakes taking over. I suspect once people have been in varying weather and road conditions you will learn how this acts. As always with any car and road surface conditons with rain, you need to adjust your braking distance and how hard you apply the brakes.

 

Re: Braking problems especially on wet roads

Sadly, to my mind, this leapy feeling is well known. It will happen when you are applying the brakes going over a rough/bumpy road. My route to work takes me down a hill with a stop light at the bottom. I have learned to be careful here because inevitably I lose traction and get this transitional experience. Even though I'm prepared for it, I don't like it. I'm not looking forward to when the road is icy.

 

Re: Braking problems especially on wet roads

Low rolling resistance tires are a contributing factor. Everything that makes a tire good for braking makes it bad for mileage. The Goodyear Integrity tires that shipped with Gen II Prius were especially bad. I haven't heard how well the Gen III tires are working.

Tom

 

Re: Braking problems especially on wet roads

Stay with the recommended tire pressure to reduce such occurance over the bumps

 

Re: Braking problems especially on wet roads

My road is in poor shape, you can't avoid the bumps which sets up the loss of traction. (another reason why some people make reference to MASS-HOLES). This happened when I first got the car and the pressure was 32/30. I'd read about it here, so while I was surprised, at least I knew what was going on.

I upped the pressure after 2 wks to 40/38 which is well within the tire rating (44). I can't say it happens any more or less now. It's consistent in the same places.

 

I really hope I never have to experience this behavior while driving in the rain on a wet and slippery road.

Are there any known reports of accidents resulting from the temporary loss of braking momentum? Has Toyota ever officially commented?

 

You won't be driving it much, then, because it's not going to be fixed. This is Toyota's way of telling you that you're driving too fast for conditions. Do any or all of: slow down, use longer braking distances, buy grippier tires.

 

Re: Braking problems especially on wet roads

Actually, not quite true all the time Tom. But close.

My Nokian WR (now Nokian WRG2) have much more traction than the OEM tires, but also give better mileage. Bonus, they are excellent rain tires and perform well in snow and cold. Oh, and did I mention they don't wear any faster than a "summer" tire?

But yes, even with these "best tires" I experience the above brake pause (which is what I like to call it), mostly triggered by bumps, but it can also be triggered by a transition to friction brakes from regen. and even from VSC interacting with traction control and anti-lock braking.

For me, it lasts about 1/2 sec, causes momentary panic, but the car still stops just fine. If 1/2 sec. of lost braking causes you to stop "long" you are leaving your braking too late!

Just wait until you get on ice. Garbage tires will cause the anti-lock to let the car run long without skidding (you can steer just not stop). Better tires are the only fix for this.

You'll get used to it. If it's a big problem get better tires. I love the way the car handles poor traction.

 

There are numerous reports of accidents from temporary loss of braking due to slippery road conditions. We especially have trouble with this in the winter. It is not unique to the Prius, but common to all vehicles relying on friction with the road surface.

Tom

 

Re: Braking problems especially on wet roads

I *knew* I would get nick picked with this one. The engineer in me wanted to qualify the comment with "most of the qualities", but I left it off for brevity. Oddly enough, the old Goodyear OEM tires are not really LRR tires, although they do have terrible traction and fairly good mileage.

Nokian seems to one manufacturer that has managed to get good traction and good mileage. I'm due to replace my Micheline tires this fall, and I am planning on using Nokian WRG2 tires as well.

Tom

 

Re: Braking problems especially on wet roads

You won't be disappointed! After reading all the complaints of poor handling of the GII Prius I was shocked when, on the way home from getting my WRs, I was surprised by a corner in the road (sign was knocked down). Pearl went around the curve, which was rated at 50 km/hr (I found out later), at 80 km/hr. No noise, no drifting, we just went around the curve. If I had still had the "Integrities" I would have been off the road!

 

Right...Difficulty in braking due to tires loosing traction vs an apparent complete pause in braking from the switch of regenerative braking to friction brakes are two separate issues for me.

Have there been any reports of accidents resulting from the temporary loss of braking due a switch from regenerative braking to friction brakes?

 

Re: Braking problems especially on wet roads

I don't understand your last statement.

1/2 second at 20-25mph is an entire car length.

 

Re: Braking problems especially on wet roads

MASS-HOLES, that's funny.

 

Your rationalization does not make sense.

Are you saying a temporary loss of braking is a result of driving too fast ?

 

Temporary loss of braking is caused by the tires momentarily losing their grip on the road. Notice that smooth dry roads can have sand on them. The notion that the car shuts off braking effort for any perceptible length of time (*) while the brake pedal is applied is absurd.

(*) this is, for more than a few milliseconds during ABS action

 

Re: Braking problems especially on wet roads

Is "nick picked" the same as "nit picked"?

On a more serious note, the Nokian WRG2 seems to be an excellent all-season tire.

But note that Consumer Reports' most recent tire tests published in its November 2009 issue show at least two tires that seem to be better choices overall and are a lot cheaper to boot (the Nokian WRG2 is pricey at about $160 per tire in the 205/60R 16 size used by Consumer Reports in its tests):

Michelin Primacy MXV4 equals or outperforms the Nokian WRG2 in every single category -- including snow traction, ice braking and rolling resistance -- and costs about $122 per tire.

Hankook Optimo H727 equals or outperforms the Nokian WRG2 in every single category -- including snow traction and ice braking, but excluding rolling resistance where it rates a little lower -- and costs only about $96 per tire.

Here's a reprint of the Ratings Charts for the tires tested in Consumer Reports November 2009 issue:

Consumer_Reports_Nov._2009_Tire_Tests-1.doc

 

Re: Braking problems especially on wet roads

Damn! Nit picked about nick picking. I'm really having a bad day. I think I'll use jayman's approach and have something to drink.

Tom

 

Re: Braking problems especially on wet roads

Interesting! Right now I am running Michelin MXV4+ Energy tires, which were the predecessor to the Primacy. I may have to rethink my choice.

Tom