Originally Posted by eason
P.S.- also i tow a 2015 jeep rubicon 4 door which can feel at times like the tail wagging the dog.
Okay, let's see… A Jeep Wrangler Unlimited Rubicon has a GVWR of 5700 pounds, in excess of a Grand Tour's towing capacity. The curb weight is 4500 pounds, so if you're carrying any cargo more than than a full tank of fuel in it (fuel is considered part of curb weight) you're pushing the limit of your Grand Tour's towing capacity.
The Jeep has a very boxy shape, and is long enough that it doesn't fit entirely within your Interstate's slipstream. Meaning that the rear end of the Jeep is always in turbulent air. That would certainly contribute to the "tail wagging the dog" syndrome you mentioned.
One thing that should
help is to get a front-end alignment done on the Grand Tour, especially if you haven't done one since buying the van. When Airstream bought the vans from Mercedes, the empty vans had the correct alignment. But that's before Airstream added a bunch of weight that may or may not be a balanced load. And Airstream does not do alignments on the vans they sell. Since a bad alignment can contribute to directional instability, getting the van realigned is pretty much the first step toward a fix, and is cheaper than other suspension improvements you could try.
From a safety standpoint, there are two "best practices" for high crosswind situations. (1) Park it and wait for the wind to die down; and (2) if you have a second driver with you, unhitch and drive each vehicle separately until the winds die down. Each vehicle by itself will be better-behaved in a crosswind than will the combination hitched together.
Given the shape of a Jeep and the shape of a Sprinter, each one will catch crosswinds more strongly at the rear of the vehicle than at the front, and they will both have a tendency to want to weathervane (point up into the wind), meaning the rear will want to veer farther than the front and steering corrections are not too difficult or scary because the van will actually help you steer in the direction you want to go.
Pin the two vehicles together at the towbar and it no longer becomes possible to predict how the combination will react to crosswinds without putting them into a wind tunnel and/or on a skidpad, but I'm thinking the Jeep will be more stable than the Sprinter because of having no overhangs to speak of, and having less surface area to catch the wind. That means the rear of the van will veer less than the front if both vehicles catch a crosswind (the exact opposite of weathervaning) as the Jeep serves as an anchor, and you need more
steering correction to stay in your lane; the van will have a tendency to fight your steering corrections.
Ballasting by filling the fluid tanks and emptying the overhead lockers will not help much, except to reduce the tendency of the van to roll over as it veers. Suspension improvements other than the front-end alignment are the same. If you upgrade the rear suspension the van will not rock or lean and much as it veers, but that won't keep a crosswind from making the van veer out of its lane because you're still at the mercy of the van's surface area acting as a sail.
I have not crunched numbers on this, so everything I said is an opinion, not an analysis. If anyone out there has a different interpretation, I'd be glad to read it.