So, this ABS thing...

[hawkeye122]

So back in February, I was driving my Mum's Toyota Tacoma pickup. Bog Standard, cheap, white, single cab, 2.2 liter (The same powerplant as my lightning quick Camry ).

I very desperately needed to be across town for a school event, because, well, I did.
It was Hailing/Snowing/raining, depending on where in the city you were. It wasnt heavy in any way, and wasnt really accumulating. My visibility was more or less fine.

When I was closing in on my destination, there was a 90 degree turn to the left. The hail had stuck to the ground and was about a half inch to a full inch deep, except where the line was where people had driven.

Already aware of the "Dangers" of winter driving, and was approaching the corner at 15 MPH, the road was clear, and the turn was not blind in any way.

Turn in, my direction changes as expected.
Apply brake(~15%)... Slows down a bit, not at all locked. Then, half a second later...


THUD THUD THUD THUD THUD

The whole cabin was shaking, and my car had stopped turning, and I was now going head-on into a fence.
Because I was going 15 MPH, I came to a stop about 12 feet of sliding later.

What the hell? I was braking JUST FINE, going about my business, and then the ABS up and decided I was losing it. I really wasnt! I was in full control of the vehicle, and none of the tyres had locked up under braking. I now refer to the phenomenon as "Premature ABS-ulation".

I really feel that in the snow or hail, that because the ABS likes to engage on its own (This has now happened several times), I'd like to take the fuse out. I honestly think it would be safer without it, since I have a better since of what I'm doing than it does.

In the rain or dry? Yes, it makes sense. But in the snow its just so... difficult. I cant make the car do what I want it to under braking in the snow when it comes on.





Or am I foolish?

 

[homeforsummer]

Some ABS systems do cut in too early, particularly if a brake system is over-servoed. A disproportionately small amount of brake pressure will cause it to cut in if the system thinks there's too little grip.

Usefulness of ABS in the snow is debatable. Most agree that in the snow you're better locking up than having ABS trigger, because snow piles up in front of your tyres and that actually slows you down quicker. Snow sticks to snow better than tyres stick to snow (which is why snow tyres work - they ensure a load of snow sticks to them, which then sticks to the road giving you grip and traction).

However, that's a very particular situation and tends to apply to freshly laid snow. On sheet ice with very little snow, having ABS is probably better than not having it, though of course you'd still drive within your limits. It gives you a little more control when braking by allowing the tyres to roll rather than simply acting as skids.

The part which confuses me about your story is that the car wasn't turning while the ABS was working, when this is exactly the situation ABS is designed to help with - turning in a wheel-locking situation.

I'd ask a few questions based on this:

- What condition were the tyres in? All the ABS or lack of ABS in the world is fairly irrelevant if the tyres simply have too little grip on the road. Whether you think 15mph was an appropriate speed or not, it may just have been too much for that particular scenario, given the grip you had. If the tyres were worn, then ABS would likely cut in early as it may decide lock-up is imminent.

- How can you be sure the tyres didn't lock before the ABS cut in? Again, on very low-grip surfaces, there's often a very fine line between tyres rotating or locking, and it's not always easy to tell where that line is, even with light braking. It's different on dry or wet asphalt, as pedal feel changes, you hear the noise of locking tyres etc. Again, old or worn tyres would mask this further and encourage ABS to kick in early.

- Last thing: I'm not sure how unsophisticated a Tacoma is (body on frame?) but if the whole cabin was shaking that sounds like far more of a reaction than I'd expect from ABS. I've driven several vehicles with ABS and the most I've ever felt in emergency braking is a pulsing through the brake pedal. No shaking, no great noise, just a pulsing pedal. Is the truck in top mechanical condition or is it a bit tired?

 

[hawkeye122]

I dont believe they were locked, based on the fact that I was actively changing direction, and going the direction I expected I would be going as a result of giving the wheel that much lock. Only when the ABS engaged did I stop turning, and just plow straight on. I associated the straight on with the wheels locking, because of the ABS.
I wouldnt have expected the vehicle to turn that well if they were locked.

The brake does tend to feel rather soft. It takes very little effort to bring the vehicle to a swift stop.

They tyres weren't what I'd call "New", but they werent horrible either. Id say about 70% life remaining.

The wheel shook(It needed an alignment, not sure how realted that would be though), the pedal shook, and the whole cabin seemed to lightly knock along with the force. It wasnt violent, but it was definitely new. The sound was also there, it seemed to come from the brakes themselves. It has since been inspected, and the chassis is supposedly good, according to the Dealer/Service center. (It was in a separate accident.) It is Body-on-frame.

I understand the theory on which ABS is supposed to work, but it seems like in the snow/hail, it really didnt. It has come on in the rain, and it worked exactly the way it ought to.

 

[Keef]

ABS doesn't come on unless a wheel is spinning slower than a certain threshold compared to the other wheels. On a slippery surface with crappy tires it's very likely that the inside front wheel locked and slid and you didn't even hear it. You might not feel it either because the outside wheel is the one with all the grip pushing you around the corner. It works via magnetic sensors and is very sensitive. You have to keep in mind that in snow and ice nothing works. Tires lose grip very easily and then the ABS comes on and saps the very last bit of it, often ruining your day. I despise ABS in snow and ice conditions.

I'm surprised it came on at all but not because it was overzealous. ABS typically doesn't work under 12 mph.

 

[MatskiMonk]

My last couple of bimmers have had a tendancy to fire the ABS when I'm braking on an uneven surface, it's annoying but it does no real harm and I'd probably rather have ABS than not given we don't get that much snow around here. It never affects the turning performance of the car though.

 

[Bopop4]

It's likely that you were VERY close to locking up, or had at least one wheel locked.
I find that road vehicles have almost no grip, and in snow and ice even thinking about the brake pedal will get the wheels to lock up.