Sliding sideways in a pickup

[James86004]

We took the Chevy out to Ajax Mine near Florence, AZ yesterday. The truck is bone stock right down to the tires, the only modification I did was to remove the front spoiler.

We noticed a characteristic that I can't quite explain. When traversing a slope where we are tilted sideways, the rear wheels really want to slide laterally down hill. It is a real issue when you are trying to get past a washout. You have enough room to get by as long as the rear wheels track behind the fronts, but they would silde down sideways a foot for every few feet of forward motion.

Is this sliding due to the weight distribution? The lighter end is not grabbing the gravel as well as the heavy end? Or is it some sort of characteristic with the suspension, something to do with roll centers? Would better tires help?

We have gotten used to it now, but it does have the effect of making the truck wider on some obstacles.

 

[viter]

We took the Chevy out to Ajax Mine near Florence, AZ yesterday. The truck is bone stock right down to the tires, the only modification I did was to remove the front spoiler.

We noticed a characteristic that I can't quite explain. When traversing a slope where we are tilted sideways, the rear wheels really want to slide laterally down hill. It is a real issue when you are trying to get past a washout. You have enough room to get by as long as the rear wheels track behind the fronts, but they would silde down sideways a foot for every few feet of forward motion.

Is this sliding due to the weight distribution? The lighter end is not grabbing the gravel as well as the heavy end? Or is it some sort of characteristic with the suspension, something to do with roll centers? Would better tires help?

We have gotten used to it now, but it does have the effect of making the truck wider on some obstacles.

you are right - it's about weight distribution, if you put more weight over the rear of the truck the back will not slide so easily. tire choice will make some difference too, but that would depend on what surface you are sliding on - loose dirt or mud or snow. if it's mud then mud tires will resist sliding better, but if it's dry, hard packed dirt or gravel then mud tires would not be any better, I think.

that must be one hell of a slope you are driving on btw.

 

[James86004]

Thanks.

Unfortunately, we weren't taking any photos, but it was not too much of a side slope. It was rocky, with loose stones, which I suppose act a little like ball bearings under the tires.

 

[lowenbrau]

What's the air pressure like? Your tires should really be inflated appropriately to the load they are carrying. Putting 80 PSI in the rear tires of an unladen pickup, just because that's what's marked on them is a mistake. Even tire shops do it though.

 

[kjp1969]

It sounds like its all about the "friction circle" of your tires, if you know the concept. I've had a similar sensation in Joshua Tree driving up a graded gravel road in our 2wd Sequoia- the rear end felt like it was sliding all over the place. It just couldn't get traction on the gravel surface, and was "power sliding" all over the place. At a slower speed, or with different weight distribution, or less tire pressure, it might have been reduced or eliminated.

 

[James86004]

What's the air pressure like? Your tires should really be inflated appropriately to the load they are carrying. Putting 80 PSI in the rear tires of an unladen pickup, just because that's what's marked on them is a mistake. Even tire shops do it though.

Tire shops are horrible about that. The university Motor Pool trucks always have 80 psi in them - I never notice until I get on the dirt road.

I had about 30 psi in them. I should have lowered the pressure for this part - I think that would have made a difference. I wish I had thought of that.

 

[James86004]

It sounds like its all about the "friction circle" of your tires, if you know the concept. I've had a similar sensation in Joshua Tree driving up a graded gravel road in our 2wd Sequoia- the rear end felt like it was sliding all over the place. It just couldn't get traction on the gravel surface, and was "power sliding" all over the place. At a slower speed, or with different weight distribution, or less tire pressure, it might have been reduced or eliminated.

It is amazing the transformation 4wd makes. We have guys driving up the mountain in 2wd because they don't "need" to put it in 4wd. They complain about how it slides all over the place on the washboardy climb. If I can convince them to put it in 4wd, they are amazed at how much the handling improves.

I am of the "put it in 4wd as soon as you can" school, rather than the "wait until I'm stuck" one.

 

[ejstavemtcnet]

Its all weight. Being an Iowa boy and having driven into my share of ditches and gravel pits over the years I know, trust me. My suburban never had this problem, but a pickup with no load in the bed, has worthless traction upgrade at an angle. Its worse if you have limited slip or a locker. The truck will naturally want to point straight up the grade because most of the weight is over the front wheels. My 2005 2500hd Chevy Crew Cab was the same way. Once the Locker kicks in, thats it. The fiberglass topper, and other weight in the back along with mud terrain tires straightened that problem right out.