4 Wheel Drive Question

[cvflats]

I know you are not supposed to drive on dry pavement in 4wd. I dont. I was wondering mechanically why it matters. Is it the front differential that gets abused or what? why would it matter if all 4 wheels were getting power on a dry road as compared to a wet one or a muddy trail. just curious

[2005LT]

Someone can correct me if I'm wrong on this. I have heard its because of a slight difference in speed between the front and rear wheels. If the front is trying to pull either faster or slower than the rear, it increases frictional wear on the components and possibly more heat I believe this is why you are supposed to shut off 4x4 on dry pavement for long distances and high speeds. Probably better explanations out there.

 

*edit: and the extra friction and such lowers fuel economy too.

[fbachman]

I am not an expert, but I can tell you my supposition...

 

When a truck makes a turn, or maneuvers in any way, each wheel is turning at a (slightly)different velocity.

 

In 2WD mode, the rear wheels compensate for this by virtue of the differential which has structures in it to allow for the wheels to turn at different velocities while under power. In this circumstance, the front wheels don't matter, as they are turning free (relative to one another), i.e. not turning under power.

 

Now, in 4WD, all four wheels are forced to turn at the velocity commanded by the drivetrain/transmission taking into account any reduction by the transfer case/transmission.

 

When you attempt a turn on dry pavement under 4WD for example, the front wheels WANT to turn at different velocities, but are hindered from doing so because of drivetrain input and the large amount of traction between the tire and dry pavement. It puts a tremendous amount of strain on the drivetrain. On snow, for example, as the traction between the tires and the ground tends to be less, the tires can slip a little and relax the transmission of the mis-matched wheel speed stresses directly through the drivetrain.

 

In 4WD, for example, on dry pavement, if you execute a tight turn, you get wheel chatter and hop because of this phenomenon. Loads of stress on the drivetrain.

 

That's probably why. There may be other issues I am overlooking, but I think that's the biggie.

[Sir Dan]

We always called it "buckling" when a 4x4 would hop around a corner. It does have something to do with slightly different gear ratios front to back and can be damaging if it happens often to the newer drivetrains, which aren't nearly as robust as older trucks. My dad use to tell stories about some of the the old 4x4's that if you locked in the front end on dry pavement and even drove straight down the road, the front end would start to bind up. Back then the 4WD was only used to get you out of a tight spot, not keep you on the freeway going 75 when the roads get icy and snowy.

[sc4808]

It is simply because when you turn, the front of the vehicle takes a longer path than the rear, get on dirt somewhere and make a few hard turns, and then get out an look at your tire tracks in the dirt, the rear tires do not follow in the same tracks as the front and are taking the shorter path which means that they make slightly less revolutions that the front wheels do.

 

When in 4wd the front and rear axles are locked together mechanically, when you make a hard turn on a dry surface, it puts tremendous stress on the transfer case and can do serious damage, most of the time with stock tires you will just hear the front tires chirp or hop to release the stress, but if the truck is heavily loaded or you have larger tires, it is possible to break the transfer case housing.

 

This is not an issue on surfaces with poor traction, since the tires will simply slip.

 

It is NOT because of a difference in gear ratio front and rear.

[AKBlue]

I may have missed someone else that brought this up...

 

but to my knowledge the largest issue is that fact that when the front wheels are traveling in a turn, the outside wheel is turning faster than the inside wheel, thus causing the binding in the front axel. That is the reason the tires lurch...they are trying to equalize.

[stingraydave]

The Push Button 4wd (Auto-Tracs) also have clutches that drive the front end in the transfer case and I suspect it would cause alot of wear on them as well.

[085300]

My mother drove 60 miles in her 2002 GMC Yukon in 4 Low at highway speeds on dry tar, lmao. She like It sounds different, I'm yea no sh!t!!! No damage done though.

[gvbhunt]

Main reason, regular 4wd I do not believe has a center differential, but AWD does. When you make a tight turn the front two tires turn different speeds than each other. The rear two tires turn different speeds than each other and the driveshaft has to turn different speeds for both the front and the back. Basically all 4 tires have to turn at different speeds.

[jrrod2004]

My mother drove 60 miles in her 2002 GMC Yukon in 4 Low at highway speeds on dry tar, lmao. She like It sounds different, I'm yea no sh!t!!! No damage done though.

 

 

she was in 4LOW...at highway speeds...??? Fastest I ever drove with 4LOW was 19 MPH and by then the engine was nearing 4500 RPMS...

[DBVille]

Four Wheel Drive (4WD), not AWD, does NOT have a center differential. The front axle and the rear axles have differentials that work side-side ONLY. So, anytime 4WD is engaged, and you turn (as previously pointed out), the front tires scribe a longer path, a larger circle. But, they are both turning at the same speed, since there is not an active center differential. So, something has to give.

 

What gives is the tires - they end up sliding on the ground. On dirt or low friction surfaces, no big deal. On pavement, the tires don't slide readily, and a lot of forces buildup in the drivetrain until a tire slips enough. This causes the groaning noises you hear. It is not good for the tires or the drivetrain, due to the forces involved.

 

The front axle or different speeds of the front (or rear) tires alone is NOT an issue. It is the speed difference between the front and rear axles.

[Rons05z71]

Its all about the wheel speed between the left and right tire

[DBVille]

 

 

Its all about the wheel speed between the left and right tire

Nope. The left and right tires have a differential between them. It allows them to turn at different speeds. Its all about the front and rear axles. In 4WD, there is no differential, and during turns, the front and rear axles have to turn at different speeds!! The front tires take a longer path, and have to turn faster than the rear tires. While the outside tirer turns faster than the inside tires, the issue is the lack of differential between the front and rear axles.

[bubba33]

My mother drove 60 miles in her 2002 GMC Yukon in 4 Low at highway speeds on dry tar, lmao. She like It sounds different, I'm yea no sh!t!!! No damage done though.

 

 

she was in 4LOW...at highway speeds...??? Fastest I ever drove with 4LOW was 19 MPH and by then the engine was nearing 4500 RPMS...

 

 

Ya theres noway in hell that she drove it in 4LOW at highway speed.

[VMax2007]

Its all about the wheel speed between the left and right tire

Nope. The left and right tires have a differential between them. It allows them to turn at different speeds. Its all about the front and rear axles. In 4WD, there is no differential, and during turns, the front and rear axles have to turn at different speeds!! The front tires take a longer path, and have to turn faster than the rear tires. While the outside tirer turns faster than the inside tires, the issue is the lack of differential between the front and rear axles.

 

 

:Werd: