Highway 4wd low

[Craig0320]

Brother would be walking! WITH CRUTCHES!

FIFY

 

[97RangerXLT]

Not sure if this helps, or just makes it all more confusing, but my theory is that a greater weight load on a tire (or less air pressure in the tire would also create the same circumstance) does NOT change the circumference of the tire (the circumference is held firm by the steel belts in the tread, the belts cannot flex in a manner that would allow a change in circumference). What happens is the greater deformation of the tire's shape causes more squirming of the tread blocks right where the tread initially contacts the road, and then again where the tread leaves the road with each rotation. This causes more friction (and thus heat) and also has the effect of causing the tire to rotate at a speed something in between that of a non-deformed tire, and a non-deformed tire of the same radius as the deformed tire.

On the other hand, there will always be a tiny bit of give due to the flexibility of the tread blocks, even on dry pavement. It's just enough give so that things should not destroy themselves (not right away, anyway) if the truck is driven in a straight line on dry pavement in 4WD. It is not enough to allow for turns on pavement however, and this is generally where things will start to grenade.

I think this explains it best. the tire with the weight on it gets deformed, the radius is slightly shorter and because of that, the tire makes the same revolution as the non deformed one but does not go the same length on the road. so the tire "squirms" and slips just a little bit. no big deal on surfaces that can allow that tire to slip it doesnt bother the transfer case that much. but on dry pavement, that 1/4" to 1/2" of slippage is much harder to do and the tire will grip better and be harder to slip (you might even hear it chirp a bit) and cause it to put a lot of stress on the transfer case, which wants to output the same speed for both axles. each time that tire chirps or slips, it is like putting a hammer to the drive line. as you speed up, that 1/2" slippage will absolutely pound the driveshafts and gears in the transfer case, until something breaks. If you are lucky, it will be your hub or a u-joint.

AJ

 

[Ranger850]

THIS. All of this, this is most of the reason I stay with my 2wd. More moving parts to lube/fix. Who knew you had to be a freaking circumference geniuses or a gear guru to own a 4wd. I commend you all just for even knowing this stuff. I had no idea it was this complicated. If I had my druthers, I'd go with a AWD system like a Subaru, they seem to have figured that part out.

 

[ericbphoto]

You don't really have to know all that stuff. Reading the operators manual tells you what you need. It's just that most people never read that little book. Plus, occasional mistakes will happen.

 

[19Walt93]

I couldn't own a Subaru, every one I've ever heard running has a lower end knock that the owners can't hear. All the newer stuff is fussy about tire circumference differences because it affects the ABS and traction control, Ford says 3/8" circumference difference is the max allowable. We had a "customer" with a Town Car who put 4 ice radials on it then came in with traction control issues. He insisted the problem was there with the original tires. Most Lincoln owners drive smoothly, not this guy, he'd accelerate at WOT from a stop and the traction control would kick in and limit the car to 40 mph. After days of going through the TC system with a fine tooth comb, we swapped the wheels off a Crown Vic onto his car and the problem was gone. The hard acceleration was crushing the tread on the soft ice radials, effectively making the tire a smaller diameter and the traction control was kicking in because it saw the rear wheels were turning faster than the front wheels. He refused to believe me so we let him drive it with the Crown wheels for 3 days, then he grudgingly accepted the facts. He never paid for the week of labor, though, that's why he gets quotation marks around customer. One of my friends bought 2 tires from a local guy for his 04 Ranger at a "super deal". They were about 3/4" shorter than the other pair and the first time he engaged 4x4 it wouldn't disengage. He drove the rest of the way to work before the transfer case fragged. The guy who installed the wrong tires didn't feel he was responsible for the damage. He's another one of those independent mechanics who's "better than the dealer."

 

[Ranger850]

I was ONLY talking about the AWD system the Subi's have. I am not a fan of the box/flat/pancake 4's, or the exterior styling of any Subaru

 

[Shran]

AWD is arguably more complicated than a typical 4x4. You still have a transfer case or something similar plus a clutch pack or electronics that allow it to have some slip on the highway for normal driving.

 

[sgtsandman]

THIS. All of this, this is most of the reason I stay with my 2wd. More moving parts to lube/fix. Who knew you had to be a freaking circumference geniuses or a gear guru to own a 4wd. I commend you all just for even knowing this stuff. I had no idea it was this complicated. If I had my druthers, I'd go with a AWD system like a Subaru, they seem to have figured that part out.

There is still things you need to know and understand with them as well. Many of the things that effect 4X4 systems are still applicable to AWD. It really isn’t all that confusing or complicated, just more to pay attention to.

 

[alwaysFlOoReD]

It's simple....don't drive on pavement in 4x4 low.

 

[pjtoledo]

THIS. All of this, this is most of the reason I stay with my 2wd. More moving parts to lube/fix. Who knew you had to be a freaking circumference geniuses or a gear guru to own a 4wd. I commend you all just for even knowing this stuff. I had no idea it was this complicated. If I had my druthers, I'd go with a AWD system like a Subaru, they seem to have figured that part out.

AWD has been around for a while.
in the mid 70's Dana had the NP203 transfer case which had a differential allowing power to all 4 wheels.
when you wanted to break things the transfer case could be locked to put REAL POWER to all 4 wheels.
the newer systems are leaps & bounds better than the older stuff.

 

[don4331]

THIS. All of this, this is most of the reason I stay with my 2wd. More moving parts to lube/fix. Who knew you had to be a freaking circumference geniuses or a gear guru to own a 4wd. I commend you all just for even knowing this stuff. I had no idea it was this complicated. If I had my druthers, I'd go with a AWD system like a Subaru, they seem to have figured that part out.

Actually, you should be paying attention circumference even with 2wd, especially if you have limited slip - Driving 200 miles with one tire down 10psi, will wipe out the clutches.

AWD has been around for a while.
in the mid 70's Dana had the NP203 transfer case which had a differential allowing power to all 4 wheels.
when you wanted to break things the transfer case could be locked to put REAL POWER l 4 wheels.
the newe systems are leaps & bounds better than the older stuff.

Nit pick - New Process Gear wasn't a subsidiary of Dana. And is now subsidiary of Magna International.
And we pulled the NP203 into 4Hi-locked to avoid breaking things - usually meant at least 3 tires were turning (rear on the 3/4 ton had Detroit Locker).

 

[Ranger850]

AWD is arguably more complicated than a typical 4x4. You still have a transfer case or something similar plus a clutch pack or electronics that allow it to have some slip on the highway for normal driving.

There is still things you need to know and understand with them as well. Many of the things that effect 4X4 systems are still applicable to AWD. It really isn’t all that confusing or complicated, just more to pay attention to.

I can get into any Subaru in the world and put it in "D", and drive under normal conditions on Pavement or Dirt or Grass, or pretty much on any surface, and NOT worry about a transfer case exploding. I understand that, mechanically, it may (or may not) be more complicated than a true 4wd system, but to the Driver, it is much simpler.
I never said AWD was new, just that IMO Subaru has that part figured out, just like Honda has the Variable Valve Timing better than any other auto maker, just like Fords EB technology is knocking the sock off the Competitors, Just like Chevy has the best....Corvette?

 

[Shran]

I don't see how Stupidru has anything wildly different than other carmakers... my old 2000 Astro van was AWD and same deal, drop it in D and go. The AWD Grand Cherokee I had was also like that but it had a low range option.

I have nothing against them, except that they have a following which in turn makes them more expensive than I think they should be. I blame hipsters.

 

[Ranger850]

I mentioned Subaru, in particular because EVERY model that rolls of the line, is AWD. I've driven a few, very fun. Hipster crowd can be annoying for sure. But i was just saying that, for me, AWD would be the way to go to not destroy anything. It was more of an AWD vs. 4WD thing.

 

[85_Ranger4x4]

THIS. All of this, this is most of the reason I stay with my 2wd. More moving parts to lube/fix. Who knew you had to be a freaking circumference geniuses or a gear guru to own a 4wd. I commend you all just for even knowing this stuff. I had no idea it was this complicated. If I had my druthers, I'd go with a AWD system like a Subaru, they seem to have figured that part out.

Keep all tires the same size
Keep all tires correctly inflated
Don't engage 4hi unless all wheels are going the same speed
Stop and shift to neutral before engaging 4lo
Don't drive 4lo at high speeds.

That pretty much keeps you safe on a 4wd. Three of those 5 don't apply to awd and it is because AWD's shortcoming is generally the center diff doesn't lock and there is no low range.

The last one is akin to a "caution contents may be hot" warning on coffee cups.