Big truck passing

When an 18-wheeler overtakes your RV, the bow-wave hits the left rear of the coach first, and that pushes the rear toward the shoulder. When the body rear moves right slightly before the rear axle does, it amplifies the push to the left that you feel in the front causing you to correct by steering to the right.

As the 18-wheeler bow wave moves toward the front of the coach, it pushes the front of the coach to the right, and when the body moves right slightly before the front axle does, it amplifies the steering correction you have already done causing you to have to correct to the left. This whole thing, if you are not used to the feelings, can be quite scary.

One way to overcome that is to install Vortex Generators like Air Tabs

They cut down on the dead air and drag on the rear of RV and greatly reduce the bow wave of passing trucks.

I installed them on my Class C and now I do not get any push from passing trucks and it greatly helped in cross winds,hardly a bobble.

I would guess you have some roll steer and could benefit from adding front and rear sway bars.
Anyway have your suspension checked.

If you haven't heard about the Cheap Handling Fix, do a google search and read about it. See if it applies to you. We did front and rear on our F53 chassis and it made a big difference.

How old is your TT or 5thW? I had a 9 year old TT. I was pushed around at highway speeds by trucks. I upgraded the suspension which made all the difference in the world. It had the OEM plastic bushings that were worn out and dry! Went to wet bolts and bronze bushings, and Dexter E-Z Flex equalizers. This tighten up the suspension and reduced the sway.
This worked for me and may not be the answer for others.

Big rigs push lots of air around and sideways,upseting every vehicle they pass,
IF all rigs and Motor homes were aearodynamic like this bus youd never feel it,at least thats what the owner says

57 flexible bus

Yup, normal, and what they said. I feel that the speed diffrence between the two make it more pronounced. So, if the truck is going faster then you it moves you more.

The air coming off the passing vehicle adds new side forces to the vehicle being passed.

In a one unit RV such as a motorhome, it is mainly pushing toward the right. As you watch the mirrors just as the truck gets even with your back bumper, hold the wheel and be prepared for a very small correction to counteract that force.

In a two unit RV such as a 5er or TT, that unit is pushed toward the right also. The pivot point of the unit - the hitch, is pushed toward the left. RV combos with the hitch mounted over the real axle have the least movement because the angle of the push is minimal. Rigs like my truck can get a substantial push toward the left.

I have to be prepare when being passed to turn toward the right a little.

The number of things which can affect the force are huge. Basically a lot to do with aerodynamics, speed differential, and speed of the vehicle being passed.

RVs are NOT aerodynamic, and the faster they go, the more they are subject to forces exerted upon the RV. As mentioned above, a movement at 70 will feel massive, at 60 much less. In MOST cases.

Every passing is a bit different, and it takes miles of driving to understand your vehicle's sweet spot.

MickUpi wrote:
I done several searches on the following topic but could not find anything on it. I am usually driving in the right lane on the interstate or a four lane road. When a big truck passes an the left as it gets about even with me our rig is pushed to the right. It's usually just slight but sometimes it be a fairly hard push. It's only scared me once on a US highway. It happened right as I and the truck driver crossed a bridge. After a rather strong push I am estimating the side of our MH was less than a foot from the bridge and it was a bit scary. Some big trucks don't blow our MH at all. I'm not sure what's up with that. Our MH is 28 feet long and 11 feet 7 inches high. I have noticed bridges on US highways can be much more narrow than on interstates.

Mine does the opposite on the interstate. I used to pull a heavier trailer without WDH or sway control so it the push away from the passing truck was felt in the tow vehicle. Now with out new unit and WDH / SWAY I feel the tow vehicle get pulled toward the passing truck. I found that towing at 65 instead of 70 greatly reduced this feeling and at 60 it's barely noticeable.

Ever watch NASCAR....side drafting can create lots of issues

Bridges are only narrower due to lack of shoulder. Lanes don't get narrower