Understeer in Snow with Limited Slip Differential

[Meeker]

Now that I'm well into winter with my 2018 XLT (SWB, HD Tow, 4x4) I've had a chance to compare to my 2006 Limited.

I'm convinced that the 2018 is more prone to understeer in the snow. I suspect 2 reasons:

- 2018 has the Primacy tires which are definitely underwhelming in the winter. I had upgraded the 2006 to Michelin AT/2 tires and they were great in winter.
- 2018 has the limited slip differential, whereas the 2006 had open diffs.

One day I played with the rear diff lock on a whim, and wow it was like somebody disconnected the steering wheel! Only wanted to go straight... definitely won't be using that in all but dire circumstances. This was on packed snow, not ice BTW.

I guess my point is, even if I change the tires, I'm still expecting a bit more understeer than the 2006. Anybody else notice this, or am I off track (see what I did there)?

 

[JExpedition07]

Now that I'm well into winter with my 2018 XLT (SWB, HD Tow, 4x4) I've had a chance to compare to my 2006 Limited.

I'm convinced that the 2018 is more prone to understeer in the snow. I suspect 2 reasons:

- 2018 has the Primacy tires which are definitely underwhelming in the winter. I had upgraded the 2006 to Michelin AT/2 tires and they were great in winter.
- 2018 has the limited slip differential, whereas the 2006 had open diffs.

One day I played with the rear diff lock on a whim, and wow it was like somebody disconnected the steering wheel! Only wanted to go straight... definitely won't be using that in all but dire circumstances. This was on packed snow, not ice BTW.

I guess my point is, even if I change the tires, I'm still expecting a bit more understeer than the 2006. Anybody else notice this, or am I off track (see what I did there)?

Lockers and snow don’t mix lol. You are correct with that engaged the truck will want to go straight because when turning one wheel needs to spin faster than the other in rear as well as front. Not allowing this will cause slippage and fishtailing. If your 2006 had 4WD and AdvanceTrac it had an “off-road” program that mimics a limited slip(s) using the ABS system....this programming was availabe from 05-14’ Expeditions equipped with 4x4 and AdvanceTrac. In 05-06 you could choose either the AdvanceTrac and braking bias software or Limited Slip on a 4x4, not both. The limited slip was removed from 2007-2015 vehicles. It made a return in 2016....this obviously meant software changes. Different trucks with different programming/ wheels/ steering.

The understeer is likely a combo the tires and epas, your 06’ had hydraulic power steering. Limited slip may be part but not sure.

 

[Meeker]

Lockers and snow don’t mix lol. You are correct with that engaged the truck will want to go straight because when turning one wheel needs to spin faster than the other in rear as well as front. Not allowing this will cause slippage and fishtailing. If your 2006 had 4WD and AdvanceTrac it had an “off-road” program that mimics a limited slip(s) using the ABS system....this programming was availabe from 05-14’ Expeditions equipped with 4x4 and AdvanceTrac. In 05-06 you could choose either the AdvanceTrac and braking bias software or Limited Slip on a 4x4, not both. The limited slip was removed from 2007-2015 vehicles. It made a return in 2016....this obviously meant software changes. Different trucks with different programming/ wheels/ steering.

The understeer is likely a combo the tires and epas, your 06’ had hydraulic power steering. Limited slip may be part but not sure.

Not sure what you mean by epas - do you mean electric power steering? Didn't think of that.

Yes my 06 had 4x4/AdvanceTrac. Better on-road, but lacked a bit off-road. I was parked in a narrow ditch in the mountains while canoeing, and while turning out I had the 06 suspended on the front right and rear left tires and the others in the air. The brakes made a hell of a noise but it got me going!

But back to this question - I thought I saw that this LSD is not like most of them in that it uses electronically controlled clutches. Would this mean that there would be no "limited slip" until wheel spin, so that going around a corner would be the same as an open diff? Or do they keep some clutch pressure at all times to ensure some power going to both wheels no matter what? Or maybe I'm mistaken about the diff.

 

[scottdm]

I can also confirm the understeer behavior in snow even with new snow tires. I was first in line at a traffic light for a left turn across a 4 lane and there was maybe 2" of slushy snow on the road. I'm used to giving it the beans in the snow with my old S550 4-Matic with snow tires and it would just hook up and go. The Expedition with snow tires hooked up fine in 4-Auto, but as I started to turn I just kept plowing forward. Not good! I had to completely let off the gas before it finally started to turn. Wasn't impressive for sure!

 

[JExpedition07]

Not sure what you mean by epas - do you mean electric power steering? Didn't think of that.

Yes my 06 had 4x4/AdvanceTrac. Better on-road, but lacked a bit off-road. I was parked in a narrow ditch in the mountains while canoeing, and while turning out I had the 06 suspended on the front right and rear left tires and the others in the air. The brakes made a hell of a noise but it got me going!

But back to this question - I thought I saw that this LSD is not like most of them in that it uses electronically controlled clutches. Would this mean that there would be no "limited slip" until wheel spin, so that going around a corner would be the same as an open diff? Or do they keep some clutch pressure at all times to ensure some power going to both wheels no matter what? Or maybe I'm mistaken about the diff.

Yep epas is electric steering...I always found the off road program on my 07’ to be pretty helpful as well. Instead of the previous rear mechanical lsd you have help on all 4 wheels.

You are likely correct regarding your limited slip in your 18’, it is an eLSD...not the same as the older mechanical versions. The issue with the previous mechanical ones was the maintenance and wear factor....that and they couldn’t communicate with the computer. Regarding your question, it most likely acts as an open diff around turns and normal conditions...engaging when it senses slippage. I don’t think your eLSD is causing the understeer unless you are juicing it around corners.

 

[rumline]

Cars are generally designed to understeer when pushed too far so most likely it's the traction control / epsa telling you to dial it down a notch. I agree that the Expy does it more than I'm used to however this isn't exactly a performance-oriented vehicle.

 

[TobyU]

Same with old muscle cars doing burnouts.
With open rear...(one wheel wonders) you could drive straight down the road with one tire smoking until you let off. With a limited slip/ locker, you would have to work to keep in lane as back end swayed back and forth or wanted to fishtail out often.

But I GOT TO HAVE limited slip!!!

 

[benyl]

It isn’t the limited slip. It’s the setup from the factory.

With the additional power it has over the 06, they’ve set it up to be prone to understeer. Understeer is safer than neutral.

I’m sure you could work with an alignment shop to dial it out. Playing with tire pressures can also help.


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[scottdm]

If I have a chance, I’ll also experiment with the different drive modes to see if it makes any difference in how the traction control responds. I had just gotten off the highway and was in Eco mode with 4 auto engaged when I experienced the understeer.

 

[dlcorbett]

Snow mode works very well. I dont think mines had any made any unpredictable moves in snow mode.