Kudos to Limited Slip

[BrianW]

Originally Posted by deserteagle56

My rule of thumb in bad road conditions:

Stay home. Feed the fire and smile as I look out the window and sip my favorite hot beverage!

I leave my 19 foot long van at home and drive my Subaru with XIce snow/ice tires on it. It goes great, and more importantly, stops great too on the slick stuff.

[Jsweezy]

Originally Posted by arctictraveller

I'm definitely in the "hate chains" school of thought, but I do carry them just in case. Still, I've only used them perhaps 3 times in my life, and each case I was forced by law to install them. I do think they are good to have when traveling in remote backcountry areas in winter though. As for limited slip, I installed it on my front axle too, in addition to the stock one in the rear. When I bought the van, I didn't know it wasn't working in the rear until I installed new gears and discovered the clutches were all burned out. Now, everything is fresh in both ends and I think adding it in the front was the best compromise between hard core off road and limited slips ability to be used on the street.

That's a good idea, I may look into doing that...

[Otter]

Originally Posted by Flux

My rule of thumb in bad road conditions:

Never drive faster than you are willing to crash

Flux, this is my full time rule. Having been in several accidents caused by others, I have a hypersensitivity to the dangers of just being in a car, minding your own business. Like the time that unexpected someone ran a stoplight and got t-boned by me. Glad I was doing the 45 mph speed limit, or we both might not be around to tell about it.

There are few more sickening feelings, though, than going slowly and feeling your vehicle slide incomprehensibly off in the direction of that telephone pole. I've been criticized many times in my life for driving "so carefully", but I'd rather slide into that pole at 10 mph than 40. Dents can be fixed, and a lot cheaper than bones, right?

Question for MountainBikeRoamer: I'm trying to envision the scenario you're suggesting about ice and lsd. Let's say I'm driving on solid ice -slowly, cause I would- are you saying that, if my tires lose traction with the ice/road, the rear axle might swing wildly more than it would with no lsd? I don't understand the why of that. Or are you talking about driving on a road with patches of ice, where one wheel could be gripping solid road? And, what if we add studs to that picture? Studs give me more grip on the ice, that I know. Just trying to figure out my best options down the road.

[MountainBikeRoamer]

Originally Posted by Otter

Question for MountainBikeRoamer: I'm trying to envision the scenario you're suggesting about ice and lsd. Let's say I'm driving on solid ice -slowly, cause I would- are you saying that, if my tires lose traction with the ice/road, the rear axle might swing wildly more than it would with no lsd? I don't understand the why of that. Or are you talking about driving on a road with patches of ice, where one wheel could be gripping solid road? And, what if we add studs to that picture? Studs give me more grip on the ice, that I know. Just trying to figure out my best options down the road.

Think of it this way:
The reason your van (or any vehicle with wheels) is "controllable," at any point in time (as in, you can steer it....and it drives forward in a straight line, without "spinning out" or driving sideways.....) is because:

It's "easier" for your wheels to continue *rolling* forward, in a straight line than it is for them to slide sideways. It's far less friction for the wheels to keep going straight. And when you steer the front wheels in a new direction, it's the lateral (sideways) force of friction on the tires' contact surface that "pushes" the car to go in the new direction you choose. Without that all-important lateral force of friction, your van would keep on going straight, no matter what angle you steered your tires in.

In short --- the magic of a wheel is that it prefers to move forward in the same direction that it rolls. Friction is what makes this happen, however! In a world without friction...a wheel would just as happily slide sideways as it would forward. And without friction, it wouldn't want to roll, it would just slide....even when going "forward."

So on a driving surface with friction (dry pavement...or even dirt.....or mud....or packed snow.....but not ice.....), rear tires are always (since they're always aimed straight forward) acting as "rudders" on the rear of your vehicle, keeping the rear tracking straight forward and following the lead of the front tires which are choosing the direction for the van to follow.

BUT NOW INTRODUCE ICE TO A LIMITED-SLIP DIFF.
And perhaps you tap your brakes....or go around a corner and perhaps the rear LSD senses wheel slippage and kicks in with a jolt, momentarily breaking both wheels loose (as a pair, since the diff is now locked) from gripping the road surface. Suddenly....the rear (and front) tires have a choice to make: What's easier? Continuing to roll forward, in the direction the driver is expecting (and requiring in order to maintain control).....or to just slide sideways?

The minute that *both* tires lose traction in the rear....YOU'VE COMPLETELY LOST YOUR RUDDER.

At that point, once a spin has begun......the only way that the rear tires are going to *anchor* the rear and stop the spin, or stop the van from sliding sideways in any direction it feels like, is if both tires "catch" on the ground again, and start to *roll* at the same speed as the ground. And with a limited-slip, or especially a locker rear axle, once a slide has begun, it's nigh impossible on ice for *both wheels* to grab hold of the ground again and regain control.

With an open rear diff, if one tire "breaks traction," you've still got the other tire acting as a "rudder," keeping the van tracking forward. And the wheel that temporarily broke traction stands its best chance of "hooking back up" once it stops spinning, since its still aimed forward (and not sliding sideways.)

-------------------------------------------------

I'm not sure how the LSD in your van works --- (is it electronic? Or torque-sensing mechanical? Or is it simply a friction-pack in the diff that provides some resistance to spinning like an open diff?) --- but each type will behave differently when a 2WD rear-drive vehicle suddenly encounters ice -- especially in a turn, when the inside wheel wants to track a little slower than the outside wheel (most common time for a rear LSD or locker to break loose.) If yours kicks in with a sharp jolt, that could be all that required (while in a turn especially) to break both wheels loose and send you spinning.

If you're getting lost in my explanation....this thread from back in 2003 on the offroad.com forum does a great job of discussing this as well.

Lockers vs Limited Slip in Snow and Ice - Off-Road Forums & Discussion Groups

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In any event ---
As someone else already mentioned here today --- let's all be careful out there!

Good to make it back home to where the warm fire (and hot beverages!) are waiting.

Cheers!!!!

[Otter]

I'm not sure how my lsd works, but it's stock from a 2013 E350, so whatever that is...

I've felt the lsd kick in several times in different situations, including pulling out from gravel and yesterday's ice scenario. It doesn't kick in with a jolt. There's a "whirring" sound (sensation?) followed by a quiet stabilizing moment, when you've clearly got traction. Prior to installing this axle, I was none too happy with the open diff's tendency to just keep spinning. I often pull my trailer in deep gravel and found myself getting frustrated with it. Of course, the addition of 4WD will eliminate most of that problem altogether.

After your explanation and reading the one on off-road forum and others, I'm thinking the best plan with lsd and ice is to not lose traction in the first place. As in, I see studs in my future.

[carringb]

MTBRoamer is correct - lockers are actually "destabilizing" on ice. So is limited slip, but not as bad because it engages less abruptly (and lessens grip as soon as you let off the throttle). But sill better than not moving at all!

I ended up chaining up last night. I definitely didn't want to, but the signs were up, and I had already gotten stopped behind other trucks that could not get going, and I didn't want to risk a chains ticket.

Sure glad I did! When I got to Tombstone pass it was about 8" of buttery mashed potatoes. It was like driving in greasy mud! Even with chains and good limited slip, I had to just throttle through some deep spots, which of course made the rear end slide towards the ditch. So it was a game of throttle in to get some speed, then throttle off to get things pointed straight. For about 15 minutes. I thing all the plows were re-directed to Santiam pass because of all the stuck big-rigs. It was my least pleasant drive over the passes yet. The freezing rain actually didn't treat me as bad as the mashed potatoes did!

[dhally]

I've had some experience sliding around with LSD vs. open. The Ford LSD has friction clutches so there's is always some resistance to different wheel speeds. This can be a factor under super slippery conditions. The LSD drags enough to cause one rear tire to slip in a corner. For instance, once I was going about 30 mph and abruptly lifted the throttle. The rear end broke loose. I slipped the tranny into neutral and it straightened out.

A bigger issue is when the lsd does engage, like going around a flat uphill corner. Give it gas to climb, one tire slips and the LSD locks up. It will immediately kick out the tail. Depending on the road angle, it could kick to the inside of tyhe corner (downhill). Lift off too suddenly and it gets worse.

I think the LSD is great, but its main benefit is climbing straight up a hill. It can help on the open road, but it takes more attention and skill to stay stable. I wish my van had RSC...

[SteelheadJones]

Originally Posted by arctictraveller

As for limited slip, I installed it on my front axle too...

Arctic do you have details on this? What axle, what year, what limited slip, part #'s, etc?

[dhally]

Originally Posted by Otter

I'm not sure how my lsd works, but it's stock from a 2013 E350, so whatever that is...

I've felt the lsd kick in several times in different situations, including pulling out from gravel and yesterday's ice scenario. It doesn't kick in with a jolt. There's a "whirring" sound (sensation?) followed by a quiet stabilizing moment, when you've clearly got traction. Prior to installing this axle, I was none too happy with the open diff's tendency to just keep spinning. I often pull my trailer in deep gravel and found myself getting frustrated with it. Of course, the addition of 4WD will eliminate most of that problem altogether.

After your explanation and reading the one on off-road forum and others, I'm thinking the best plan with lsd and ice is to not lose traction in the first place. As in, I see studs in my future.

Your van must have RSC. I bet the whirring noise is the RSC working (pulsating the brakes). I'm not sure how the LSD comes into play, since the RSC brakes the spinning wheel before the LSD can engage? The RSC should stop the van from going sideways.

My van only has traction control not RSc. I turn off traction control to bring the LSD into play for deep snow etc.

[Otter]

Originally Posted by dhally

I've had some experience sliding around with LSD vs. open... I think the LSD is great, but its main benefit is climbing straight up a hill. It can help on the open road, but it takes more attention and skill to stay stable. I wish my van had RSC...

Thanks for the description. Mine has both TSC and lsd. I's a trip trying to figure out what's doing what and when. I have yet to figure out if it has RSC too.

@carringb: Ugh! I went through those passes a few years back in a complete whiteout. I couldn't see anything but was getting hypnotized by the snow blowing straight at the windshield. I was ferrying a partying group of ski patrollers to our training exercise down there. Everybody was having a great time laughing and telling jokes except me and my white knuckles. Shoulda pulled over but couldn't see enough to do that. Finally came down on the other side where that restaurant is. It all turned out okay, but I was never quite the same after that. And yeah, chains were on good and tight.