What is the bump-during-braking oddity I keep reading about?

Does that mean that Brake Assist, or its equivalent on the 2005, would leave actual seat belt bruises on passengers, not merely chest pain as DW has suffered in my 2010?

I was unaware that there was any more friction available in the tire-pavement interface to create stronger braking. It felt as if the tires were already pulling gravel out of the asphalt.

 

FWIW, in Consumer Reports tests, the braking distances were no worse on dry pavement for the 3rd gen vs. 2nd gen. Wet was a mixed bag.

For 60 to 0 mph, dry, here are their results in feet:
'10 IV: 133
'08 touring: 133
'04 base: 143

For 60 to 0 wet:
'10 IV: 147
08 touring: 140
04 base: 152

The tires on their '10 were Yokohama Avid S33, size P195/65R15 89S.

 

I slowly worked my way up from 35 to 50 PSI over the period of several months and a change of tires and never noticed the braking bump transition until seeing mention on prius chat and then going out and looking for it.

After several tries I finally found some railroad tracks on a curve at the bottom of a hill so that I could be braking and turning as I crossed the tracks. Normally I'm coasting (no arrows) or light regen (no foot on brakes, foot hovering over gas pedal) and since my foot isn't on the brake pedal I can't notice it?

I tried braking harder and harder each day as I crossed those tracks (but hesitant to brake too hard as there might be cars behind me and I didn't want to wast gas getting back up to speed). Eventually after several tries I found a speed/braking combination that gave me a slight sensation that I could describe as being the one in question. If I didn't go looking for it I would have never found it. I'd guess the front tires were around 45 to 48 PSI when it happened but I didn't check and if I hadn't read about it I wouldn't have given it a second thought.

I suppose if I were in a true emergency braking maneuver the transition might add to the stress of the situation but I can't imagine it ever bothering me under normal driving conditions.

Maybe the effect varies in intensity from one Gen II to another? Maybe only those who are heavy on the brakes to begin with are likely to notice it?

 

I've never really had a problem with this before. Just a few days ago however I did have it (momentary loss of braking) happen to me and I noticed something in particular about the uneven road surface that caused it.

This road surface had a join between a concrete road section and an asphalt section, and the join was uneven (concrete sticking up slightly higher than the asphalt). More importantly however was that the join didn't run directly (perpendicularly) across the road, but rather it ran at about 30 degrees off perpendicular.

I thought that this might have been important because many times previously I've hit irregularities in the road but not noticed the loss of braking so clearly like this time. I'm guessing that the two front wheels hitting the irregularity at slightly different times did something to confuse the traction control. Anyway I'd describe it as a momentary loss of braking, but I can see how some people could mistake it for a "forward surge".

 

Maybe you don’t feel it, but I bet if you had a scangauge monitoring Bta (Hybrid battery amps) you would “see†it all the time.

I am constantly frustrated when driving around the city by just how easily regenerative braking kicks out when you are braking and hit even a moderate bump in the road. You can see the scangauge go from -40 or – 50 (regenerative charging) to positive +3 to +4 (using charge to run the lights / AC etc). I try to let off the brake and press it again to reset it, but unless you press on the accelerator (enough to coast or more) regenerative braking will not reset. Rarely do I have time to get it reset before needing to stop at a light (or whatever).

Given the climate here (freeze and thaw all winter long) the roadways near stoplights are always in sad need of repair. I have learned to “feel†the transition long before the scangauge updates to show it, but it happens a lot and I know it will take a toll on the brakes. Maybe where you all live the roadways before stoplights are nice and smooth, but if they are not, then your just missing it when it happens.

 

That's interesting jpadc. I've often wondered how much regeneration I might be losing when I hit a rough patch regenerating downhill. I didn't know about the problem with "resetting" regenerative braking.

As for why I felt it on that particular occasion and not on others, I suppose it must be related to how hard you're braking at the time.

 

Other people who complain about this issue.
2008 Toyota Prius Traction Control System Problems | | Page 2 CarComplaints.com

It appears to me that some people classify this issue as 'when the regenerative brakes are stopped and you are left with the friction brakes.' Whatever you call it, at least a huge amount of your braking power goes away.I am turning off the traction control soon. This traction control system issue has been one of my biggest complaints with this otherwise great car. It is way too sensitive over bumps. It appears to me that outside of being in the snow and spinning the tires in snow for long periods of time (which can screw up something related to transmission I believe) I am better off with this system off.