Do I have a valid brake issue in my 2017?

is it in the transfer from regen to friction braking under 10mph, or rough pavement at any speed?

 

I have experienced the same braking sensation as you describe in my 2016 since new. It is certainly different in the Gen 4 than previous Gen 3 or Gen 2. While disconcerting, I do not consider it to be anything more than an idiosyncrasy for this Gen Prius.

 

Thanks for explaining that. I've had the "slip" occur at higher speeds... at approx 30 mph, if I happen to brake on a fairly slippery surface like one of those steel construction plates. But I don't believe it's ever happened on any rough pavement, and there are a ton of those around here in So. California. I will make a note of exactly where I am, next time it happens.

Just another Prius oddity....

 

I have felt that. I think it is the momentary shift to traction control. The brakes take a split-second off, but get right back to work.

 

Yes. I forgot about the traction control. Never had that in any other car. Thanks.

 

It may be picky to quibble between "traction control" and "ABS" (it's the same computer under the dash that does both, as well as generally running the brakes), but "ABS" is the function that kicks in when you are braking and the computer detects possible slippage (which is what, from the computer's point of view, might be happening if you are lightly braking and hit a bump or pothole and one wheel-speed sensor value jumps).

Compared to a conventional car with ABS, a Prius has an extra step it has to go through at that moment. Under light braking, it probably isn't using the friction brakes at all yet. It is braking through the drive train only, which is a traction disadvantage because it only acts on two wheels. The car has to switch as quickly as it can to release the regen braking of those two wheels (to be sure traction is maintained) while it brings the four-wheel friction brakes into play. You do notice it for a split second, and if you give yourself time, you learn when to expect it and it doesn't surprise you.

It doesn't happen in urgent braking situations, because the computer detects those and goes straight to friction braking anyway.

This is one of the oldest and most-discussed consistent things for new Prius owners to learn about, throughout all Prius generations from the very first. After buying my Gen 1, I learned about it by reading about it right here on PriusChat. (I even read about it here before I had ever experienced it in the car, so I went out to a nice low-traffic bumpy road and just made it happen several times until I had taught myself what it was like.)

A little more detail is here.

Enjoy your car!
-Chap

 

Yes, agree - it's because there is an extra step in the braking procedure. I read somewhere that it can be up to 80 or 90% of braking in a PRIUS is by regenerative braking - depending on your environment and driving style (or am I thinking 80-90% less brake wear?).

I think there is another aspect - ECO tyres, I don't believe have as good grip or progression of a high-performance tyre. I have noticed it when I've accelerated up a hill with one front tyre on a painted lane-marking, it will spin briefly before traction control intervenes. Similarly, braking if I hit a painted line while braking.

2 articles by Tony Schaefer on braking particularly pertinent to PRIUS, or hybrids:

Braking » What Drives Us

Try to Avoid Braking Altogether » What Drives Us

 

On my old Gen 2 with the original tires I constantly got the traction control light when I hit a manhole cover and with new tires it didn't happen as much. I don't notice this with the Gen 4 but I do notice that little bump sometimes and just take it as a Gen 4 quirk but I have never noticed any lights lighting up.

 

Thanks all for the links you guys provided. Good reading. Alan mentioned painted lines, and somebody else said bumps in the road and potholes can trigger the ABS / traction control. Now I remember, I have experienced that weird slip feeling in all 3 of those scenarios. So it's good to finally know what's going on. Thanks very much.

 

For the most productive kind of insomnia, keep in mind that ABS and trac/VSC are two, distinct, functions of the brake/skid computer. ABS is what's kicking in when you have the light brake-bump-lurch effect. It doesn't light the traction-control light because it isn't that function. And it doesn't require that any tire actually lost grip: only that the computer thinks that could have happened, because all four were spinning along nicely at the same wheel speed but then one hit a bump or hole and its speed changed for an instant when it rolled a different distance than the rest.

-Chap

 

I had the traction control kick in one time, with a very loud "thunk." The two front wheels were in water, and spun; the rear tires on dry pavement. It worked well.

2.5 years after purchase, and I'm still learning new things about this Prius. I read all the articles in the links. Very interesting. All this time, I have not been driving (or braking) my Prius to the best of its ability to maximize fuel efficiency. Kind of hard to do in the daily heavy traffic, but this car is capable of much more.

I usually just drive it, not too concerned with achieving high mpg. You can drive this car very hard and still get over 50 miles per gallon. Maybe that's why I see so many people speeding in a Prius? Tony also discussed the pros & cons of increasing the tire pressure. I might give it another try, see how long I can deal with the bumpy/harsher ride. (After everything I've been thru with these Michelin tires, they still don't feel right!)

Try eating 2 eggs and a banana for insomnia.

 

Sometimes it comes down to diminishing returns. The $avings from hypermiling with a V10 Viper or V8 LandCruiser and saving 10% is a $ub$tantial amount - 20% $aving is close to the national deficit. But, already using only 4.1l/100k, a 10 or even 20% improvement in fuel is really only Petty Cash.

 

As I said in another thread, I think the hypermiling becomes a game or a serious hobby for some Prius owners. Maybe even an obsession?

You bring up a good point, the overall savings is probably fairly minimal. I know my car is capable of better gas mileage, but realistically I just don't have the patience to do it all the time, and the traffic is just too heavy in my area. I am perfectly satisfied with a 600 mile tank and 55 MPG. But I could drive my car more modesty, certainly more efficiently with less strain on the ICE.

But putting 50 psi in the tires? I don't think I would last one day! I like my teeth to be intact.

 

I agree - not 50. I put 40 in and that was too rough - I settled for about 38.

 

I suspect extreme tire pressures hasten wheel bearing and suspension failures.

 

I just found a quote in this thread, One hack I would like to see | PriusChat, that explains the sensation I was describing above, "Quick taps on the brake pedal will bring the pads into contact with the disk, though with continued pressure they’ll back off as the hybrid system adjusts torque between MG1 and MG2." I'm not sure if this is the sensation the OP was asking about due to all the subsequent discussion of ABS intervention, but it explains perfectly what I have noticed under light braking in my Gen 4.

 

Is it just me, because as a former motorbike rider, I always ease off the brakes when about to put a wheel on a manhole cover. Certainly, none of my bikes had ABS on the front wheel, (or any wheel for that matter).

 

Especially when in a curve. Doubly so in rain.

 

It's a basic error you'll only make once with a big bike. Unless you're a sucker for punishment!!!!