AWD vs FWD & Limited Slip Differential


#1

What is the difference between AWD & Full Time 4WD? Can a vehicle have AWD (or 4WD) and not have Limited Slip Differential? If Limited Slip Differential gives traction to the wheel or wheels not spinning uselessly (like when stuck in mud or slipping on ice) & an AWD or 4WD vehicle does not have LImited Slip Differential, what advantage does that AWD or 4WD give you over FWD?



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#2

“Limited Slip” is seldom if EVER used on an axle that must steer the vehicle. It can result in loss of steering control.

AWD puts some type of “limited slip” differential gearing between the front and rear axles, allowing full-time engagement. 4WD locks the front and rear axles together with direct gearing with makes driving on clear pavement difficult and dangerous because cornering can not be accommodated without tire slippage…


#3

Your questions are too involved to give a simple answer in a post but…
Mechanical limited slips do appear in some FWD cars and RWD on the same axle with good though varying affect affect. The problem is, they never transfer as much power as a full lock and only on one axle. Traction control is a good and safer compromise as it’s much cheaper to add to a fwd, works nearly as well as limited slip but at the expense of brakes while providing better modulated control for steering on the front.

AWD though technically still only driving two wheels, but on different axles, is a huge advantage. For good around traction on slippery roads, but not off road, the awd with traction control set up seems to help overall performance in slippery driving the best.

Technically, 4wd is confused with awd unless you stipulate part time 4wd which locks the center diff to 50/50 distribution; great for off road and slow going, but a potential accident causing set up at higher speeds on slipper roads.

My SUV and others try to give you “all” these traction options and are more expensive and require a little more thought when driving than dedicated awd or part time 4wd systems.

Don’t equate mud to ice. Two different applications. AWD w traction control for ice/snow; part time 4wd with differential locks or limited slips on each axle for mud, are the two best for each. THEN you may add automatic crawl control modes…etc, it’s a whole seminar beyond a post.

This entire discussion is predicated around having the appropriate tires…all of this stuff is for not if the tires don’t grip effectively on the particular surface you are talking about.

Some flatlanders might say 4wd/awd will get you out of a ditch, but will not keep you from getting into one. Foolishness gets you into a ditch regardless of what you drive and a good 4wd/awd driven sanely is ALWAYS better than than 2wd in all poor traction applications from keeping you out to getting you out, of ditches. You have to decide the most cost effective way for your needs and the sacrifices you are willing to give up for your drive train choices.

Get more complete answers yourself…start “googling” !


#4

I appreciate your response. I have tried looking this up online but often the info is too complicated for me as they often refer to stuff I am unfamiliar with. There was no auto mechanics class in my school & I had never had anyone in my life that worked on cars. I ran out of ideas as I know no mechanics in my personal life & thought someone helpful like you could help me. This is very helpful!

Years ago I took an auto mechanics for the ignorant class and the mechanic told us that only a dummy buys a vehicle without LSD, but when I went to look for one they seem fairly rare. This was before traction control & stability control, so maybe this is not relevant now. I did not know.

I have 4 large dogs & a spouse. I want something that can actually accommodate my family. When I get my next vehicle I want one that I won’t want to replace until the end of time. I am more likely to be stuck on ice than in mud. We have periodic icy snows, not mudslides. Now I have a Prius & there is no fitting 4 large dogs in there. I replaced the tires it came with in part because there was just no traction. Gas mileage is great and all that, but I like to keep the car on the road.


#5

There a getting to be many types of AWD and 4WD systems on cars sold today. The differences can be very technical with advantages and disadvantages to all. In general AWD systems are controlled by the car’s computer and sensors and the driver just drives. There are no buttons to push. These systems are great for passanger cars but are not strong enough for many “truck” applications like carrying heavy loads or towing big trailers.

Therefore most truck and truck based SUV’s have 4WD systems that have a button, or level, that engages the 4WD systems. Most of the time you are driving in 2WD mode which is the rear wheels doing the driving. Push the button and you go into 4WD when you need it. Using these systems all time in 4WD will cause damage and very poor gas mileage.

When you are actually on snowy and icey roads either 4WD or full time AWD will feel about the same to the driver. You’ll be able to start on snowy roads with a minimum amount of slipping. If you put winter tires on your vehicle you’ll take off in snow with almost no slipping at all. Neither AWD or 4WD does much to help you steer or brake. These functions rely on traction from the tires and the ABS braking system in the car. Therefore, I prefer winter tires even on 4WD and AWD vehicles. I like to control where I’m going and stop in the shortest distance possible.

Now for limited slip differentials. They aren’t used that much in AWD or 4WD systems. Most limited slip differentials are in 2WD pickups and perhaps some higher performance cars. If you have a limited slip differential you won’t spin the wheels as much, but when you do spin the wheels you can have the back of the car whip around on you in a hurry. 2 spinning wheels gives virtually zero lateral stability. I have an '04 T’bird with a limited slip rear end, and it is a RWD car. On dry pavement with the traction control off the car just digs in an takes off in a very rapid fashion with no wheel spin. In snow with traction control off I can’t drive the car. The back tires just spin and it slides sideways and is uncontollable. With traction control on I can hardly drive the car because the traction control kills the motors power as soon as it slips. With winter tires I can drive the car in snow, it is an adventure so I minimize winter driving.

You want something big enough for your dogs and good traction. If you want a new car check out the Toyota Venza. It is now available in AWD with the 4 cylinder motor and gets about 28 mpg on the highway. Not bad for a fairly big car. If you live in snow country a Venza with winter tires, AWD, and traction control (all standard in that model) would be virtually unstoppable, you could go anywhere as long as you could see the road.


#6

I had not thought of that. I had been reading about the 2010 Chevy Equinox, 2010 GMC Terrain, and the Ford Escape. I need to see if I can actually get 4 large dogs & a husband in any of them. Someone suggested just give up and buy a mini van, but I haven’t gone there yet. There is also the Subaru Forrester. I have always liked its big windows. The Prius has many blind spots & I am not wild about that.


#7

Four large dogs and a husband is now called a “Family”?? Does the husband ride in the back or the front?


#8

It sounds like you’re more into traction requirements of AWD. But if your not in hilly terrain, even 2wd with traction control can serve you. By the way you talk, if you’re considering a 4wd type vehicle, I would recommend first a car based SUV/van with awd…not a truck based.
4 dogs sounds like a Honda element which has excellent reliability. It is comfy up front and a hose out affair in the back…they are used by the canine crew for the state police in our state.
Otherwise, I’d look at things like compact suv’s with easily removable seats. (Escape/RAV/CRV/Forester etc) they are all functional, economical and will serve your dog needs.
Best reliability comes with the RAV/CRV/Element/Forester
Traction control newer versions have defeat switches when the snow gets deep, which allows you to throttle up. So traction control devices are not an issue any more for deep snow/mud.

My first recommendation for reliability, 4dogs, 2 people and AWD is the Element…that’s what it’s made for.

If you are considering a truck…Limited slips are used in lots of trucks, 2 or 4wd where traction control devices and towing/off road don’t like to go together. ALL Tacomas come with limited slip 2 or 4 wd and one with a cap on back for the dogs may be another alternative with a cab of your choice for people. Likewise for Ford 150, GMC Sierra. I would not recommend Chevy or Ford compact trucks; THEY are dogs.


#9

Thanks! I was thinking SUV or Crossover, not truck. I just assumed that SUVs and Crossovers were car based, not truck based. Now I guess better be sure. My husband has a truck & that is an bumpy ride. I guess I want it all, but I want to end up with the important stuff!


#10

SUVs are very nebulous…It’s really so tough to tell. Some truck based SUVs nearly handle and ride as well as car based.