Prius 2013 skids while driving today

Since you haven’t mentioned...Check all tires to see if they they are the right tires for weather driving conditions and check all psi levels. Next measure all tires’ tread, if all are 2mm or less then get new tires.

All extensive replies with tire tread technology and tire engineering answers are welcome below.

 

Extensive Tire Engineering Reply: less tread means greater contact patch; OP didn't mention rain/water on the road.

OP: could this be a "black ice" situation? Especially since you were on a bridge, which freezes before the road.

 

A bridge, in 26F weather, or even low-mid 30s early in the morning, is a classic icing condition, even if you can't see the ice. That is why it is called "black ice".

Do you have much winter snow and ice driving experience?

The old 2/32" rule (and law in most states, except dry southern outliers) is outdated for winter conditions. (2 mm = 2.5/32") The modern advice is a minimum of 4/32" for winter. On All-Season tires at that depth, I start getting uncomfortable with braking performance on ordinary wet roads in my climate zone, particularly on sections that have lost their texture under heavy traffic back in previous summer heat and become glazed smooth.

 

Yeah, welcome to black ice and frozen bridges..scary as all *ell, especially if never been previously experienced. Then again, scary as all *ell even with previous experience.

Many years ago, (in a RWD sports type convertible) I was passing through Texas, heading toward Charleston, SC and rolling along on CC at about 80 with almost no traffic. Felt like a pretty mild winter night. Had a long gradual left sweep ahead of me and noticed police lights way, way ahead and more lights even further away, so I turned off the CC and started slowing down. The first set of lights was a PO waving his arms up and down motioning to slow down. I remember thinking WITW, I'm already down to ~30. Once I got a lot closer to the second group of lights, and a lot slower, you could see about 6-7 cars piled up where they just went straight instead of following the sweep. I'd never been so happy to see police lights, or I would have been #7 passing through a patch of "black ice". Scary stuff and not very predictable. Rattled my cage a little bit and I ended up pulling off the highway and getting a hotel room for the night. Decided to finish my trip after the sun was up for a while. Been a bit paranoid about ice ever since.

 

Here's another vote for black ice. If you've ever been in a major earthquake, that about the level of control you feel when on black ice. Hard to spot, usually forms on bridges first, and provides all the tractions of ... well, ice. Even if you know it's there, you often can't control the car. I once did a near instantaneous 180 on black ice and came to rest on the grave shoulder with both left tires popped off their beads.

 

About 15 years ago I was got on the interstate in town to make the 8 mile drive to my rural exit. Driving an older AWD Honda CRV, and since the road was dry I did the usual, put the cruise control on. 6 miles later, on a dead level stretch of road, I hit black ice, still with the cruise on. EVERYONE knows you don't use cruise on ice, but there WASN'T ice when I started off, and I failed to notice it. Anyway, the revs went up, and the nice person end kicked a little out to the side, no problem, I killed the cruise and steered into the near skid, piece of cake. BUT THEN, the automatic thingie that kicks in the rear drive (normally it was a front drive), while i was still pointed somewhat sideways and before the revs had dropped, and that was all she wrote. I got behind the cycles of the swerves, they exceed my command authority lets call it, and once on the shoulder, with some gravel, ever so gently and slowly went over sideways. No injury, seatbelt on, it was all in slo mo. I had earlier noticed a surge in traction a few other times, when that AWD kicked in it was sudden and hard to predict, and could lurch you into a cattiwampus situation. Turned out this was a common issue, there was a very specific Honda rear end fluid you MUST use to prevent this, using otherwise would make the AWD jerky and slow to engage. The radio gear heads Click and Clack enlightened me on this about 6 months after the fact, it made me feel a bit better about my winter driving skills anyway.
I love my Prius in most winter conditions, but black ice, real slick black ice, all bets are off. Right now my beater '99 RAV4 with it's new Michelin IceX tires, hasn't left my shop, all my winter driving so far, in mountainous Idaho snow country, has been with the Prius.

 

Possible fixes or exchange of camp fires stories?

 

Only fix I know of is road salt. Or sand on the ice.

 

Camp fires FTW!

I've experienced pilot-involved oscillation on land in two different vehicles:

The first time, I was a kid, on my bike. I had a neighbor with a really long straight paved driveway that just cried out for seeing how fast I could go. It was great, but about halfway along I noticed just a little tiny shift in my balance. No problem, corrected that, tiny bit too much, now a tiny wobble the other way, no problem, corrected that, slightly bigger wobble now the first way, corrected that.... In real time it was pretty quick: woopwoopwoopwoopwoopwoopWoopWOOPSPLAT off in the grass at the side of the drive. I never forgot that weird dawning realization that my own reaction time was a key part of the resonant system and that there wasn't a thing I could do about it (other than do my best to choose where to splat).

The second time was decades later, in a 4WD Bronco II during a snowstorm. The traction seemed ok, everything felt pretty secure, and then I think I must have hit a small patch of ice under the snow. Just enough to put me at a tiny angle off from straight ahead. No problem, corrected that, nice easy and slow, now just a tiny bit off the other way, fixed that, nice easy and slow ....

Because the truck was so much more massive than the bike, the oscillation was way slower ... it was almost stately. Instead of woopwoopWoopWOOPSPLAT it was more like wooOOOOoosh...wooOOOOoosh...wooOOOOooshWooOOOsh and by then I had the same realization that my reactions were part of the oscillator, and that I had maybe at best the choice to end up on the south or north side of the road. The snowdrifts looked bigger and softer on the north side and there was no oncoming traffic at the moment, so I managed to get a 180 to happen and thump backwards with the right quarter into the north snowdrift. Not even a mark on the paint. Pulled back out on the road, turned around, and finished the trip ... waaaay more carefully.

This is something that has always puzzled me. I am pretty sure I have made trips with cruise on, over mostly dry pavement with occasional icy patches. They were all in older vehicles with no fancy VSC, just old-fashioned cruise control.

In all of those cases, when I passed over ice, the cruise did what I expected it would: it held the wheel revs constant, because that's what it does; it doesn't have any other way to sense road speed. If I had not had cruise on, under my accelerator pedal input the wheel revs would have increased until I noticed traction was lost and backed off. The cruise reacted a lot faster than I could, and pretty much kept the wheel revs right at the road speed setting so at the far end of the ice the wheels still pretty much exactly matched the pavement.

Since those days I've noticed that there does seem to be a large internet consensus that cruise is bad overall in changeable traction conditions, and I'm willing to believe there could be sound explanations behind that, only a lot of places the advice gets repeated, the explanations seem to get left out or botched. Too many places say the problem would be the cruise driving the wheel revs higher, which of course is exactly what old-tech cruise control does not do.

I guess one difference could be that the old-tech cruise usually only knew the speed of the driving wheels, because the speedometer sensor was in the transmission. In a modern car with wheel speed sensors at all four corners, cruise might really notice the road speed decreasing, based on the signals from the non-driving wheels, and that might lead the cruise to increase power, as the internets seem to believe. On the other hand, it would then see the driving wheel revs exceeding the non-driving ones, which would be a pretty clear signal to stop doing that.

Maybe it also matters just what's on the road. The dry-pavement-with-ice-patches scenario might be best-case for having cruise on, because nothing slows the car down much as it proceeds over the ice, the cruise keeps the wheels at set speed, and at the far end of a short ice patch it's pretty much like nothing even happened.

But if it's ice under snow, or enough water to hydroplane, that stuff probably is going to slow the vehicle down, and in that case the cruise keeping the wheel speeds constant would mean now they are above the road speed.

 

Great descriptions, @ChapmanF! Glad you survived.

This isn't ice related. More like stupid related. Your bike adventure reminds me of a tank slapper I witnessed back in my college days. But instead of the handlebars slapping the tank, the tank was slapping the handlebars. My best friend and I went for a motorcycle ride. This was back in the days of cables and drum brakes. His front brake cable had a broken strand that sometimes would snag. He was always able to release it with a quick squeeze and release of the brake lever ... until he wasn't. I was behind him when it locked up solid. We were only doing about 35 and he was wearing a jacket he'd borrowed from me and a new Bell helmet of his dad's. The back end of the bike went from side to side trying to pass him. After several cycles of that over the longest three seconds he ever experienced, the back end finally passed him and there he was sliding along behind the bike. His only concern? "If I scrape my dad's helmet, he's gonna kill me." So he put his arm under his head to protect the helmet, thus grinding through my jacket and a pretty big part of his left forearm. But, praise God, the helmet was unscathed.

As there was no significant damage to the bike, he very carefully rode back home, cleaned and bandaged himself and then replaced that cable the next day.

 

That’s definitely weird. Where are you getting that info, directly from the tires, or reported on some invoice? Are they the same brand/model? Are you first owner? Can’t imagine that being from factory, or even most tire shops.

The difference will mean you’re running slightly smaller OD tires on the back, if confirmed.

I’d chime in about overpasses being more prone to ice up, and sooner: they lack the thermal mass of a road on the ground.

 

The antilock brakes are expecting the same size tires on all four corners. Mismatched sizes probably didn't cause the skid, but may have contributed to the severity of your skid. There is no memory function so we can't know what the car was reading from the wheel sensors at that time but you can be sure it was reacting as if all four tires were equally sized.

 

Just for curiosity looked up defenders (OP hasn’t disclosed tire specifics beyond size and speed rating), and that combo exists.

 

With fronts and rears of this mismatched menagerie at 5/32”, time for new?

 

Hmm ... if the VSC activated, it does retain freeze frames of values from the most recent 4 (?) times it activated. I've looked at mine in Techstream.