Driving on ice or snow experiences, or tips

[Chicken Drumstick]

Your knowledge of ABS is perhaps out of date. I doubt there is an ABS system out there any more that is not at least 3 channels, and many now are 4 channel. In a 3 channel system, the two front wheels are controlled independently, and the rears together. With a 4 channels, all 4 wheels are controlled separately. Even a 3 channel system would work better than what you describe, and a 4 channel would work even better still. What you describe is essentially a single channel system and that would be very ineffective, either with a locking differential or not.

It is reasonable naive to assume everyone is driving a new car....

 

[JustAnOldFashionedLEDGuy]

It is reasonable naive to assume everyone is driving a new car....

As often in these videos, what is happening and what they think is happening is not the same thing.

1998 Cherokee. When you lock the differentials, and you lock all 4 wheels in a stop, the ABS is not detecting wheel slippage, hence effectively, the ABS is not functioning at all. In terms of pure stopping distance, on some surfaces, i.e. snow on top of a slippery surface, you can stop in a shorter distance by locking all 4 wheels compared to with ABS. That is what is happening in this video. Locking the differentials is effectively turning off the ABS. The one with locked differential is stopping faster as the ABS is off and the tires are "plowing", but it is in an uncontrolled skid. You will note it turns sideways while the "2WD" keeps going straight. Initially, when their braking force is highest, the two appear to be stopping in a similar fashion (not exactly). The big difference is towards the end of their braking.

A more modern ABS system would reduce the difference.

 

[Poppy]

I think the question is: Does adding more mass to a vehicle, increase, or decrease braking distance.

 

[fulee9999]

well I don't have a dog in this fight, quite frankly mine is sleeping on my slippers actually
( pictured below )

but as far I know LEDguy explained it well, eventhough alpg88 was ( at least I feel like ) saying the same thing at first...?!

So to my current knowledge modern SUVs or four-wheel drive cars have open diffs all around ( mostly ) so when a wheel on the same axle ( e.g. front ) starts spinning due to lack of traction, the TC detects that, applies brake to that wheel, to sort of replicate a locked diff, giving torque to the non-spinning wheel. An improvement to this is the "sperrdifferential" as we call it here, ot auto-locking diffs / limited slip differentials, which work as an open differential most of the time, but when one of the wheels starts spinning then the wheels mechanically lock together ( either visco or torsen ). And the most "advanced" is when you can manually lock diffs together, either pneumatically or hydraulically, allowing you to decide on your own when and what axles you need locked together, this is the most expensive and rare, but there are kits to retrofit open diffs to be lockable ( most I've seen are pneumatic tho ).

So to sum up, nowadays usually the TC will act as a locking or auto-locking diff, with the difference that a TC can/will limit power to the wheels, so it will feel like you're not going as fast as you can, but much safer than a locking diff like in racecars, where you can plow out of the turn full force.

Or at least this is my understanding, and from this I believe having just TC is the most common and safest way manufacturers make sure that the driver will stay on the road.

Ps.: From my own experience a TC on icy/slippery roads feel like you are held back quite substantially, but also gives you a railcar experience, while limited slip diffs give you a more "fun" experience on traction loss, but can surprise you on corner exits ( a'la BMW ).

Oh and to give an input on Poppy's question, I think you would want the least amount of weight on a car for increased stopping performance, but you'd also want to have a good balance of weight so the rear won't snap out on braking.

 

[JustAnOldFashionedLEDGuy]

I think the question is: Does adding more mass to a vehicle, increase, or decrease braking distance.

Answer is it depends (same answer I gave before).

Dry pavement: more weight will almost always be worse.

Snow: Weight can improve braking and with the pickup truck example, handling during braking as well.

 

[Poppy]

well I don't have a dog in this fight, quite frankly mine is sleeping on my slippers actually
( pictured below )
View attachment 36479

LOL... isn't it amazing how dogs are driven to attach themselves to the stinkingest things, that smell like us?

My dog too, comes into my bedroom to steal one of my socks.

 

[orbital]

I think the question is: Does adding more mass to a vehicle, increase, or decrease braking distance.

+

If on glare ice & already sliding, weight will not help. Very advanced driving to get you out of that situation.
If generally snowy roads, more mass pressing the tires into the road will help.

For the person who said narrow tires are better to get the vehicle down to the road in snow is correct.
Scandinavians proved this about 70 years ago.

 

[Poppy]

Oh and to give an input on Poppy's question, I think you would want the least amount of weight on a car for increased stopping performance, but you'd also want to have a good balance of weight so the rear won't snap out on braking.

While I don't remember the formula for momentum and deceleration, but there are certainly a number of variables involved. One IIRC includes the coefficient of friction, and another mass, and velocity.

Since the coefficient of friction will change with:
1. the slipperiness of the roadway, and;
2. the amount of change that the additional weight adds to the friction of the tires.

I don't know if a definitive statement can be made about all weather/road conditions

 

[orbital]

+

Tires / tire pressure & amount of sidewall matter alot : Tire thread https://www.candlepowerforums.com/threads/tires.481316/

 

[alpg88]

So to my current knowledge modern SUVs or four-wheel drive cars have open diffs all around ( mostly ) so when a wheel on the same axle ( e.g. front ) starts spinning due to lack of traction, the TC detects that, applies brake to that wheel, to sort of replicate a locked diff, giving torque to the non-spinning wheel.

That is the thing, it really does not give extra torque to another wheel, it drops power, and applies brakes. it only makes sure wheels do not slip, yes it will make another side spin, but at the same time it cuts the power and wont help you get out of snow, or mud, it is basically abs in reverse, it even uses the same sensors. it is also a part of stability control systems. but it will not help you in snow the way locking diffs would, not even close.

 

[alpg88]

Actually it is recommended that you turn off traction if you rocking your car.

 

[fulee9999]

That is the thing, it really does not give extra torque to another wheel, it drops power, and applies brakes. it only makes sure wheels do not slip, yes it will make another side spin, but at the same time it cuts the power and wont help you get out of snow, or mud, it is basically abs in reverse, it even uses the same sensors. it is also a part of stability control systems. but it will not help you in snow the way locking diffs would, not even close.

ah, so you're saying that not only does it brake one wheel, effectively directing all the input to the other wheel that has traction, but also cuts engine power in order to prevent the other wheel slipping as well, right?
so in sum, it will stabilize the car, but also decrease the power put down on the wheel(s)

 

[alpg88]

ah, so you're saying that not only does it brake one wheel, effectively directing all the input to the other wheel that has traction, but also cuts engine power in order to prevent the other wheel slipping as well, right?
so in sum, it will stabilize the car, but also decrease the power put down on the wheel(s)

sure, it will help you to take off in slippery conditions, navigate thru occasional patch of ice, gain stability, (if it is a part of stability system) go over wet pavement, but not snow or ice, your car will just bog down. cuz power will be cut due to either wheel spinning, that is why rocking is done with traction off. None of it happens when diff is locked.

 

[JustAnOldFashionedLEDGuy]

Depends on the traction control system. As noted above, most ABS systems are 3 or 4 channel, i.e. they can brake two at the front separately and the rear as one, or they can brake all at once. Since most cars are 4WD, they are only braking the wheel that needs, the one that is slipping. Most front wheel drive cars will also reduce engine power to prevent both wheels breaking loose.

When you combine AWD with traction control, you will always have a 4 channel ABS system, and typically these don't or don't aggressively reduce throttle either, hence they behave more like the 4WD systems. Note that I wrote, traction control has replaced locking differentials on all but a few vehicles. That is because it has. With modern snow tires, modern AWD and modern traction control, these vehicles do well in almost anything you are going to experience on the road including fairly deep snow. You probably aren't going to offroad with them, and true 4WD with locking differential has an advantage in the deepest snow, and hard core off-road. Something like a Touareg is an example of a good modern AWD. People do crazy things with those.

 

[bykfixer]

I have a late model Lexus car with traction control. Yet if anything triggers a check engine light like say a cat convertor is below 95% efficient and the CEL turns on, it turns off the traction control. First time it happened I thought "geez Toyota, did you hire the Ford pinto engineers to design this TCS?" If bad weather is forecast the Lexus stays home.

 

[PhotonWrangler]

I have a late model Lexus car with traction control. Yet if anything triggers a check engine light like say a cat convertor is below 95% efficient and the CEL turns on, it turns off the traction control. First time it happened I thought "geez Toyota, did you hire the Ford pinto engineers to design this TCS?" If bad weather is forecast the Lexus stays home.

Why would a CEL turn off traction control? Wouldn't that be like a seat belt light disabling the brakes?

 

[bykfixer]

Why would a CEL turn off traction control? Wouldn't that be like a seat belt light disabling the brakes?

I asked myself that same question when the cel came on and tcs light lit at the same time. I limped home thinking my car was about to self destruct, did some reading and found "oh yeah that's normal".....