4-Wheel Drive or Snow Tires?

[Monique]

When you do ice rink tests, winter tires win, but people don’t drive on ice rinks and so you’re going to get the variable of the vehicle, too.

In my experience, the front range and I-70 rarely have much ice - more likely to deal with snow. Either way, that first winter precipitation is gnarly as drivers get their bearings, and likely haven't swapped tires if they're going to.

 

[mister moose]

Running snows until "worn out" is foolish.

I run worn snows down to the wear bars in the summer. Might as well use em up.

Snow tires help you stop, turn, and go. AWD/4WD help you go. Having lived *in* the CO mountains for the last 3 winters (and having the driveway voted "worst" by the guys who plow most of the county), with a front wheel drive car and four non studded snow tires... I can tell you that its the tires that matter,

4WD helps you steer and brake as well.

Static friction is greater than kinetic friction. That means you have more traction when the tire isn't slipping, and once slipped, it's harder to regain. 4WD keeps at least 1 wheel in the front and one wheel in the back turning. If the excess torque (above slippage torque) is minimized by feathering braking or the gas pedal, the skid can be managed/avoided. With good feathering all 4 wheels keep contact by not driving the differential into differentiating.

Example:
2WD brake in a straight line, apply brake, all 4 wheels skid. Driven wheels slow down and non-driven wheels lock up. When you get off the brake the non driven wheels may still skid as there is insufficient traction to spin the wheels back up to vehicle speed.
4WD: brake in a straight line, apply brake, all 4 wheels skid, however they are still spinning just below vehicle speed. The direct connection to the engine keeps the wheels rotating, they all can't lock up unless you jam the brakes so hard you stall the engine. (Stick shift) If you get off the brake you can re-establish tire/snow contact and regain control. An automatic compromises this effect as you don't have a direct hard connection from the wheels to the engine..

In turns, even though the front wheels may slip, driven front wheels will still pull you into the turn if you feather the gas. In 4wd the rears provide added boost to keep the vehicle moving.

Note that I'm talking snow, not black ice. Real glazed ice on the road generally means you're going for Mr Toad's wild ride. (yeah, yeah, Blizzaks) Worse yet is wet ice - no control.

With the advent of ABS braking control has been taken away from the driver in a skid. This is undesirable as when one wheel slips, ABS kicks in even if the other 3 have good traction still. ABS usually increases your stopping distance at the expense of mandated pulsed braking to salvage steering for a panicked driver.

So in snow,

Stick > automatic
4WD > AWD
AWD > FWD
FWD > RWD
No ABS > ABS (for a skilled driver)
Snow tires > All season tires
Fresh tread > worn tread
Subtle changes > Texas stomp

This leaves a zillion combinations where arguments can be had over which is better. That said, I'll take my 4WD snow tire shod, stick shift, high clearance truck over almost anything else in snow. I've been in snow deep enough to roll waves of snow over the hood.

For inexperience snow drivers, go out and practice. Turn big slow donuts in a parking lot in the snow, building speed until you feel the wheels start to slip. Play with holding that speed and managing the speed and turn at the slip threshold. Try some skidded turns and regain steering control by widening the turn and easing off the gas. Get up to 25mph and then experiment with braking, applying brakes slowly increasing brake pressure until you feel the wheels slip. Ease off just a little until you feel the wheels re-engage. Find the maximum stopping force you can apply. Learn to feather, ie small adjustments constantly adjusting to suit the response. When going up a hill in a snowstorm, try goosing the gas until the tires slip and then ease off. That's your maximum torque available to get up the hill, and you might need it at the steepest part. Momentum is your friend up hills and your enemy down hills.

Small losses of traction is information. Massive loss of traction and massive corrections lead to loss of control. Leave huge space between you and the next car.

 

[scott43]

Wow there are a lot of Formula 1 drivers here while they're heading for the ditch at 50mph...

 

[Monique]

I run worn snows down to the wear bars in the summer. Might as well use em up.

Me, too. Until they get so LOUD I can't bear it.

Stick > automatic

I do miss the control of a stick in snow. That's the only time, though, actually.

 

[James]

If you really want to split the baby, you could go with say a Nokian All Weather tire. The WR G3 Suv. You'll pay a handling penalty in summer. That would really be for the pseudo? Awd version of the Highlander.
Really, if you're moving to snow country you ought to get snow tires for the winter. Esp with FWD.
Then go to some parking lots and practice.

 

[SShore]

I have a pair of Nokian All Weather/All Terrain on my RAM 1500. Quite frankly, they are a compromise on both ends and IMHO, not a good one. I went and bought real snow tires after the first snow of the season because their deep snow traction was not good and the summer wear on them is terrible. I lost more than half my tread in less than 20K driving. I'll stick with the Blizzaks (only real truck snow tires I could find here) and will be switching to another Summer AT tire after this summer.

 

[nay]

In my experience, the front range and I-70 rarely have much ice - more likely to deal with snow. Either way, that first winter precipitation is gnarly as drivers get their bearings, and likely haven't swapped tires if they're going to.

We’ve had way more ice in recent years as CDOT has taken to chemical melting, and there were some nasty black ice events on I-25 this season. I always said the same thing, but ice in CO is becoming more prevalent.

Here’s some vids I took to demonstrate that it’s not just tires. These are polar opposite vehicles with the Land Cruiser on 37” off-road tires and the Quest minivan on studded snows. This is typical icing where I live when powder packs to ice. Not ice rink stuff.

This is trying to slide.


Here we see the superiority of the off-road tire in holding snow for snow on snow traction on top of the ice. The winter tire, which has design properties to pull water off of ice (that ice rink test) is ineffective in these cold conditions (it was about 2 degrees) - without studs it would have been unable to get up this 2-3 degree hill. The Cruiser is initially just in straight AWD - no locked center diff and zero slip. I lock it to show hammering the throttle and still staying in full control.


Here is passing in a deep and heavy consolidated snowplow bank. I ultimately have to lock all three differentials to avoid taking a run at speed, but with frame weight on consolidated snow this would completely defeat any AWD/snow tire/standard 4WD configuration. At the end, you can see how the tire holds and clears snow going in and out of slush and melt.


This is all a good example that the vehicle matters tremendously and all “off-road” tires are not the same. A 1995 Land Cruiser has a horrid ABS system and no other electronic traction control, but because of its weight distribution and mechanical lockers it easily outperforms modern traction control systems without a need for specialized winter tires.

 

[James]

I have a pair of Nokian All Weather/All Terrain on my RAM 1500. Quite frankly, they are a compromise on both ends and IMHO, not a good one. I went and bought real snow tires after the first snow of the season because their deep snow traction was not good and the summer wear on them is terrible. I lost more than half my tread in less than 20K driving. I'll stick with the Blizzaks (only real truck snow tires I could find here) and will be switching to another Summer AT tire after this summer.

They make those Nokians in a truck tire? What size did you get? My sense is that once you have a vehicle that big car tires don't survive well.

 

[Don in Morrison]

I tried to find the WR G3 for my Dodge Carryvan, but there were none to be found anywhere. I have them on my Chevy Cruz and I found their limit in a heavy storm on the Front Range in April. They gave up about 100 yards from my destination near Conifer. I did make it about 1/4 mile farther than a 4WD headed for the same place.

Always remember that the only thing 4WD is good for is getting stuck in a harder place to get out of. The SUV's you find upside-down in the snow on the side of the road were driven by people who didn't understand that.

 

[nay]

For me it is the MPG's. I already lost 12MPG going from the TDI to the Alltrack...I am not sure how much more I want to give up.

The rolling resistance of these newer tires is really low - gone are the days of getting traction just by soft compound, so I can’t imagine it’s anything major.

My points of reference are terrible for you, but I gained 1 mpg going to BFG ko2, and on 37” tires (and lower diff gearing to accommodate) I get the factory rating of 12/14.

Maybe check the Subie forums. I’ve seen a few on these tires and I’d bet it’s been discussed.

 

[ScotsSkier]

Some misconceptions here about 4WD only helping with traction. My F150 has a choice of two 4WD modes. One is with an automatic/clutched center diff (4A) that varies torque to the front wheels as necessary (similar in lots of ways - if not quite as sophisticated - to Audi and Subaru) and also a fully locked center diff (4H). The 4A setting is designed to be used in all road conditions as required (just switch it on and forget about it) and the 4H is supposedly more for off-road, deep snow etc. but does start binding the driveline in low speed maneuvering. I have played about quite a lot with both and personally in snow/winter conditions I much prefer the 4H locked setting as it does add significantly to the stability and braking performance, not just traction. In fact ford uses the basically same transmission on the Raptor F150 as well although it has additional modes that can be selected. Lower trim level 4x4 F150s (XLT and below) use a different transmission that does not have the 4A diff, just the locked 4H position.

The original Audi uRquattro turbo also came with the option to lock the center and rear diffs and locking the center diff produced similar improvements in stability and braking. Subsequently Audi moved to Torsen center diffs

 

[scott43]

I'd like to see some tests for braking distance with 4wd locked and unlocked...

 

[nay]

Always remember that the only thing 4WD is good for is getting stuck in a harder place to get out of. The SUV's you find upside-down in the snow on the side of the road were driven by people who didn't understand that.

Those people were driving the tires that it came with. Having said that, every diff locker you add makes your unstucks more fun.

I don’t get stuck until the frame is bearing full weight and all four will spin in idle. Like here.

 

[James]

So, in terms of driveline braking, one needs to have solid connections at all points, right? Does having auto lock hubs help downhill or braking? Similarly, center diffs with a fliuid coupling for variable power ditribution don't help with driveline braking?

Just wondering how many vehicles are actually available with a solid connection mode at all points?

 

[nay]

I'd like to see some tests for braking distance with 4wd locked and unlocked...

There are limited ways to test this since four wheel ABS is so integrated with electric traction control.

I have a base gear driven AWD center diff with a viscous coupler “on top” plus the locking center diff that also then locks out ABS.

4WD (locked center diff) is always mechanically superior, because as @mister moose pointed out in his excellent post, all slip is bad.

If you think about “from the wheels that slip to the wheels that grip” advertising, you don’t want wheels that slip. Electronic traction control braking systems correct this so quickly that it is entirely passive to the driver, but as @mister moose said:

Small losses of traction are information. This is the number one issue I have with modern passive electronic safety systems: they keep the driver in he dark until those limits are suddenly exceeded.

That’s a reason I really like the hybrid truck tires. I get little bits of slip and wiggle without any loss of control and I immediately know to slow down.

I’ll take feedback to the human over feedback to the computer, but at the level of mass transportation it’s really hard to argue taking control from the driver.

Also, locked axle differential > open differential. If you can lock all four and have a low range transfer case, you can idle down and crawl up I credibly steep grades in very slick conditions. This is a 14% grade descent with no brakes.


Then watch the minivan in its lowest gear just picking up speed and so pedal braking is required. The Cruiser was barely moving on that pitch to where it got dangerous and I had to go down the shoulder. I was just in AWD low range here.

Compression braking > pedal braking.

 

[SShore]

They are Rotiva AT in 275/60/R20

They make those Nokians in a truck tire? What size did you get? My sense is that once you have a vehicle that big car tires don't survive well.

 

[Josh Matta]

Both.......

but would take a 2wd +snow tires + Limited Slip over a snowtire less 4wd.

 

[nay]

So, in terms of driveline braking, one needs to have solid connections at all points, right? Does having auto lock hubs help downhill or braking? Similarly, center diffs with a fliuid coupling for variable power ditribution don't help with driveline braking?

Just wondering how many vehicles are actually available with a solid connection mode at all points?

Yes, you need a locking differential, not a limited slip like a torsen that is biasing torque, because those can always allow all the torque to one end.

Locking hubs just allow you to disconnect the entire front end so the driveshaft doesn’t spin and locking them is the same as the standard full time engaged hub.

A viscous coupler over an AWD (torsen, etc) center diff will mimic a locked diff to a point, but the oil needs spin (slip) to engage.

My Land Cruiser actually didn’t come with selectable high range 4wd, because Toyota felt the AWD + viscous coupler was sufficient. I have what is known as the “7 pin mod” to create the selectable 4wd mode.

The downside of locking diffs of course is dry pavement - the front axle has to travel a greater distance than the rear, and for axle diffs the outside tire has to travel further than the inside. This is “slip” in the form of required wheelspeed differentiation and is the only reason “all wheel drive” (or differentials for that matter) exists.

The problem with AWD mechanically is that it can allow all torque to one tire and it is really 1WD just as 4WD is really 2WD (one tire on each axle). Electronic traction control applies the brakes to a wheel that starts getting too much spin correcting this issue, unless all four wheels have low traction in which case it is just putting on the brakes. That’s why there is a traction control = off button, but now you have just open diffs again. Sucks when you have to turn off your traction system to try to get traction.

True 4WD is only achieved with 3 locking differentials, and the only vehicle you can buy new in North America in that configuration is the Jeep Wrangler Rubicon. The only other one ever sold in North America was the 80 series Land Cruiser from 1993-97.

But the aftermarket is ready and willing to assist, although most people won’t ever exceed what the computer can deliver through hydraulic torque management.

 

[nay]

Both.......

but would take a 2wd +snow tires + Limited Slip over a snowtire less 4wd.

What’s a “snow tire”?

 

[Jilly]

One thing to note. Most shops won't do the swap if your car has tire pressure monitoring and your snows don't have sensors. If they do have the sensors there may be a charge for resetting the system. I do the swap myself.

I just ignore the little tire symbol for 5 months. Electrical tape will cover it up. Just changed to the summer tires. AWD Equinox. Not sure what the snows are for brand. Driving is much quieter now though.