Anyone know the cause and cure of the F250 side skitter?
Hitting bumps on a curve can be a real sphincter tightener. If you don't jump to correct, the truck rights itself quickly. Some sand bags in the bed don't help much. I can't tell whether it's a primarily front or rear end issue. It is probably not tire inflation, as other similar vehicles won't skitter with 80 lbs in the rear. I assume it's the same for gas F250s, the only difference being a heavier snout in diesels. On the other hand, the F250 does less "tramlining", following grooves in the road that take you where you don't want to go.
Wondering about:
--lousy stock shocks
--inherent in leaf springs (not noticed with GM though)
--frame shudder
--too much tires pressure for the load
--too fast for road conditions?

 

I know what you're talking about. It happens when there is lateral g force on the vehicle, the rear axle is launched upward because of a bump (or there is a sudden change in the road surface where the road drops a couple inches away from the tires) and in the time it takes the tires to land back on the ground the truck has moves laterally a couple inches.

So, when the tires aren't touching the road, the truck moves sideways a couple inches.

This means that we need to find a way to get the tires to move downward faster.

Shocks actually resist axle movement and a good stiff shock will actually make the issue worse. Shock ensure that the axle moves up and down slowly.

Springs keep the axle pressed against the road surface and react fast enough to handle the road situations.

My opinion (and I've tried to figure this problem out for a long time) is that due to the weight of the axle, wheels, and tires, there is simply too much mass involved for quick enough action to fix this issue.

I think it's called "unsprung weight", meaning the mass of the components is not supported by the leaf springs. Less unsprung weight is ideal, more of it moves toward the less desirable. It's just the nature of a heavy live axle leaf spring configuration. Nature of the beast.

Perhaps the issue did not arise in your previous trucks because they weren't as heavy.

I do believe that lower tire pressure helps a lot, reduces the super ball effect of high psi tires. (Ever take a wheel of your truck and bounce the tire? It rebounds HARD, like a tennis ball on steroids)

Sorry for the long post but I've been thinking about this for a long time.

 

I have a 2011 diesel and have Toyo open country A/T tires E rated. I experience the same thing. I keep the tires between 75-80 psi. and the bounce is very defined without a load. But if I'm running at about 65 psi not so much but still there.

 

This is the norm. My 350 does it even with Bilstein 5100's and aired down tires at 65psi. A 7k rated axle with an empty bed over it weighing less than half of that is going to be a bit rigid.

 

Bottom line these trucks are made for hauling not running around empty. A soft ride would mean little or no payload.

 

I know it's normal but it is absent in the Ram and GM 2500s (which have their own issues, my GM would bounce so much the ABSwould activate while going straight!) I think the unsprung wt issue is key. Really appreciate your thoughtful post ruschejj. I had only thought of unsprung wt as it applies to sports cars. Huge issue there. A few pounds per corner can win races. Theoretically then the bounce should be better with smaller wheels and hollow axles? The F250 always rights itself but someday my wife will panic or my hand will slip (due to the bump) at the wrong time and.. trouble trouble. Imagine the lateral loads after the wheel lands, much higher than at "takeoff". It never goes off course though, weird.

 

I'm going to add that having solid axles both front and rear contribute to this a lot more than say the IFS on the GM products

But rusche, I'll counter your shock theory by saying that a stiffer shock, or at least better valved to suit the springs on the truck, would do a better job of keeping the springs from kicking up so fast so high, off of the road, in other words, when a bump is encountered.

Could help reduce some of that loss of contact with the road.....

Also- a better steering damper would help keep the front end from "kicking" so much when the wheels are turned while hitting bumps in the road. In other words, I'm sure there are ways we can reduce or lessen the affect, but I don't think it's possible to eliminate it entirely, due to the truck's design (due to its intended use)

 

I've had this happen to me on many trucks. Usually do to poor rear shocks. But even with million dollar shocks, I don't believe it would be TOTALLY eliminated.

 

I have the same issue too. Lower PSI tires and adjustable shocks have made a bit of a difference for me.

 

I have seen this problem for many years now and find that the problem is magnified considerably with wash boarded gravel/dirt roads and especially going up hill. Weight in the truck helps a lot. Air pressure in the tires helps, but is a pain to re-inflate for a long run home on the highway. Speed helps: visualize picking a particular speed for the road section such that the wheel bounce always comes down on the top of the wash board. It is a lot smoother than just a little bit slower or a little bit faster speeds (harmonics). And at slower speeds using 4x4H on the gravel usually helps in that one axle is is pulling while the other is bouncing and therefore reduces the bounce. These last two help with the "un-sprung weight" issue mentioned previously. On asphalt, I keep my tires inflated correctly, the shocks in good condition and know the road, if possible. There is a section of 65 mph freeway off ramp near here that some idiot decided to grind out rumble strips across the lane ON a 30 mph turn! A sphincter activation experience!

 

You don't have to be on a curve to skidder. A bad washboard can walk a vehicle right off the road.
You don't have to be in a Super Duty to skidder. Although from my experience, trucks seem to succumb more easily.

 

I had a 2000 Dodge Dakota crew cab with 5.9 V8 and trailer tow package that did the same thing. My 2004 F250 6.0 cc/srw with the trailer tow package was very stable during a long sweeping turn at highway speeds. My 2014 F250 crew cab with the tow package has this tendency to 'skitter' (didn't know there was a term for this) and it is very discomforting when the rear of the vehicle jumps sideways, especially when you're traveling at highway speeds.
Randy

 

Jwp, next time it rains, or, if you have snow/ice, find a parking lot and test out the vehicle stability systems on the truck. There are 2 I think, traction control and stability control. You should (we all should) know how these systems react when we are in a safe environment so you'll know what's going on.

First thing I can say is, it's nearly impossible to create wheel spin in straight line acceleration.

Next, when it's slick roads, it's very hard to get the rear end to kick out. We can't drift, slide, do donuts, whatever you may want to try. The stability control works very well and it feels weird when it kicks in.

Both systems have lights that blink on the dash when they take over the vehicle.

I used to enjoy the "loose" rear end on these trucks (any rear wheel driven car too) but the nanny systems now make it real hard to get frisky.

There's a section of I-10 in Louisiana where it splits, south to New Orleans, west to Baton Rouge, and the ramps there must have 4 inch drops for every expansion joint. My rear end hops all over the place every time I drive through there. I think that's the worst place I can think of for experiencing this skitter stuff.

 

I think it's related to ABS, or traction control.
My '02 E350 15 passenger V10 does it, even when crossing a small access plate in the street.
My '72 E300 Supervan did it but I think that was related to the front end.
It would begin a shimmy, if I hit something small.

 

We have some really bad expansion joints around here and even moving in a straight line and holding a steady speed, my truck would almost change lanes if I wasn't prepared for it. The backend would literally move several inches out of line with the front end. I purchased and installed quality shocks and replaced the factory ones - not really expecting to see much difference, but I was wrong. The difference was huge.