Why Few/No AWD Pickups?

Factual Questions
1

I was doing some browsing since I’m thinking of either replacing or supplementing my 2WD F150 with something a bit more suitable for playing in the snow. There are plenty of full-time AWD cars (such as the various Subarus) and plenty of 4WD pickups.

Given that most pickups are never taken offroad and the worst conditions they encounter are ice, snow and rain (just like most passenger cars), is there a good reason why truck manufacturers aren’t producing models with full-time AWD?

Is AWD that much more expensive/complicated/fragile than the “traditional” 4WD found in most trucks (not suitable for dry pavement, requires shifting into 4WD mode, generally featuring 4WD hi and lo)? Perhaps it’s unsuitable for towing trailers or some other purpose to which pickups are normally put?

2

That’s probably the reason. People don’t need AWD. If they do, they buy 4WD.

3

The Toyota Land Cruiser and some Land Rover/Range Rover vehicles are all wheel drive, as is the H1 Hummer, all of which are legitimate off-road vehicles. The reason “pickup trucks” from Ford, GM, and Chrysler still use locking hubs rather than full-time all wheel drive is two-fold: one is that it is a mechanically more complex system, requiring additional limited slip or viscous coupling differentials (between front and rear, and between the normally inactive wheels), whereas most 4WD pickups have just a locking differential on the inactive wheels and locking hubs that freewheel in 2WD mode. The second is that adding AWD to a truck would probably require extensive redesign of the suspension and steering mechanism as well as the tranny, and despite the premium price commanded today by many trucks these vehicles are esssentially the same under the shell (except for electronic engine management) as trucks of three and four decades past, still riding on leaf springs and a live axle in the rear, and an ungainly steering system which allows a massive Ackermann error (the different between the steering centers between the inside and outside wheel).

So in answer to your question, the reason is strictly cost; the Big Three want to squeeze as much profit and put as little development into pickup trucks as possible. Toyota has been building a robust AWD system and coil spring suspesion in a truck-weight vehicle for a couple of decades now (starting in full with the Series 80, but in some models of the Series 70), and it has a reputation for taking the kind of abuse that would break an F250 in half.

Stranger

4

In the 70’s a few trucks were offered with full time 4WD. It sucked. The differential between front and rear wheels was an open diff, not even limited slip.

With open diffs front and rear, you are stuck if you lose traction on one front, AND one rear wheel. With the third open diff in the middle, you are stuck if you lose traction on ANY wheel. Those 70s FT4WD trucks were also notorious for poor highway fuel economy.

If you replace the open diff with a limited slip differential, you introduce a serious problem on ice. The break away torque for the limited slip can be high enough that it can cause the lower traction axle to skid or spin, losing traction and steering (front) / stability (rear).

The solution to this is the viscious drive found on modern AWD vehicles. This is a fairly modern inovation. It also becomes bulkier and heavier in proportion to the vehicle weight. such a drive system works well on hard-surfaced roads, and OK in snow. Deep sand, mud, or rock crawling where one wheel might be off the ground are another matter. In those cases, a completely locked driveline is near optimal, so a viscious drive would need some means to lock it totally.

The second problem is the joints used at the front steering connection. There is one type of joint that drives smoothly when in a turn, and can operate at the extreme angles required, and fit the available space. This is known as a Birfield joint. They are used on all FWD and AWD passenger cars. (usually referred to as CV joints, but the Birfield is only one type of CV joint) They are also used on the front end of Toyota part-time 4WD mid-sized trucks (Tundras I don’t know about).

The Birfield joints are just adiquate in the Toyota mid-sized applications. When they are modified with larger tires, and lower gears, it is not uncommon for these joints to fail spectacularly. Birfield eliminator kits are thus something available to the rock-crawling Toyota enthusiast.

The Birfield joints also limit steering lock a bit. Not too badly on a short wheel-based land-cruiser, but a bit annoying on an extra-cab Tacoma. On a longer full sized truck, however, this results in an unacceptably long turning radius. Note that full sized pickup chassis are designed with ONE front driveline to work on all wheel-bases from conventioal cab, to extended (4 door) cab with 8’ bed. To obtain adiquate strength, and steering lock, full-sized trucks use simple single-cardin joints (AKA U-joints) at the front wheels.

These have the undesireable characteristic of requiring the drive line to change speed twice per revolution, resulting in steering wheel shimmy, and extra front driveline wear. This is deemed acceptable in part-time service, and causes few problems at low speeds on surfaces with challenging traction. It would be annoying, and a reliabity issue if used routinely on hard surfaced roads however.

The design intent with AWD systems is to provide improved dry-pavement spin resistance, and improved safety in snow/ice conditions. The design intent with 4WD trucks is to avoid getting stuck in heavy mud or sand, or extreamly rough terrain. While there is some overlap, these goals are not completely compatable.

5

My (still being used as a plow truck) '76 Chevy 1/2 has a sort of full time ‘AWD’. It runs an open diff transfer case UNTIL you deceid to lock it in (no locking hubs, this is done in the cab). Oddly, when you lock the diff, it’s called ‘full time’.

6

Traditionally 4WD has high and low settings, and other than that traditional, full-time 4WD and traditional AWD are the same. The “fancy” AWD drive systems really aren’t “traditional” AWD; they distribute torque as needed, i.e., you’re not always in 4WD mode.

So, given that we’re talking terminology here, my Expedition had automatic 4WD which is what you’re looking for when talking AWD, but was also selectable for full-time time 4WD high and low. I’m positive that the F-series have the same thing, and they’ve probably even changed the label now because everyone wants to see “AWD” thinking it’s something special.

Here’s a good description of the differences that effectively fills in the holes in my statements above.

7

All of the F150s I’ve seen with 4WD have a selector (either manual shifter on the floor or a dial switch on the dashboard) with 2WD, 4WD Hi and 4WD Lo; they’ve cautioned that 4WD is not for use on dry pavement so I’m pretty sure it’s traditional 4WD.

8

When I bought my Cherokee I had a choice of two 4WD options. I chose the less expensive one because I would only be using 4WD in certain conditions. It is not for use on dry pavement. However the more expensive unit could be left on all the time, if desired.

9

Well, so much for being positive. I just figured that if the Expedition had it, then the F’s would, too. FWIW, you shouldn’t drive the Expedition too much on dry pavement in 4WD, either. That’s what the A4WD mode is for, which the F’s apparently miss. Now I feel bad for the OP, which it turns out is you. So, given that, I join you in your quest.

Of course on the other hand, some quick Googlefoo results in plenty of “f150 A4WD” results, so maybe it’s just an option? It’s something I should probably know, in any case.

I will say, though, that Stranger On A Train’s reasoning can’t be 100% correct, since there’s nothing really ingenious about one system over the other, and I see lots of links. Perhaps AWD is for pansy little cars, and A4WD is for big macho trucks? You don’t want to look like a safety-conscious little twerp in your hulking truck, after all.

10

My new Pathfinder does not have a ‘dry pavement’ type 4x4. It’s an off road model. I think the Limited model does have AWD, but maybe not low-range.

It does have limited slip/posi traction on all 4 wheels though. And VDC. Controled by the anti-loc brakes. Jury is still out on how well it works, but it sounds like a good approach to me.

It seems to me that vehicles that are likely to be put under more abuse have the straight up 4x4 with low range.

11

Full time, traction-sharing All Wheel Drive systems are significantly more complex than the 4WD systems typically found on trucks. Kevbo’s extensive summary (good work, there) indicates why; an AWD system on a truck that is adequate for dry pavement either requires significant compromises to its ability to go over rough, terrain, costs and weights more, or is more delicate (or a combination thereof). I still think that advances in powertrain development would let you design a true AWD for dry pavement and off-road use, but save for specialty vehicles like the HMMVV (which, as Kevbo indicates, has known problems with its CV joints due to the extreme angle and loading they are put to) there isn’t a lot of need for crossover.

Stranger

12

Bit of a bummer, that. I don’t have any particular desire to go off-roading, the worst conditions that I’ve driven in have involved heavy snow, ice and rain - shovelling out from under three feet of snow or stopping to put on chains is a pain (although it has made me a nice, save conservative driver - 4WD/AWD <> “Anti Gravity Drive”). An unloaded RWD pickup in snow can be exciting (even though I throw some sandbags over the rear axle when I head to the mountains). I really like the utility of the pickup (moving 4x8 sheets of building material, etc) and the extra couple of inches ground clearance has been handy many times.

I can understand the cost/complexity issues for auto manufacturers, it’d just be nice if they’d build the vehicles to match the driving habits of most folks - a few years ago I read that 95% of 4WD vehicles are never driven in conditions requiring 4WD. Oh well, that gets into GD/IMHO territory.

13

Well, if you notice, most “4WD” SUVs–whether the manufacturer specifically designates it as a crossover or not–are designed strictly for on-pavement, or at best lighly maintained road use. I wouldn’t go taking any of those BMW or Mercedes SUVs off road (the Porsche/VW might get further, though) and the Japanese light SUVs (CR-V, Forester, RAV-4) are really just a new evolution of the minivan. There are a few semi-practical cargo-carrying AWD vehicles (Subaru Baja comes to mind), but they strike me as being unsatisfactory compromises and ugly to boot. I, too, wish someone would make at least a light truck with a tight, modern automotive suspension, low c.g., good clearance, adequate external cargo capacity for hauling a sheet of plywood or an appliance, and AWD suitable for on-road use. I don’t know of one that really fits the bill, though.

Stranger

14

When I was looking for a new SUV, I considered the newer Grand Jeep. My Wife has an ’02 and has solid axles and does well in deep snow. But, it and Grand Jeeps in general continue to have brake problems. Among other things.

I rented a new Grand on one of our trips. And frankly, did not like it near as much as my Wife’s ’02. It’s smaller inside for one thing.

So, as a fan of Nissans I looked closer at the Pathfinder again, and while the new generation is only a few years old, I liked it. That, and I was replacing a Pathfinder that did great for me.

The Toyota 4-Runner was the other choice. It was nice but did not have some features that I was really after. And it cost another 2g’s.

So what do we have… mid sized SUV wise.

The Grand Jeep and Liberty will probably do reasonably well off road and in deep snow.

The Nissan Pathfinder and X-terra.

The Toyota 4-Runner or the new F-J (which I would have looked closer at but the timing was wrong, and it’s not a full 4 door).

Nothing does everything. The Chevy Avalanche is a try at this.

I never had problems hauling water heaters, or a washer or dryer inside my old Pathfinder (the new one is a bit bigger). For plywood, I could slide it in side ways or rope it to the roof rack.

For long stuff, like 20’ pieces of PVC or copper, I used a 12’ long 2x6 and bolted it to the roof rack as a tie off point. Then just tied the pipe to the 2x6.

:shrug: For my Wife and myself, there are still some reasonably rugged mid-sized SUV’s that do the job.

15

I think the AWD system, which really is not defined well, came about as a different and newer technology which is not the truck 4wd systems, and was designed for smaller vehicles.

I couldn’t disagree more, they don’t even fit the same role. The minivan (aka soccer mom vehicle) is for hauling multiple people, these cars/suv’s you listed don’t have any more seating room then economy cars, what they do have is more cargo space, and a better drive and suspension system then economy cars. More like a light duty SUV that can get you to places most cars would have great difficulty with.

The evolution of the minivan is unquestionably 2WD full size SUV’s and 4WD ones that will never see a dirt road.