Why your SUV sucks in the mountains

[Peruvian]

I would refute that. Growing up in New England, it's extremely common for people to have driven with dedicated winter tires. I think it's totally insane.


Among the 84 percent of snowbelt drivers who will prepare their car for winter weather, only a quarter (25 percent) plan to equip or already have equipped their vehicle with winter tires this season.

https://www.prnewswire.com/news-rele...300001625.html

Considering most Americans don't have $500 in savings coming up with $500 or so to purchase snow tires is a stretch for many. No one expects they will be the ones who can't stop, get stuck, or get in a car wreck so the decision matrix makes it easy to skip this expense. Of course with a $500 auto insurance deductible, one crash can wipe out your assumed savings.

[zartagen]

4wheel drive doesn't equal 4 wheel stop.

That's a stupid fucking quote. Every car, 2wd or 4wd has brakes on all four wheels and has "4 wheel stop."

[auvgeek]

Considering most Americans don't have $500 in savings coming up with $500 or so to purchase snow tires is a stretch for many. No one expects they will be the ones who can't stop, get stuck, or get in a car wreck so the decision matrix makes it easy to skip this expense. Of course with a $500 auto insurance deductible, one crash can wipe out your assumed savings.

Your point is a good one. Skip the fancy 4WD SUV (or pickup) and put snow tires on an old FWD Corolla. A problem is the average American can finance a nicer car but can't necessarily finance snow tires except via cc with a super high interest rate. Personally, I think the US in general would be much better if people were less willing take on debt and more willing to save for a rainy day. But that's a bigger conversation.

"Life is hard; it's harder if you're stupid."

[anotherVTskibum]

Okay, guess that attitude is more prevalent than I ever imagined. I thought anyone who drives a fair amount in the snow would know tires beat 4WD any day of the week, and also that 4WD doesn't help at all with deceleration, which is the cause of most accidents.

Honestly thought this thread was gonna be about the high COG of SUVs, which is a well-known issue. Subarus have their downsides, but it's nice to have a low COG and as much clearance as your average SUV.

While I agree that an AWD wagon with four snows on it is a lot better than an SUV or (even worse) a pickup on a mostly plowed road, 4WD does affect stopping, at least in the one A vs B test I've seen:

https://www.youtube.com/watch?v=8bXdXRbc2Rc

and from last winter
https://www.youtube.com/watch?v=EMnT1gCYjP8

[Dromond]

I think that the physical hassle of needing to swap and store the tires can’t be discounted. Many people don’t have the space and just don’t want to take on another chore. It doesn’t help that the highway patrol here often lists passes as chains/4wd required and pay no attention to winter tires. That corolla with blizzaks is going to be fine while the 4wd pickup with bald tires is not.

[auvgeek]

While I agree that an AWD wagon with four snows on it is a lot better than an SUV or (even worse) a pickup on a mostly plowed road, 4WD does affect stopping, at least in the one A vs B test I've seen:

https://www.youtube.com/watch?v=8bXdXRbc2Rc

Interesting. But, as he said in the video, it has to do with the brake bias of the front vs rear wheels -- the brake bias is changed by the (locking) transfer case in a vehicle that has selectable 2WD vs 4-hi vs 4-lo. Which I didn't know, so thanks for sharing. But still, most modern SUVs no longer have locking transfer cases -- either they're regular AWD or they have that stupid selector knob for the "mode" (rut, sand, snow, gravel, etc).

But still, if we want to play semantics, it's not the fact that you have power to all four wheels, it's brake bias. And frankly, I don't know the general front vs rear brake bias of a FWD car vs 4WD/AWD SUV. Maybe someone else does?

[GPP33]

While I agree that an AWD wagon with four snows on it is a lot better than an SUV or (even worse) a pickup on a mostly plowed road, 4WD does affect stopping, at least in the one A vs B test I've seen:

https://www.youtube.com/watch?v=8bXdXRbc2Rc

and from last winter
https://www.youtube.com/watch?v=EMnT1gCYjP8

This works with 4wd vehicles with locking transfer cases, most of your SUVs running around are AWD without a locking transfer case though. I can make all kinds of arguments about how a 4WD manual with a good driver can out perform an equivalent 2wd in stopping and emergency evasive maneuvers but most 4WDs are handicap by incompetent drivers so it's a pointless argument. Most people are driving automatics and just slam on the brakes and let the ABS computer decide how to handle the situation in which case there probably isn't a difference between an equivalent AWD and 2WD when it comes to avoiding something in front of you. Starting, turning, maintaining your trajectory (i.e. not randomly spinning out), AWD/4WD will win every time.

[auvgeek]

This works with 4wd vehicles with locking transfer cases, most of your SUVs running around are AWD without a locking transfer case though. I can make all kinds of arguments about how a 4WD manual with a good driver can out perform an equivalent 2wd in stopping and emergency evasive maneuvers but most 4WDs are handicap by incompetent drivers so it's a pointless argument. Most people are driving automatics and just slam on the brakes and let the ABS computer decide how to handle the situation in which case there probably isn't a difference between an equivalent AWD and 2WD when it comes to avoiding something in front of you. Starting, turning, maintaining your trajectory (i.e. not randomly spinning out), AWD/4WD will win every time.

Solid post all around. What I was trying to say, but likely stated better.

[simple]

I use my hill decent control button in my Audi q5. That plus manual shift mode makes stopping on ice super easy. With dedicated snows this SUV is a beast on snow and ice.

[I've seen black diamonds!]

AWD with all season tires will often get you up a slick hill better than FWD with snows. I suspect some folks experience this and think, "I didn't get stuck! I don't need snow tires." Somehow fear of getting stuck is more prominent than fear of not stopping.

[anotherVTskibum]

This works with 4wd vehicles with locking transfer cases, most of your SUVs running around are AWD without a locking transfer case though.

...and I'd be really interested to see a similar test repeated with one of those, or perhaps more than one—I'd be very curious to see if the various AWD mechanisms introduced some level of linkage between front and rear that increased the effective braking force applied by the rear wheels.

Starting, turning, maintaining your trajectory (i.e. not randomly spinning out), AWD/4WD will win every time.

...there's a reason they have different classes for 2WD vs A/4WD in rally.

With that said,

most vehicles are handicap by incompetent drivers so it's a pointless argument

.

FTFY.

[jamal]

Interesting. But, as he said in the video, it has to do with the brake bias of the front vs rear wheels -- the brake bias is changed by the (locking) transfer case in a vehicle that has selectable 2WD vs 4-hi vs 4-lo. Which I didn't know, so thanks for sharing. But still, most modern SUVs no longer have locking transfer cases -- either they're regular AWD or they have that stupid selector knob for the "mode" (rut, sand, snow, gravel, etc).

But still, if we want to play semantics, it's not the fact that you have power to all four wheels, it's brake bias. And frankly, I don't know the general front vs rear brake bias of a FWD car vs 4WD/AWD SUV. Maybe someone else does?

Brake bias used to be done with a proportioning valve. The way they work is that equal pressure is sent to front and rear up to a certain point determined by the valve. After that, rear pressure is lower because under hard braking you transfer weight forward and the fronts do more work. More modern cars just let the abs figure out out. Either way, with low traction and braking forces the brakes will be well below the range where the biasing occurs. However, the actual brake torques at the wheels are not 50:50 because the rotors and caliper piston area are bigger up front. Generally, it's about a 70:30 ratio. For the best performance, you want the brake forces to match the weight distribution. With low traction, low braking forces and very little weight transfer, that's going to wind up being pretty forward biased. The reason for that is because you don't ever want the rear brakes to lockup first, and optimum brake distribution is most important when braking hard.

On a truck with rear drums and maybe no or not great abs, being in 4wd is definitely going to make a difference as shown in the videos. I don't imagine there is much difference in how abs and brake biasing works between more recent cars and trucks, but an SUV probably has closer to 50:50 weight distribution than a fwd car, so the brakes just never provide enough force at lower speeds.

I'd like to see a followup using a subaru or something with and without the awd engaged (automatics generally have a fuse holder to disable the transfer clutches), I'm not sure you would get much of a difference. Plus those clutches tend to be more open under braking.

[californiagrown]

The snow level where i go skiing means i drive 40 miles on wet pavement, and the last 10 miles (at most) on snow. no reason to get dedicated snowtires. Never have an issue starting up a hill as long as im gentle, and never have an issue stopping unless i have the wheels cranked to one side or come in too hot. Pretty easy to just pay attention and brake in plenty of time so you dont have to rely on excellent grip (especially because my snow driving is a very limited part of the ski trip). If the roads are ice (refrozen hardpack or refrozen rain) then you pretty much need studs, otherwise you just gotta really pay attention to your momentum and be smooth.

Attentive driving goes a REALLY long ways though. That said, i rode my last tires down so low that on the final pow day of last year that i got a flat that my mechanic refused to try and fix haha. Have a new pair of Cooper ATWs on there now so that should be a nice improvement.

[XXX-er]

I use my hill decent control button in my Audi q5. That plus manual shift mode makes stopping on ice super easy. With dedicated snows this SUV is a beast on snow and ice.

exactly so you have bought the best traction you can possibly have

instead trying to rationalize why you don't need to spend money on 4 real snow tires

this whole rationalization thing is very simliar to people who say " I do fine on telemarks skis "

when they would do finer if they bought a whole binding

[simple]

That pulling a fuse trick on Subarus is long gone. Like 15 years or more gone....

[auvgeek]

Brake bias used to be done with a proportioning valve. The way they work is that equal pressure is sent to front and rear up to a certain point determined by the valve. After that, rear pressure is lower because under hard braking you transfer weight forward and the fronts do more work. More modern cars just let the abs figure out out. Either way, with low traction and braking forces the brakes will be well below the range where the biasing occurs. However, the actual brake torques at the wheels are not 50:50 because the rotors and caliper piston area are bigger up front. Generally, it's about a 70:30 ratio. For the best performance, you want the brake forces to match the weight distribution. With low traction, low braking forces and very little weight transfer, that's going to wind up being pretty forward biased. The reason for that is because you don't ever want the rear brakes to lockup first.

On a truck with rear drums and maybe no or not great abs, being in 4wd is definitely going to make a difference as shown in the videos. I don't imagine there is much difference in how abs and brake biasing works between more recent cars and trucks, but an SUV probably has closer to 50:50 weight distribution than a fwd car, so the brakes just never provide enough force at lower speeds.

I'd like to see a followup using a subaru or something with and without the awd engaged (automatics generally have a fuse holder to disable the transfer clutches), I'm not sure you would get much of a difference. Plus those clutches tend to be more open under braking.

Thanks for chiming in. As usual, I learn tons from your posts on cars, esp Subies.

[plugboots]

Thanksgiving anecdote.
My B-I-L is spouting off that the Cherokee was better than the X5 in the snow last winter. I asked what tires he had on the X5. "I don't know." Well then I asked if he bought it with the M-Sport package or the one of the summer tire packages or options. "I don't know."
Well, I said that the Cherokee doesn't even come with a summer tire option, so big wide summer tires are of course going to perform worse in snow than the skinnier all-seasons on the Cherokee.
"Well all I know is that Mrs. B-I-L couldn't get down the alley with the X5."

[jamal]

This is a classic

https://www.youtube.com/watch?v=CuTXUcoGdhw

[carlh]

AWD Stick shift BMW wagon with performance winters works great in rain and snow. RWD bias to do donuts the front wheel traction to straighten out.

[Mallthus]

Snow tires on Corolla - CHP/CSP/etc: “Sorry, chain law is in effect. You’ll need to put on chains or you’re not going through.”

Summer tires on dumb CUV with AWD - “Go ahead. Be safe up there.”

The reasons to have AWD/4WD aren’t always based in fact, but they are rooted in reality.


Sent from my iPad using Tapatalk

[PNWbrit]

yeah but he is british and they can't drive

That's funny from an Asian guy.

[plugboots]

Snow tires on Corolla - CHP/CSP/etc: “Sorry, chain law is in effect. You’ll need to put on chains or you’re not going through.”

Summer tires on dumb CUV with AWD - “Go ahead. Be safe up there.”

The reasons to have AWD/4WD aren’t always based in fact, but they are rooted in reality.

I get your point, but they will check for the M&S logo on the tires, and summer tires don't have that.

[Toadman]

AWD with all season tires will often get you up a slick hill better than FWD with snows. I suspect some folks experience this and think, "I didn't get stuck! I don't need snow tires." Somehow fear of getting stuck is more prominent than fear of not stopping.

Um, no, your first sentence is not correct. Simply put, the device that provides traction to a vehicle are the tires that contact the surface. All season tires don't have the same traction as a winter tire. It doesn't matter the drive train, it matters what rubber meets the road. But the second sentence is probably what gets people driving an AWD vehicle into trouble with all season tires. Probably gets them into trouble with snow tires too, because I'm still amazed when travelling in the mountains how fast people drive on compact snow and ice. They must think those studded tires are going to stop them just as fast if they were on dry pavement.

[Toadman]

What about tires with macho tread but all-season rubber? Doing the snows + steel wheels vs. new M+S now. M+S were fine on my AWD wagon last year but it's time to replace them.

Specifically thinking about Yokohama Geolandars right now, if anyone has opinions on those.
https://www.tirerack.com/tires/tires...cleSearch=true

You'd be okay the first season on a set of these. Just know that they aren't going to perform as well in cold conditions, below 32F like a true winter tire will. If you've got worn winter tires and looking to replace with the Yoko's, you will still eventually should look to get a set of winter tires after about 12k miles on the Yoko's.

[I've seen black diamonds!]

It doesn't matter the drive train, it matters what rubber meets the road.

Simply put, you might be oversimplifying things.