Snowy Freeway Mountain Pass - VSC vs Center Diff Lock (1 Viewer)

[Qtonic]

I'm trying to better understand the 4WD options under various conditions.

Say you were in a snowstorm driving over a mountain pass, would you keep the hundy in normal mode or engage the center diff? As I understand it, locking the diff disables vsc. I'm interested in your thinking regarding the tradeoffs.

 

[RedHeadedStepChild]

Unless you are stuck and unable to move forward, Leave the CDL unlocked in the snow.
If the center diff is locked, you WILL have a tire slip in corners. All wheel drive is what you want in the snow, and it's what you have driving normally. Unless you want to go out and blow donuts, the traction control and VSC are your friend when it's getting hairy in a mountain pass.

 

[Qtonic]

Exactly what I needed to know. Thanks!

 

[Spike555]

I can tell you with personal experience that you want to use the center locking differential in the heavy snow. This sends equal power to both axles so you no longer get more power to one axle or the other.
This allows you to use the throttle to pull you out of a skid, this also prevent’s the rear from kicking out on you because it got more power than the front.

Your traction control stays on and stability control only shuts off if the t-case is in lo range. This is vehicle year dependent, but on my ‘04 this is how it works.

Use the CDL, you can drive at any speed with it locked too, just not on dry roads.

Where I live, we average 70” of snow per year. Where my wife is from the yearly average snow is 104” per year. So yeah...CDL locked for 160miles while driving 70mph on snow covered expressway on the way to grandma’s house for the holidays...

All of this being said, if you have crap tires, nothing will help you.

 

[Spike555]

Just two different typical winter days here in Michigan. Those telephone poles are about 25yds away. The road runs parallel to them.
The top picture is the expressway. Use the center diff lock. Just don’t drive stupid.

 

[krice118]

@Qtonic

I disagree with the first reply. For the 98-99 non ATRAC guys, the CDL is invaluable. CDL gives more control and quicker response. Of course these 100s can make it through anything, STOPPING in snow is the hard part - use your transmisson and be graceful when applying brakes

Btw in a 100 with bigger tires its hard to do donuts, you really gotta push it hard.

In snow i use the 2nd start

 

[RedHeadedStepChild]

I don't disagree that CDL provides greater FORWARD traction. But to make a corner, the front and rear tires follow different tracks and therefor it WILL cause tire slippage in corners is therefor less safe on curvy snow covered roads. On a generally straight road or road with gentle curves, you likely won't notice, but since the OP mentioned mountain roads, I assume he's dealing with tighter corners.
As @Spike555 said, good tires are key.

 

[Captndcoke]

@Qtonic

I disagree with the first reply. For the 98-99 non ATRAC guys, the CDL is invaluable. CDL gives more control and quicker response. Of course these 100s can make it through anything, STOPPING in snow is the hard part - use your transmisson and be graceful when applying brakes

Btw in a 100 with bigger tires its hard to do donuts, you really gotta push it hard.

In snow i use the 2nd start

Can you compare/provide info on how '00 LX does?

 

[krice118]

Can you compare/provide info on how '00 LX does?

I have a 98 LC so I can’t say with experience how an ATRAC truck would be but I would use the CDL and drive with caution given the conditions. In my experience the CDL gives much greater control.

Drive in a safe place that is snowy or muddy and try to get the LX loose with the CDL off and and then do the same with the CDL on. You have to feel it, experience is better than internet speculation

 

[MuseChaser]

.....experience is better than internet speculation

Blasphemy!

 

[uzj100]

Depends on what you are attempting to accomplish.

1. Safely get you and your family home in light snow, vsc only, no center diff lock, snow gets deeper and you need more traction, center diff locked and drive even slower.

2. Ken Block/Colin McRae world rally skills contest, lock center diff and get after it in all conditions. Passengers do get nervous but really lots of fun! ;<)

I use #2 when I have no cars around me and my wife is not in the car.

 

[LXMUTT]

From my understanding, when the CDL is disengaged (meaning all wheel drive) power is split between all 4 tires equally, but if one tire slips all the power would go to that tire until the traction control kicks in. When the CDL is engaged(true 4x4) power is split equally between the front and year (same thing that happens when you go from 2 to 4 wheel drive on another car) but some stability control settings turn off on some model years. on the slippage around corners, CDL does not lock the front and rear differentials which means they allow differentiating(one side spinning faster than the other side) around corners allowing minimal slippage, unless under power then there is a little understeer on tight turns. On a very slippery road (snow and ice) I engage the CDL because its now true 4x4 and power can always get at least 2 wheels all the time.

 

[uzj100]

Yes VSC is turned off when CDL is engaged.

 

[RedHeadedStepChild]

From my understanding, when the CDL is disengaged (meaning all wheel drive) power is split between all 4 tires equally, but if one tire slips all the power would go to that tire until the traction control kicks in. When the CDL is engaged(true 4x4) power is split equally between the front and year (same thing that happens when you go from 2 to 4 wheel drive on another car) but some stability control settings turn off on some model years. on the slippage around corners, CDL does not lock the front and rear differentials which means they allow differentiating(one side spinning faster than the other side) around corners allowing minimal slippage, unless under power then there is a little understeer on tight turns. On a very slippery road (snow and ice) I engage the CDL because its now true 4x4 and power can always get at least 2 wheels all the time.

This is true that left to right differential action is still in play, however, the center differential exists because there is a need to differentiate the rotational speed between front and rear as well. If there was no need for this, manufacturers would not add the complexity and the cost. You need to consider there are different traction issues in play here. For purely forward traction under power, CDL locked will offer superior performance. Aside from just being stuck, does anyone actually get into trouble with a lack of forward traction? I guess if you do, you're just doing it wrong. Where people get into trouble is the loss of lateral traction. As steering inputs increase, there is a greater rotational speed differential between the front and the rear. Since the vehicle is, for all intents and purposes, a rigid structure if the wheels need to turn at different rates, but are locked together, something must give (this is physics and not subject to opinion). That something will be traction of a tire. Once a tire has lost traction in a corner, it loses much of its ability to resist lateral loads this leaves only 1 tire available to keep a given end of the vehicle from sliding sideways.
Driving with the CDL on does feel more responsive because when you feed it the skinny pedal you have an additional tire pulling, but that feeling does not actually translate into better handling performance.

 

[RedHeadedStepChild]

Depends on what you are attempting to accomplish.

1. Safely get you and your family home in light snow, vsc only, no center diff lock, snow gets deeper and you need more traction, center diff locked and drive even slower.

2. Ken Block/Colin McRae world rally skills contest, lock center diff and get after it in all conditions. Passengers do get nervous but really lots of fun! ;<)

I use #2 when I have no cars around me and my wife is not in the car.

Now if you're on muddy grass in NC...

 

[Spike555]

Having the CDL engaged during a turn will not do anything unless you are trying to make a tight U-turn, only then will it effect steering/slipping sideways.
Normal driving you will have zero problems.
If the road is slippery I am assuming that you are smart enough to slow down so that you do not go sliding off into the ditch.
Mountain pass or state highway makes no difference, mountain pass is going to have guard rails, state highways not always.
The VSC is useless no mater what. The ATRAC is not bad. You have to spin the tires and keep spinning them for it to work.

When there is no one else around I like to have fun in the snow. I lock the CDL, throw it into a hard turn to kick out the back of the truck and hit the throttle, the front wheels grip and straighten you right out.
If they do not have traction then you’re going to keep going in a circle.
If you know what you are doing you can drive with the throttle, you don’t even need the brakes. I hate ABS in the snow because it increases stopping distance. You stop quicker by not locking up the wheels at all, brake until you feel the tires skid then back off the brake pedal just enough to let the wheels start rolling again and then keep that same amount of brake pressure. Skidding tires have zero traction. Traction is key. Traction is nothing without control.

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.

As far as driving in the snow experience, I’ve been driving since I was 14, i’m 46 and I have been a professional driver since I turned 20.

Snow tires will give you the best traction, the more expensive the tire the more traction you will get. Use the CDL. Take it slow. Don’t be a Richard. The only thing that will help you stop in snow is snow tires. Serious snow tires make the snow feel like rain. That is the amount of traction you get with GOOD snow tires.

And I’ve lived here in snow country my whole life. I am no expert. But I do know a few things about driving in the snow.

 

[RedHeadedStepChild]

Ok I'm out.

 

[RiverRatMatt]

This is true that left to right differential action is still in play, however, the center differential exists because there is a need to differentiate the rotational speed between front and rear as well. If there was no need for this, manufacturers would not add the complexity and the cost. You need to consider there are different traction issues in play here. For purely forward traction under power, CDL locked will offer superior performance. Aside from just being stuck, does anyone actually get into trouble with a lack of forward traction? I guess if you do, you're just doing it wrong. Where people get into trouble is the loss of lateral traction. As steering inputs increase, there is a greater rotational speed differential between the front and the rear. Since the vehicle is, for all intents and purposes, a rigid structure if the wheels need to turn at different rates, but are locked together, something must give (this is physics and not subject to opinion). That something will be traction of a tire. Once a tire has lost traction in a corner, it loses much of its ability to resist lateral loads this leaves only 1 tire available to keep a given end of the vehicle from sliding sideways.
Driving with the CDL on does feel more responsive because when you feed it the skinny pedal you have an additional tire pulling, but that feeling does not actually translate into better handling performance.

This, there's a reason companies like Subaru use dynamic AWD

 

[krice118]

Having the CDL engaged during a turn will not do anything unless you are trying to make a tight U-turn, only then will it effect steering/slipping sideways.
Normal driving you will have zero problems.

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.

I was thinking the same thing about the CDL.

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

As steering inputs increase, there is a greater rotational speed differential between the front and the rear. Since the vehicle is, for all intents and purposes, a rigid structure if the wheels need to turn at different rates, but are locked together, something must give (this is physics and not subject to opinion). That something will be traction of a tire. Once a tire has lost traction in a corner, it loses much of its ability to resist lateral loads this leaves only 1 tire available to keep a given end of the vehicle from sliding sideways.
Driving with the CDL on does feel more responsive because when you feed it the skinny pedal you have an additional tire pulling, but that feeling does not actually translate into better handling performance.

I think you are describing a Triple Locked rig ( Front diff locked, Rear Locked) Situation not just a CDL. CDL locked still allows the wheels to turn at different rates.

 

[RedHeadedStepChild]

I was thinking the same thing about the CDL.

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 think you are describing a Triple Locked rig ( Front diff locked, Rear Locked) Situation not just a CDL. CDL locked still allows the wheels to turn at different rates.

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.