AWD vs FWD on snow/ice


#1

Honda CRV (awd) versus Toyota Avalon (fwd)
On an interstate drive, mostly level during snowy weather, is AWD substantially safer?
Specifically, the main threat is spinouts. Real bad with RWD but that is not in this discussion.


#2

No. AWD is handy for getting started from a dead stop when it’s slippery. Once you’re moving, AWD cannot defy the laws of physics by allowing you to stop faster than you could with FWD.

Psychologically speaking, AWD is often more dangerous, because people with AWD think they’re invincible and drive like idiots when it’s snowing.


#3

No, AWD can’t help you to stop in a shorter distance than FWD can, but when you come to a curve in the road, AWD gives one a substantial advantage over FWD. My approach is to equip my AWD vehicles with winter tires. As long as someone with AWD and winter tires drives in a sane manner, he she should be able to navigate in extreme winter weather without any problems, and that can’t be said for either FWD or 4WD.

In my experience, the vehicles that wind up spun-out and stranded in the median of a highway are those with 4WD–usually, but not exclusively Jeeps–whose drivers didn’t understand the significant limitations of 4WD–as opposed to AWD.


#4

Front weight biased cars naturally want to understeer. Understeer is when you need to turn the steering wheel more to negotiate the turn. This doesn’t matter if you have AWD or FWD. It only matters with RWD because the power goes to the rear wheels and overcome the rear wheel’s ability to grab the road. Add enough power and you spin. Rear heavy cars, like a Porsche 911, naturally tend to oversteer, or spin the rear out. Add a little power and they REALLY want to spin out.

Cars like Audi Quattro and Subaru AWD cars are essentially FWD cars with a transfer case and rear differential. The FWD versions of these cars, if they overcome traction at the front wheels just slide wide of the direction of travel, or understeer very badly. Adding AWD to those cars spreads the power to all 4 wheels so they don’t break traction so easily but they still ultimately understeer.

Is AWD safer? The handling is easier to control by a less-than-talented (heavy footed) driver. They don’t get stuck as easily in slippery stuff. Do they stop faster? NO. The same 4 tires are used to stop the vehicle FWD or AWD.

You want safer? Buy winter wheels and tires for any car used on snow and ice.


#5

I don’t like the top heavy feeling in sweeping curves with my awd equinox. I think once the front tires start to slip than the power transfer to rear does not really help as you sweep thru a curve. Would a lower CG sedan do better? Or maybe an awd sedan?


#6

Always will be better. Lower center of gravity vehicles don’t transfer as much weight from the inside tire to the outside tire in a turn. The more weight on the tire during turning, the less the ability of the tire to generate the lateral force needed to keep the car on the road.


#7

There haven’t been any FWD versions of Subarus since the early '90s.


#8

Thanks for the info but not pertinent to the explanation. They still react the same as they did in the 90’s, 80’s and now. Physics hasn’t changed.


#9

It’s Kansas, so curves are not very important. Spinning out when you hit a slick spot on the interstate is the main hazard. Stopping we understand.


#10

… and Subaru’s AWD system has been “biased” to 60% RWD/40%FWD for about 10 years. The bias will vary, depending on traction, but the “normal/default” bias is 60% to the rear/40% to the front.


#11

And the cars are still front-heavy, so the physics still applies.


#12

… that may well be true, but I have been able to drive for the past 23 years in winter conditions without any spin-outs–or even getting stuck–once I switched to AWD Subarus equipped with winter tires.


#13

I used both FWD and 4WD for 12 years in Anchorage. Biggest impact was using winter tires. FWD did fine.


#14

I would argue that if you need that advantage on a curve, you are going to fast to stop properly should you suddenly need to.

In other words, AWD is nice for getting started, but you should not consider it to be an advantage for any other phase of driving, because that leads to overconfidence.

I’d be willing to bet you were decently safe before then, too, because you don’t strike me as a lunatic driver.

The number of Subarus around here that drive like morons when the highway is covered with snow is staggering. You can tell they’re thinking they have a Subaru and therefore life is a rally race.