Snowy Freeway Mountain Pass - VSC vs Center Diff Lock

[flintknapper]

Front and rear both lock left and right together at their respective ends. Center locks the rotational speeds of the driveshafts together. In a corner there are 4 different rotation speeds occurring. The tighter the turn, the more this comes into play. Notice you leave 4 separate tracks in the mud/snow/sand when cornering this shows that your tires are traveling different paths and therefore different distances. Try locking your CDL and making a full lock turn in reverse on a high traction surface (clearly not what we're coving above). You will very quickly feel your driveline bind up. If you push it, one of two things will happen, a tire will break traction or a mechanical failure will occur. The diff exists for a reason.

I'm not interested in further interweb argument so I'm not touching the engine braking comment.

^^^^^ This is correct....and requires no argument.

Many folks misunderstand the relationship between the T-case being locked (driveshafts forced to turn at equal speeds) and the differentials at the axles (open diff still operates as before, locked diff acts the same as a locked T-case). And then there is the indisputable fact that the front tires take a different 'track' than the rear tires in a turn (meaning the front and rear tires are turning at different speeds as well as the outboard tires on each axle).

The physics @RedHeadedStepChild alluded to is solid information. HOW this manifests as 'handling' in snow or other low traction conditions can vary widely.

 

[Hokie LX]

This comment about NOT using the transmission is interesting to me. I always use the transmission to help when I can but In snow I dont down shift I usually leave the truck in 2 or L depending on the speed. I would like to hear more about this

I'll touch on this briefly.

Have you ever downshifted at a mid-high rpm range and feel the truck pulse forward as it downshifts and all the weight goes forward when the RPMs spike? We all probably have... Now imagine this on a icy surface. When this happens and there is a sudden jolt on the moving tire, it can lose traction on an already dicey surface causing you to go out of control. Specifically the rear end losing traction with the weight transfer from the sudden slowing of the vehicle. Similar to stabbing your brakes in the snow and you feel the rear end get loose.

Now this does not happen all of the time but the risk is there when you engine brake on icy surfaces if you downshift an the rpm's get too high suddenly. FWIW, I'm not some veteran snow road driver but I did live in Buffalo, NY and experienced lots of lake effect snow and other dodgy conditions so I do have some decent experience driving in poor winter conditions. I personally do not engine brake in snowy/icy conditions. Some common sense when braking and not stabbing the brakes will slow the vehicle just fine in poor conditions, especially when paired with a good set of tires!

 

[krice118]

I'll touch on this briefly.

Have you ever downshifted at a mid-high rpm range and feel the truck pulse forward as it downshifts and all the weight goes forward when the RPMs spike? We all probably have... Now imagine this on a icy surface. When this happens and there is a sudden jolt on the moving tire, it can lose traction on an already dicey surface causing you to go out of control. Specifically the rear end losing traction with the weight transfer from the sudden slowing of the vehicle. Similar to stabbing your brakes in the snow and you feel the rear end get loose.

Now this does not happen all of the time but the risk is there when you engine brake on icy surfaces if you downshift an the rpm's get too high suddenly. FWIW, I'm not some veteran snow road driver but I did live in Buffalo, NY and experienced lots of lake effect snow and other dodgy conditions so I do have some decent experience driving in poor winter conditions. I personally do not engine brake in snowy/icy conditions. Some common sense when braking and not stabbing the brakes will slow the vehicle just fine in poor conditions, especially when paired with a good set of tires!

Thanks thats what I was guessing. I have driven in a fair amount of snow, hearing others methods never hurts! the 100 is incredible in snow.

 

[Hokie LX]

Thanks thats what I was guessing. I have driven in a fair amount of snow, hearing others methods never hurts! the 100 is incredible in snow.

At least that's my experience/opinion on the topic. I love the 100 in the snow! I drove a 2011 Tahoe Z71 for a while in Buffalo as well and I feel more comfortable/confident in the LX. I never had trouble with it in Buffalo...even when we had snow part way up the vehicle doors or black ice.

 

[CLEcruiser]

Lots of people like to say abs and vsc are no good. But the truth is 99% of drivers are not better than the sensors and ecu's controlling the car. I would say leave CDL off, rely on the vsc.

 

[Spike555]

Front and rear both lock left and right together at their respective ends. Center locks the rotational speeds of the driveshafts together. In a corner there are 4 different rotation speeds occurring. The tighter the turn, the more this comes into play. Notice you leave 4 separate tracks in the mud/snow/sand when cornering this shows that your tires are traveling different paths and therefore different distances. Try locking your CDL and making a full lock turn in reverse on a high traction surface (clearly not what we're coving above). You will very quickly feel your driveline bind up. If you push it, one of two things will happen, a tire will break traction or a mechanical failure will occur. The diff exists for a reason.
@RiverRatMatt is correct. Subaru and others use dynamic diffs to get the best of both worlds.

I'm not interested in further interweb argument so I'm not touching the engine braking comment.

No one is disputing the fact that the tires track differently in a turn. No one is disputing the fact that locking the front and rear driveshafts together and making a tight turn on DRY pavement binds up the transfer case.

What I am saying is, when driving on a snowy road, you are not making turns tight enough to bind anything up or to cause a wheel to loose traction because of any binding. When was the last time you made a u-turn in the middle of the road?
Can a wheel loose traction on a snowy road? Yes. Will having the CDL engaged cause this to happen on a road? Very very doubtful. Could it cause it to happen during a u-turn on a snowy road? Yes.
Again, lots of snow, not just a dusting, if you need extra traction engage the CDL, you don’t have to, but it helps.

 

[MountaineerLC]

I'll touch on this briefly.

Have you ever downshifted at a mid-high rpm range and feel the truck pulse forward as it downshifts and all the weight goes forward when the RPMs spike? We all probably have... Now imagine this on a icy surface. When this happens and there is a sudden jolt on the moving tire, it can lose traction on an already dicey surface causing you to go out of control. Specifically the rear end losing traction with the weight transfer from the sudden slowing of the vehicle. Similar to stabbing your brakes in the snow and you feel the rear end get loose.

Now this does not happen all of the time but the risk is there when you engine brake on icy surfaces if you downshift an the rpm's get too high suddenly. FWIW, I'm not some veteran snow road driver but I did live in Buffalo, NY and experienced lots of lake effect snow and other dodgy conditions so I do have some decent experience driving in poor winter conditions. I personally do not engine brake in snowy/icy conditions. Some common sense when braking and not stabbing the brakes will slow the vehicle just fine in poor conditions, especially when paired with a good set of tires!

Good points! I agree that engine braking is not optimal for slowing down on slick roads. I will add that engine braking is effective to keeping your speed controlled before you get too fast to start with.

For example, I crossed three snow covered mountains today. At the crest of each I downshifted into 2nd and let the engine help control my decent. This kept me around 25 mph with only minimal brake input. No need to ride the brakes for 2 or more miles at a time.

On a side note, I did not use or need CDL. I don't think I even slipped a wheel.

 

[dividedan]

DO NOT use your transmssion to slow you down on icy roads, this will send you into the ditch. You will cause your tires to skid doing this. Engine braking only works on dry roads. So don’t do it.

Can you explain this? Having a hard time seeing how it is different that using your brakes from a physics perspective.

 

[krice118]

Can you explain this? Having a hard time seeing how it is different that using your brakes from a physics perspective.

The point here is if you are in normal driving, D, and are going say 45 if you shift down into 2nd the car will jerk as the RPMS match your new gear selection - this is not very graceful (on dry pavement this isnt going to affect anything and is ok for the transmissino) just like if you quickly stabbed the brakes on a wet / snowy surface.

You can use the engine to assist in braking but I would suggest for around town in bad snow leaving the transmisson in 2 and not touch it and gently apply brakes etc.

Snow driving is all about being as graceful wit your movements as possible - not jerking the wheel, dont floor it in turns, dont be aggressive on the brakes etc..... so same goes for the transmission. Again most of this advice is extremely cautious

 

[Ninja Cruiser100]

Yah I thinks the pixie dust in all this discussion is:

1. Thoughtful measured movements and inputs are important.

2. Proper/good tires trump electronics.

3. Common sense > stupidity.

 

[dividedan]

The point here is if you are in normal driving, D, and are going say 45 if you shift down into 2nd the car will jerk as the RPMS match your new gear selection - this is not very graceful (on dry pavement this isnt going to affect anything and is ok for the transmissino) just like if you quickly stabbed the brakes on a wet / snowy surface.

You can use the engine to assist in braking but I would suggest for around town in bad snow leaving the transmisson in 2 and not touch it and gently apply brakes etc.

Snow driving is all about being as graceful wit your movements as possible - not jerking the wheel, dont floor it in turns, dont be aggressive on the brakes etc..... so same goes for the transmission. Again most of this advice is extremely cautious

I see what you’re saying. I’m thinking about it coming from a manual transmission perspective where you can match the revs and make a smooth transition.

 

[Live to Ski]

Hokie lax nailed it.

This from a 20yr ski patroller/Alta refugee (did I say 600" avg yearly snowfall). Always be in lo prior to the need. Anticipation/fear is your friend.

 

[Spike555]

Can you explain this? Having a hard time seeing how it is different that using your brakes from a physics perspective.

Now here is another one to confuse you...shifting the transmission into neutral when trying to stop on slippery roads helps you stop faster, this removes the power from the wheels so the brakes only have to overcome your momentum and not the engine power plus momentum.

It is the same as pushing in and holding the clutch pedal on a manual transmission car.

And like others have said, dropping your auto transmission into a lower gear on slippery roads causes a sudden gear change at the wheels and can cause them to loose traction, no traction means you’re heading for the ditch.

Starting off from a dead stop use the 2nd gear start feature, this starts the transmission in 2nd gear and slips the clutch to get you moving and prevents wheel spin.
Just leave your transmission in drive, press the 2nd gear start button and let it do it’s thing.
If you know you need engine braking stop, select the gear you need and start down the mountain.

 

[rake]

What model year did vsc first appear on Landcruisers? I have a 1998 LC and if it has stability control, it's news to me. I have to admit I really don't understand what the AWD on the Landcruiser means. One wheel in front and one rear wheel have power when center diff is unlocked? In snow, I usually drive my Subaru, which seems to have better traction.

 

[Spike555]

What model year did vsc first appear on Landcruisers? I have a 1998 LC and if it has stability control, it's news to me. I have to admit I really don't understand what the AWD on the Landcruiser means. One wheel in front and one rear wheel have power when center diff is unlocked? In snow, I usually drive my Subaru, which seems to have better traction.

Your Subaru is all wheel drive, the Land Cruiser is full time 4x4. There is a difference, I’d try and explain it to you but the engineers would throw a sh!t fit for me not using all of the correct terminology in the exact correct way, so you’ll have to Google it.

Your Subaru is lower to the ground so it’s center of gravity is lower and it will handle better in the snow because of that.

The stability control uses the brakes to try and prevent a skid, it does not work, all you get is beeping and flashing warning lighs on the dash. You’re skidding because you lost traction, using the brakes to try and gain traction does not work. You’re not missing anything.

 

[rake]

Spike555, another question I hope you can help with. You stated you can drive at any speed with the cdl engaged (not dry roads). My previous vehicle was a 2001 Nissan Pathfinder. The owners manual said I could shift into 4 high at speeds below 50mph. I've searched for a similar speed restriction for engaging the LC center diff lock but found nothing. Are you aware of any speed restrictions on the LC for engaging the cdl? Also, is shifting a 4x4 into 4 high the equivalent of engaging the cdl on the LC? And thank you for sharing knowledge with folks like me who are still new to this.

 

[RiverRatMatt]

Your Subaru is all wheel drive, the Land Cruiser is full time 4x4. There is a difference, I’d try and explain it to you but the engineers would throw a sh!t fit for me not using all of the correct terminology in the exact correct way, so you’ll have to Google it.

Your Subaru is lower to the ground so it’s center of gravity is lower and it will handle better in the snow because of that.

The stability control uses the brakes to try and prevent a skid, it does not work, all you get is beeping and flashing warning lighs on the dash. You’re skidding because you lost traction, using the brakes to try and gain traction does not work. You’re not missing anything.

Doesn't VSC also attenuate your engine's RPMs to try to reduce torque to wheels?

 

[SmoothLC]

Hokie lax nailed it.

This from a 20yr ski patroller/Alta refugee (did I say 600" avg yearly snowfall). Always be in lo prior to the need. Anticipation/fear is your friend.

Temporary thread hijack: Love me some Alta . . . Carry on.

 

[J1000]

Pretty safe bet to do the opposite of what Spike555 says.

 

[MuseChaser]

I love snow, and have been living and driving in it for four decades. If this discussion was about driving technique for RWD manual transmission cars in snow, I'd have much more to offer. Contrary to what a lot of folks beloeve or are told, RWD is much more controllable than FWD in snow and ice. Yes, you lose drive traction more easily, but YOU DON'T SIMULTANEOUSLY LOSE STEERING ability like you do w/FWD. Skids are easily predictable and correctable. To be honest, I feel like I have more control in my little light Scion FR-S w/ good winter tires than I ever have in any of the AWD (MB ML430 and ML500) or 4WD ('93 Range Rover County LWB and current LX470) vehicles we've owned. The SUVs/trucks, of course, win the visibility, survivability, and "git yerself unstuck" discussions, but in terms of predictable response to bad conditions and subsequent driver input, they still surprise me at times. More than willing to admit that it's my relative lack of experience w/ 4wd compared to RWD over my lifetime.
The biggies for any winter driving, regardless of drivetrain, are, of course...
1. Drive slower, and keep the gaps wider between you and other cars.
2. No sudden control inputs... braking, steering, and accelerating. That`s why, as others have stated, downshifting an AT vehicle can cause trouble if you're on slippery roads. Light taps on the brakes instead. Driving in a lower gear isn't necessarily a problem, it's the lurchy change TO that gear. Having sais that, lower gears provide more torque, which can mean greater chance of losing traction when accelerating. In MT cars, I upshift sooner than I do on dry roads for that reason.
3. Putting any vehicle in neutral will not help braking; it will remove the innate drag of the engine (assuming, of course, you have your foot off the gas pedal), and will also remove your ability to accelerate if you find you need to. Unless you are stopped (or almost stopped w/ MT), you should not be in neutral for safety reasons.

I could offer all kinds of advice specific to handling RWD cars in snow, but who cares here. However, I'd love to hear some tips re/ specific response to conditions in 4wd. The discussion surrounding CDL seems inconclusive. I'm assuming 4Lo might be useful when trying to negotiate a descent, but otherwise the increased torque would seem to be a detriment and not an asset on slippery roads. Response to skids/loss of traction? I usually just ease off the gas until control returns and steer into skids, but that doesn't always feel as "positive" asmit does in RWD. Would love some coaching from seriously experienced 4wd snow-dwellers.

And... the one great truth that too many idiots ignore. Big, heavy 4wd vehicles don't stop any faster than 2wd vehicles...they just go faster. I can't tell you the number of times I've driven past AWD/4WD vehicles in the ditch after they've roared by little ol' me in my econosports car. Drive slow enough so you can stop in an emergency situation, regardless of what you drive.