80 in ice & snow + question re CDL

[lovetoski]

I've been driving ice/snow for many years in lots of different vehicles, with and w/out snow tires, studs, modern ice tires, chains, rear wheel drive, front wheel drive, 4W, etc. My two cruisers do well in the mountains in winter as you would expect. However, it wasn't until recently driving around town (hilly Seattle) that I realized how competent the 80 really is. We've had some wicked weather, with more "snow days" for the kids than I can ever remember. Driving the 80 has been totally uneventful. Boring even. So many vehicles spun out, in the ditch, stuck, sliding, wrecked, or parked. The 80 just motors along. Amazing.

Now to my question...when driving on the highway in ice/snowy conditions, does adding the CDL make the truck more stable at higher speed? On my 60, 4H feels like it wants to stay straighter in loose snow on the highway (plowed, but not recently). I wonder if adding the CDL switch would make the 80 feel more stable? It's not a lot of $, so I can add and find out for myself, but wonder if anybody here has some personal experience?

 

[RedmondCruiser]

I have had a lot of fun with the WA snow also. There has been a lot of recent debate on CDL use in the snow. Check out search for the details.

I personally use the CDL switch (well actually a hacked hazard light switch) on hill assents in the snow to make sure that power is evenly spread between front and rear. I don't think I would want to use it at speeds over 15 in the snow.

 

[eldgenb]

The CDL will not make it more stable on the snow at high speeds, it takes away the ability for the transfer case to compensate for individual wheel spin and in corners will make you more likely to lose traction. IMO

 

[Ronald_Type-R]

I usually lock the CDL when the roads are slippery/icy..Makes a huge difference on icy hills and things like that..And as for using it on higher speed on slippery roads, I do feel that the car is more stable when using the CDL...At times I found that when I turn off the CDL when driving on slippery roads, I can actually feel my rear end trying to break loose immediately..Nothing too too bad, but I can definitely feel the difference..

Just my personal experience though

Ronald

 

[haffi]

CDL

I use the CDL when both driving in snow and gravel roads. My cruser becomes much more stable.

I feel a graet difference on high speed (80 km+) driving on gravel roads, the car is like glued to the road with the CDL engaged.

 

[SUMOTOY]

I've been driving ice/snow for many years in lots of different vehicles, with and w/out snow tires, studs, modern ice tires, chains, rear wheel drive, front wheel drive, 4W, etc. My two cruisers do well in the mountains in winter as you would expect. However, it wasn't until recently driving around town (hilly Seattle) that I realized how competent the 80 really is. We've had some wicked weather, with more "snow days" for the kids than I can ever remember. Driving the 80 has been totally uneventful. Boring even. So many vehicles spun out, in the ditch, stuck, sliding, wrecked, or parked. The 80 just motors along. Amazing.

Now to my question...when driving on the highway in ice/snowy conditions, does adding the CDL make the truck more stable at higher speed? On my 60, 4H feels like it wants to stay straighter in loose snow on the highway (plowed, but not recently). I wonder if adding the CDL switch would make the 80 feel more stable? It's not a lot of $, so I can add and find out for myself, but wonder if anybody here has some personal experience?

There are quite a few threads not too many pages back on this issue. IME/O, the CDL on mode can be used anytime you feel it's more comfortable than CDL-off. I use mine quite regularly in daily driving.

At some point, I'll be bringing back some of the rather intense discussions regarding CDL use for daily driving. I dug through some of my files and found an SAE reference with a really good brake test with various diff locks. Open, center locked, center and rear locked, mixed mu braking (.8R, .25L) VS steering ability (non abs mode).

The results might upset the apple cart, but CDL on has the best steering ability on mixed mu under braking.

Back to your post, I personally advocate that folks understand when to drive with CDL on, it can be the best effective traction strategy of given road conditions. The reason the vehicle 'wants' to return to center is that a center diff lock resists axle speed differentiation, which is lowest with all four wheels straight.

ST

 

[PDoyle]

I use the CDL when the main roads are snowy and I'm cruising at about 55 mph.
It feels like a tank. Better when driving straight down the highway IMO.

 

[hill]

so to clarify things.... when is the right time to have CDL on.... and when is the inncorrect time to have CDL on....???

all these CDL posts seem to cloud around the right/wrong situations to have CDL on/off

 

[SUMOTOY]

so to clarify things.... when is the right time to have CDL on.... and when is the inncorrect time to have CDL on....???

all these CDL posts seem to cloud around the right/wrong situations to have CDL on/off

I think if you make tight turns, you want the CDL off - I got caught yesterday for the first time at a gas station - 3point turn to move the truck 5 feet over....

That said, the question is better addressed with when is the right time to have it off? When you want ABS functioning, when you are doing tight turns, and when you have concerns regarding axle binding.

I'm going to put some more interesting SAE studies up over the next few weeks. I'll start another thread on steering vs mixed mu in a few moments.

Stay tuned, it gets hairy here, not in the 80....

ST

 

[hill]

so your saying ...... its better to have the CDL on (ABS OFF) for the majority of driving?? or just winter driving??

obviously turning is impacted... i want to know whether its safer to drive snowy/ice highways with the CDL engaged (no abs) on not engaged (ABS on)

 

[Jeremiaheaster]

I too live in Seattle and had a lot of fun driving the 80 around. After a few tests I am certain that I want to install the CDL switch. Don't get me wrong the thing holds traction beautifully but without the CDL locked I felt that the 80 has a tendancy to spin out if given to much gas around a corner. The rear wants to break traction. However when in low (CDL locked) I can really punch it from a stop around a corner and the whole rig tracks beautifully. I want that traction without being stuck in low gear.

 

[jditom]

I use it at low speeds only especially when going up hill in snow. Never at high speed or down hill as it turns off abs which I have gotten use to.

 

[Grench]

At some point, I'll be bringing back some of the rather intense discussions regarding CDL use for daily driving. I dug through some of my files and found an SAE reference with a really good brake test with various diff locks. Open, center locked, center and rear locked, mixed mu braking (.8R, .25L) VS steering ability (non abs mode).

The results might upset the apple cart, but CDL on has the best steering ability on mixed mu under braking.

When ABS is left out of the comparrison.

 

[Walking Eagle]

so to clarify things.... when is the right time to have CDL on.... and when is the inncorrect time to have CDL on....???

all these CDL posts seem to cloud around the right/wrong situations to have CDL on/off

You're not going to get a difinitive answer - only opinions. I run CDL off on the hwy in ice and snow. Steers much better. CDL locked makes it want to go straight, and only straight. The whole reason you're not supposed to run CDL on dry pavement is it won't allow the wheels to slip when turning right? Well, if you run it in the snow / ice and turn, the CDL is going to make the tires slip. Your tire only has so much traction that can be used for stopping accelerating and turning. If you're forcing them to slip some just to keep the drivetrain from binding, you're loosing some of that traction that could be used for turning, stopping and accelerating. Unless you're spinning tires easily from accelerating, I don't see any need to hit the CDL button. And if you are in slippery enough conditions to use the CDL, you shouldn't be running at highway speeds.

It's the same type of deal as running a locker in the rear of a RWD car. If one wheel is on dry and one on wet, it's going to want to spin the car. Only now you're doing that front to back. Open diff you may not move at all, as the tire on ice spins wildly and the one on dry pavement just sits, but you'll stay straight.

So, with that logic, my oppinion is CDL off if the hwy is good enough you're traveling more than 35-40mph. If there is 2ft of snow on the road and you're making your own trail, hit the CDL.

The one thing alot of people forget, and you see plenty of them in the ditch with their 4wd trucks, is 4wd (CDL locked) is only going to help you get up to speed quicker. It does not allow you to brake better - you still have the same contact patch. It does not allow you to turn better - same contact patch minus the scrubbing from turning. It get's you going faster quicker, and often this provides a false sense of security, and you drive too fast, and you end up in the ditch or like the idiot I almost hit in the Escalade yesterday, in the middle of an intersection.

 

[SUMOTOY]

You're not going to get a difinitive answer - only opinions. I run CDL off on the hwy in ice and snow. Steers much better. CDL locked makes it want to go straight, and only straight. The whole reason you're not supposed to run CDL on dry pavement is it won't allow the wheels to slip when turning right? Well, if you run it in the snow / ice and turn, the CDL is going to make the tires slip. Your tire only has so much traction that can be used for stopping accelerating and turning. If you're forcing them to slip some just to keep the drivetrain from binding, you're loosing some of that traction that could be used for turning, stopping and accelerating. Unless you're spinning tires easily from accelerating, I don't see any need to hit the CDL button. And if you are in slippery enough conditions to use the CDL, you shouldn't be running at highway speeds.

I don't agree with this assessment. Back up to the axles. If you turn, the torque allocation goes to the rear, up to wheel spin, so forcing tire slip isn't necessarily going to cause loss of steering. In fact, it allows more steering up to wheel spin.

It's the same type of deal as running a locker in the rear of a RWD car. If one wheel is on dry and one on wet, it's going to want to spin the car. Only now you're doing that front to back. Open diff you may not move at all, as the tire on ice spins wildly and the one on dry pavement just sits, but you'll stay straight.

The dynamics of differentials and vehicle dynamics change when you compare front, rear and center.

The one thing alot of people forget, and you see plenty of them in the ditch with their 4wd trucks, is 4wd (CDL locked) is only going to help you get up to speed quicker. It does not allow you to brake better - you still have the same contact patch.

Not true, see Ideal Brake Force Distribution test.

It does not allow you to turn better - same contact patch minus the scrubbing from turning.

Not true, see Split mu chart, CDL steers better than unlocked.

It get's you going faster quicker, and often this provides a false sense of security, and you drive too fast, and you end up in the ditch or like the idiot I almost hit in the Escalade yesterday, in the middle of an intersection.

That *can* happen, it's not inherent to locking a center differential.

ST

 

[SUMOTOY]

When ABS is left out of the comparrison.

Actually, the comparison chart works really well even if you want to make the theoretical ideal 'assumption' that no steering correction happens with ABS on mixed mu. ABS is just not a significant variable.

ST

 

[Jeremiaheaster]

Unless you're spinning tires easily from accelerating, I don't see any need to hit the CDL button. And if you are in slippery enough conditions to use the CDL, you shouldn't be running at highway speeds.

OK so basically it sounds like driving with a lot of excellerating or cornering (around town) might be a good time to throw on the CDL. And driving at higher speeds on the highway, go without. Makes sense to me. What do you think SumoToy?

All I know is that during slippery conditions driving in 4lo, which is the only way I can lock my CDL right now, gives me WAY more stability and control than in normal drive, and I think the benefit I am feeling is coming from having the CDL locked and not from the lower gearing.

 

[puddles]

Interesting, I am located in Saskatchewan, Canada, and I can say that we get lots of snow and ice, and I am amazed at how well the landcruiser does in the snow. I have only had it since July, but I also have an 07 GMC 2500HD Duramax 4X4 and it does not compare in this respect. I need to lock it in 4X4 to see similar traction and once I do that my turning ability is greatly impared. As far as I am concerned unless you are travelling at low speeds in extrememly heavy snow I would not bother locking up the CDL, with good tires the the all time 4wd and the extra manuverabilty of not locking the CDL I would not bother. Just my experience.

 

[Grench]

Actually, the comparison chart works really well even if you want to make the theoretical ideal 'assumption' that no steering correction happens with ABS on mixed mu. ABS is just not a significant variable.

ST

Assume the driver panics and slams the brake to the floor. All models except ABS fail instantly.

Every single example you have given ignores wheel lockup and it's inherent loss of control. With the CDL on, wheel lockup occurs later than it does in a non-ABS no-CDL vehicle. However, when it does occur in the CDL example it is more sudden as all 4 wheels slide at once. Without the CDL the typical vehicle will lock the rear wheels first, giving the driver time to correct the pressure before the front end slides.

A locked wheel has no directional stability. A vehicle with all 4 wheels locked (CDL or non-ABS) will move/slide/crash in the direction of it's greatest momentum.

 

[KliersLC]

STOP!


Driving with the CDL on is just like putting a normal 4wd vehicle in 4Hi.


NO Difference.

FWIW, I run the 80 unlocked all over the countryside in the snow and ice, and I run my pickup in 4Hi, Either is fine in snow and ice.