All Wheel Drive Does Not Make You Safer

Every year right around this time, millions of consumers are tricked into a massive financial and lifestyle mistake as the natural incompatibility of snowy roads and safe driving take them by surprise.

“I know Mr. Money Mustache insists that I drive only efficient cars, but that’s because he lives in the dreamy semi-desert of Colorado where it never snows. Where I live, the roads are ice-packed for the entire winter, and you’re doomed if you don’t have All Wheel Drive. Therefore, I will buy a enormous four-wheel drive truck for the safety of my family. Or at least a Subaru.”

This is just plain wrong, and as a recovering gearhead, I need to make a public statement on it.

Just like any other great marketing-fueled deception, automakers have captured both our irrational fear of loss and desire for status, and channeled them into a product line that just happens to be more profitable for them. And it’s shocking how well it has worked, as even some of my most esteemed readers have been writing in to ask for advice on “which AWD vehicles are Mustachian?”

The answer is “Whichever one the Forestry service or the Military issues to you when you show up for duty in an area without roads*.”

Because for the rest of us, it’s Hip and Knee Drive for your shoes, Chain Powered Rear Drive for the bike, and Front Wheel Drive for those rare occasions you need to use a car.

The reason I can state so confidently that the AWD hype is pure marketing bullshit is simple physics. Although this was one of my favorite subjects in engineering school, you don’t need a degree to understand it fully and cure your desire for AWD.

Car safety depends at the core on two things: not crashing into anything, and not letting anything crash into you. To accomplish those goals, the ability to steer your car in the direction of your choice is the top factor, with braking coming as a close second. A certain amount of acceleration is important as well, but not nearly as critical as the first two: note the extremely low collision rate of transport trucks and city buses per mile traveled.

Every car, truck, and SUV has four wheels. And every one of them has front-wheel-steering and all-wheel braking. So we’re all on a level playing field so far. The place where the safety in accident-avoidance starts to diverge is:

• How firmly the car sticks to the road (more grip means more safety)
• How effectively the car lets you change direction or speed (cars with a lower center of gravity and stiffer suspension are safer)
• How the power and braking affect vehicle dynamics (applying power to the rear wheels while cornering tends to break the grip and cause you to fishtail and spin out – this is why rear-drive-only vehicles like sports cars and pickups are more dangerous in snow, but front-drive works well)
• Fancy computerized add-ons that compensate for human limits (ABS and Vehicle Traction/Stability Control) can increase safety by modulating power and brakes.

That’s it for the physics. You’ll note that there is not much in there that would allow cranking all four wheels, instead of just the front wheels, to make you any safer. And in some cases it will send you into the ditch faster than front-wheel drive.

Note the implication of this: If anyone gets an AWD vehicle “for safety” but uses it with all-season tires, they have performed a Consumer Sucka Fail. A front wheel drive vehicle with snow tires would have more grip.

According to this Consumer Reports test on snow tires vs. AWD, the tires were by far the most important factor. And only 12% of AWD vehicle owners bothered to put snow tires on their vehicle, meaning 88% of all-wheel-drive vehicle purchases were wasted, because the drivers could have achieved better performance at lower cost in a front-wheeler with snow tires.

So When IS AWD useful?

All wheel drive is a performance feature, not a safety feature. With all other things being equal, AWD lets you accelerate more quickly on slippery roads. This is usually a bad thing, because it masks the true slipperiness of the road from you, leading to overconfidence which will put you into the ditch, courtroom, or emergency room. But it is useful if you need to plow through unusually deep snow in conditions that would normally get you stuck (for example a steep snowy driveway, or if you run a snow plow). It’s also useful on extremely steep unpaved roads or in areas with no roads at all – places you are unlikely to need a car.

But Why Does Mr. Money Mustache Hate AWD so Much?

I have nothing against all wheel drive. It’s a cool bit of mechanical engineering that gives a vehicle superpowers. Whenever my son and I make a LEGO Mindstorms or VEX IQ robot, you can bet we’re going to give that sumbitch AWD or even a set of tank treads, because hey, why not?

The thing that pisses me off is that people have started using AWD for no reason on paved roads. Here we are, a society who has spent trillions of dollars building a road network so wide and glassy smooth that you can get almost anywhere in the country in all seasons even if you are driving a 73-foot tractor trailer rig, and we are still wasting money driving off-road vehicles on it.

Make no mistake: In a gas-powered vehicle, AWD requires huge sacrifice in weight and complexity. Hundreds of pounds of steel shafts, gears, lubricating oils and reinforcements are required to get the power from the engine to that extra set of drive wheels. And not only must you pay to carry that dead weight around for the life of the car, you burn even more gas fighting the extra friction of the additional gears every second the car is moving. And then you have to pay to maintain and repair all those extra moving parts. It’s like carrying all your camping gear on your back every time you leave your house. It is also akin to a man attaching a set of 13-pound Decorative Testicles below his real ones, just for show. You would do it if absolutely required for a social event, but not when you actually had to get some work done.

My Subaru Story

Back in the day, even Mr. Money Mustache slipped into the Subaru trap at one point. It was a 2004 Impreza wagon. I bought it for the impressive cargo space, but sold it just a few years later for the abysmal gas mileage. Even with a 4-cylinder engine and a manual transmission and my best attempts at hypermiling, that little machine could suck down gas at 27 MPG on the highway, meaning it consumed as much fuel as my 15-year-old city bus of a construction van does. By comparison, the 2005 Scion xA I replaced it with holds the same number of people, but has averaged about 42 MPG in its life with me. But at least those Subaru years gave me plenty of time to evaluate the effectiveness of all-wheel drive**.

What I found was just what physics would suggest: it’s all in the tires. The car came with reasonable all-season tires, which gave it fast acceleration and average stopping power in blizzards. On the other hand, I would end up Dukes of Hazzarding through slippery intersections because the rear wheels would break their traction more easily than a front-drive car. On the positive side, the car could do outrageous drifting power doughnuts in an empty ski resort parking lot – a longstanding Subaru owner tradition.

Later I upgraded to a set of Pirelli 215/45ZR17 performance tires on fancy wheels (hey, I was just a clueless lad back then), which greatly improved its handling on my area’s usually-dry roads, but turned it into an all-wheel-drive toboggan in the snow.

I vividly remember a moment in my town’s level, well-plowed Lowe’s parking lot, pulling out with a small load of lumber. It was a sunny but crisp day in January, so the snow was melting only slowly. I found myself stuck right in the pedestrian crossing in front of the store, with all four of those big alloy  wheels whirring cheerfully but uselessly as they polished the packed snow and I went nowhere. It took a couple of friendly but sarcastic contractors to push me out by hand. They mocked my vehicle for not being a truck, but the real joke was the tires.

 But why is my Aunt’s Subaru so much better in snow (even braking) than my Prius?

Last year my van pulled a heavy load up a grassy hill covered with 8″ of snow. Front wheel drive is more than enough.

The tires are the biggest thing, but a few other factors than can also affect traction:

A wheel and tire combo with a longer contact patch can grip the snowy road better. Larger diameter, narrower width, taller sidewall profile, softer rubber compound, and lower air pressure all contribute to this. The Subaru comes with larger, softer tires than the Prius.

A heavier vehicle can crush the snow enough to get slightly more grip in certain conditions, but this is tricky since extra weight also means more trouble changing directions. Extra weight also makes you more lethal to everyone else on the road, which would make it a pretty selfish way to try to defend yourself. If you choose to play this game, just be honest and add machine guns instead.

Higher ground clearance allows you to skim over deeper snow without scraping the car’s belly. But this is a smaller deal than you’d think. For example, the Nissan Pathfinder SUV has 6.5 inches of ground clearance, while the Toyota Prius is only an inch lower at 5.5. A road with even 5 inches of snow is insane to drive in any vehicle above about 25 MPH, so you might as well get out your mountain bike or cross country skis.

The Ultimate Solution

The first choice, of course, is to design your life so you don’t need to drive in the snow very often, or very far. I accomplished this partly by moving away from the extremely snowy area of Canada where I grew up. But you get equal effect by doing your house and job shopping with car commute avoidance in mind. A person with your level of skill is definitely entitled to work from home on snow days – your boss will agree.

Oddly enough, once I laid the ground rule of no snow commuting, the freedom from cleaning off cars and driving them in snow has been one the longest lasting bits of happiness I have ever experienced: 15 years of smiles and still going strong. Nowadays, although I argue strongly for snow tires, I don’t own any – because I just don’t bother driving on those rare days it snows in my own area.

Second best: Snow Tires on Dedicated Rims

Blizzak WS-80 – slightly pricey, but your Honda Fit will outperform Jeep Grand Cherokees once you outfit it with these. Highly recommended for extremely snowy areas.

This part is really easy.  We now know that SUVs and AWD are not useful for those driving on paved roads. We know that summer tires and even all season tires are death traps compared to snow tires. I’m serious about this: there is a night and day difference in snow grip between all season tires (sometimes referred to by driving professionals as “no-season tires”) and good snow tires, because of the different rubber compounds and tread patterns.

But you don’t want to take your car to a mechanic twice every year and pay to have summer and winter tires swapped. This costs time and money, and damages the tires and rims. Instead, you simply get a second set of rims with snow tires permanently installed.

In the US, you just go to TireRack.com, look at their winter catalog, and pick out a set of wheels and tires that are guaranteed to fit your car. They come via UPS, and you jack up your car and swap them on one at a time, just as easy as putting on the spare. Any dedicated tire shop or Costco is also a good choice (Tire Rack will still help you get an idea what a good price on tires and wheels looks like). And as usual, the auto dealer is to be avoided – they’ll just try to sell you two thousand dollar tires and rim sets, or worse,a brand new model with AWD.

Happy Holidays, and may this set of snow tires be the last you ever need.

* If you read all this and insist on disobeying Mr. Money Mustache to your own detriment, the least ridiculous new AWD cars on the market right now are the Subaru Impreza wagon (they have improved it to 33MPG highway) and in the Large SUV category, the Subaru Forester (up to 32 hwy). Another good choice for large off-road camping families with an extreme money surplus is a 2010-ish Honda CR-V. SUVs larger than this have no rational reason to exist at all – just get a van.

** Thanks to my upbringing in Canada and various subsequent snowboarding trips around North America, I’ve also snow tested a few other all-wheelers: the Subaru Legacy/Outback, WRX wagon and Forester, Jeep Wrangler and Grand Cherokee, Toyota Tacoma and 4Runner, Audi S4 wagon, Nissan Pathfinder, Ford F-250 pickup, Chevrolet Trailblazer and Traverse, Honda CR-V and Element, and even an Eagle Talon turbo AWD. Diagnosis: It’s all in the tires.

Further reading on cars: Top 10 Cars for Smart People

Car and Driver: Snow Tires Still Beat Four Wheel Drive

Jalopnik: let’s settle the Winter Tires vs AWD debate forever, and Snow Tires: to buy or not to buy