If the “cutting the torque by half” is confusing you, remember that the center differential is either locked or non-existent in my example*. If it wasn’t, none of the torque would go to the back axle. All the power would go to the front left and the vehicle would be stuck completely.
As an aside, I was thinking of my brother in law’s old Trooper II for the original comments. It’s normally two wheel drive, but can be shifted into four from the inside. As it doesn’t really have a center differential, it is the same as locking the center differential.
*There are 3 differentials in a full time 4WD - front, rear, and center. The center divides the power between the front and rear axles and the other two divide that power between the left and right wheels of their axles. Part time 4WD’s don’t have a center differential and power is applied directly, and evenly to both axels. The axels, of course, do have differentials which can be lockable.
I was thinking about getting a 4wd car (like a Subaru or an Audi) for my perilous wintertime commute, but I decided against it. As others have mentioned here, there are downsides (weight, cost, mechanical complexity/reliability, maintanence and running costs, etc).
The author of this essay is not hostile to 4wd, but he readily agrees that one’s choice of tires will make a bigger difference to the on-road driving experience than 4wd will.
One of the disadvantages of a 4WD that I don’t think anyone has mentioned is the fact that they are designed with large bullbars on the front which are intended to knock things down. This really isn’t helpful when all anyone does is drive these things around the city, if there should be an accident and someone steps out in front of a 4WD its going to knock them down forcefully onto the road and then in all likelihood run over them to boot. However with your average 2WD sedan in this situation the person is likely to roll up the bonnet and off to the side suffering less damages.
Also in an accident with another car a 4WD is likely to do a lot more damage… but of course when someone buys one they’re thinking of their own safety, not how safe the people they’re crashing into are.
If you’re not going to be driving off-road then you shouldn’t buy a car designed for off-road conditions.
Lemme butt in w/ a few points, having owned many of the cars discussed in this thread, and being somewhat of an AWD junkie:
Glix: you are mixing up SUV with awd vehicle. Welcome to the board, but please pay more attention to the content of a thread before posting
Philster: your classification of awd vs 4wd isn’t all that accurate. Nearly all awd systems deliver some power to all 4 wheels under all circumstances. Audis for example deliver 25% of power to each wheel under normal dry conditions.
Mastema: DO IT!!! I had a 2000 Audi A6 2.7T and that car was simply amazing. Best interior of any car on the road period, quattro is simply unbeatable, and man is it beatiful to look at. FYI, quattro is always spelled with a lower-case q
enipla: yes, many part time 4wd systems will let you manually lock the center diff.
A few general points:
modern awd systems like Audis or Subarus are bulletproof, and so the repair cost argument is a non-issue
In theory, AWD systems actually get better fuel economy because of lower rolling resitance and drag vs non driven wheels on a 2wd car, but in reality the extra weigh undoes the advantage.
As Philster mentioned a part time 4wd system is not safe to operate on dry pavement, and can dramtically affect the handling of a car when engaged.
There are many different schemes for awd available, in fact Subaru uses a different system on its automatic cars than on its manual cars. Audis quattro is acknowledged as the best, but for the most part, any full time awd system is quite capable.
4WD is great if you are off-roading or know that you’ll be dealing with severe winter weather on a regular basis. SUV’s in general and the 4WD SUV’s in particular seem to roll more easily (as in Wreck).
Gas mileage decreases as well.
However, most front wheel drive vehicles that I’ve used have been able to get almost anywhere that a 4WD can go.
Although you can generally go more places and in worse weather with a 4WD, you can also get more stuck and faster. Some folks seem to think that they are invincible with 4WD and push the boundary on reasonable and prudent driving.
My recommendation if you get a 4WD is learn how to use it. It won’t help if you don’t know how it works. We see a lot of people on icy roads go flyin’ by at 60-70 and come upon them 5 minutes later, on their top.
Oh, and to answer your question, ** asterion**, you shouldn’t drive that Trooper above 50mph in any conditions with the 4wd sytem engaged. You should also never drive it on dry pavement with the 4wd sytstem egaged. Also keep in mind that when in 4wd the Trooper will have a larger turning radius and tend to act a little “squirrely” when turning.
Setting aside all the AWD vs. 4WD for a moment. I have a GMC Yukon, 2 door, 350 V-8, 4WD (Very much a truck, not an Audi sports car) and have had it through the last 8 Chicago winters. I can probably count on one hand the number of times it has been in 4WD because of snow. I can tell you that there has NEVER been a time when I “needed” 4WD to get somewhere. I may slip into 4WD just for fun, or “because it is there” but I have not needed it. This includes the snowstorm of New Year’s day a few years back when we got something like 24" of snow in one day. I was able to drive in that mess in 2WD, with snow up to the axels. (yeah, I used 4WD, but that was an all time record snow) Granted, the truck does better in 2WD than most sedans etc, but I still think I could live happily in Chicago in all but the most severe once-a-century type storms with a 2WD car.
I understand the turning radius, but why is that with the never-on-dry-pavement or above 50 restrictions? Is it because it is 4WD or because it is selectable 4WD or something else? I have a somewhat decent knowledge about cars, but I don’t know much about drive trains or differentals.
I drive an AWD car and I got it because I had to drive regularly to Detroit and Pittsburgh year round as part of my job. It might be a little safer at prudent speeds but I don’t tend to get stuck much in any car. Just remember that no matter if it’s 4WD, AWD, FWD or RWD, you still only have four wheel brakes. Almost all the accidents I see are caused by not being able to stop, not from being unable to go.
I think ABS is worth more in the winter than AWD. I don’t drive fast in bad weather and I laugh when I get passed by someone in an AWD/4WD vehicle because they have what I believe is a false sense of security. I make a point to notice that many of the people skidding off the road in snowstorms are in AWD/4WD vehicles.
If your friend gets an AWD/4WD car, tell them to get the extended warranty. Just trust me on this.
Don’t know much about the Trooper, but I have a Pathfinder that I bet has a similar system.
I will drive on pavement in 4wd that has patchy ice and snow conditions mixed in with dry. Never had any problems. You don’t want to drive in 4wd on dry pavement when you are making a lot of turns. Definit no no. The center diff is locked and the front of the car will travel a different distance than the rear in a turn. Something has to give in this situation, and it will be wheel skip utill they day that something breaks.
In slippery conditions, this is not an issue, one wheel will spin or drag just a little bit (inches).
I routinely drive 50mph in 4wd. From a mechanical standpoint, If you are on a snowpacked road, I don’t see why it would hurt it to go faster.
On the other hand, if conditions are bad enough for 4wd, I doubt anything over 50 would be very safe anyway.
Many of the newer 4x4s alow you to put it into 4wd with or without locking the center diff. In other words the center can deliver different rotations to the front and rear, instead of ‘locked’ constant speed to both. My wifes Grand Jeep is this way. If the center diff is not locked, you can drive on dry pavement all you want.
AWD is a very nice system, a good, no great compromise between 2wd and 4wd. The drawbacks are few and the benefits are huge (most have been mentioned here)
One more benefit - in general - much higher resale value.
Bernse may be right in saying that this is a overgeneralization, but it certainly has some truth to it. With 2WD, you are forced to pay close attention to the “traction coefficient” of the road you’re on – you won’t even get going if you don’t. With 4WD, you can rapidly get up to cruising speed without paying attention to what the road surface is like today. Come that sharp curve, you may find out in a hurry.
Damnit, I was right the first time. I just second guessed myself. Lockable axle differentials are aftermarket and usually only found in “hill climbers”.