Normal bad driving conditions are heavy rain, snow, and ice, commonly found on the roads during periods of bad weather. Not offroading, climbing rocks, etc.
What exactly makes AWD/4WD that much better than FWD/RWD?
Why is 4WD better than AWD? Don’t you have to “turn it on” and if so, isn’t that worse if you hit a patch of ice/standing water/whatever, than AWD?
I vaguely understand that all axles vs only the front/rear axles are engaged, but I don’t understand the difference between AWD and 4WD, and not really why some roads are “chains required unless AWD/4WD” – is it that much safer that you wouldn’t need chains on the tires?
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AWD is really more of a marketing term for cars that have “always on” 4WD, like some Subarus. The term 4WD is typically for when you can turn it on or off. It’s good for slippery conditions because it gives you more ability to push the vehicle in the desired direction.
All wheel drive cars typically have a series of differentials, one to split front/back, and another to split left/right on both ends. This allows for a variable amount of power to reach each wheel, and each wheel can rotate somewhat independently of the others.
A 4wd car uses a transfer case to evenly divide the power between the two sets of wheels. This ultimately means that with a 4wd car, you always get the same number of tire rotations on all the wheels over the same time. While this sounds right, if you’re cornering, your inside wheels need to spin less. A 4wd car will experience slippage and loss of traction since they will have wheels that rotate the same amount but try and cover different distances.
This is why AWD can be always-on, but 4wd is usually a selectable mode — it has a specific use case, and it can make things worse outside of that use case.
For reference, I’m someone that: (1) will get up in the middle of the night if it snows just to go driving for fun. And (2) has owned and driven all the different drive types in the snow. Here are my thoughts:
There are three main things that allow a vehicle to **go** in snowy and icy conditions. These are in no particular order.
1) The use of true winter tires designed for snow and ice. All season tires are no match for winter tires.
2) The percentage of the vehicles weight on the drive wheels. AWD and 4WD vehicles have 100% of their weight on the drive wheels (can’t do better than this at slow speeds). FWD cars often have 60 to 70% of their weight on their front drive wheels. RWD vehicles often have 30 to 50% of there weight on their rear drive wheels.
3) Driver experience driving on snow and ice. This, obviously, isn’t related to the car, but it is roughly as important as 1 & 2 above so I wanted to include it.
Note that above I said “to **go**”. When it comes to stopping and turning AWD and 4WD don’t help a lot. They can help some wen turning, but do almost nothing to improve stopping. This, in my view, actually makes AWD and 4WD less safe for inexperienced drivers. In slippery conditions, it is too easy for inexperienced drivers to get moving, and get moving fast, without realizing how slippery it is. Then when they need to stop or turn, they can be in trouble. A FWD or RWD car makes if harder to get going, and is thus safer.
This makes good winter tires the safest and usually cheapest option to drive safely and get where you need to get in slippery conditions.
Now don’t get me wrong. Four of my six current vehicles have 4WD or AWD, and I wouldn’t have it any other way. Combined with good tires, and an experienced driver these will go through amazingly bad conditions — and do it safely. They just present the real risk of getting inexperienced drivers going too fast in bad conditions.
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