F53 chassis hanling in the wind

I have spent a ton of years as an Engineer in the Aircraft modification business and the same ton of years owning RVs. So I have given this problem lots of thoughts. here is my take:

Background:
1) Vehicles traveling down the road have a high pressure bow wake in the front and a low pressure area in the rear.
2) the magnitude of each of these is dependent on relative air speed of the vehicle (ground speed taking into account wind direction/magnitude) and vehicle aerodynamics (shape).

Problem
1) When one vehicle overtakes another these two areas interact causing forces on the vehicles. The magnitude of the forces applied to the vehicles has to do with the magnitude of the respective high and low pressure areas.


You cannot do anything about the other guy's vehicle. Although if you notice you probably have less push/pull from a truck with skirts and tails on them. As these mitigate the low pressure areas around the truck

That leaves what can you do to your vehicle.

Reduce the forces:
1) Here is where the airtabs, vorblades, etc. come in. They reduce the low pressure area behind your vehicle, thereby reduings the forces on your vehicle from a passing truck. Other than buying a Monaco Vesta or Holiday Ramble Trip (the only Class A I know of designed with wind tunnel testing) there is not much else to do on reducing the forces.

Reduce the effect of the forces on your vehicle.
1) So you have done what you can to make your vehicle more aerodynamic and you can't affect the other guy. So the last option to to reduce how your vehicle reacts to the forces.
2) What can be done here is very vehicle dependent. It depends on the aerodynamic shape of your coach (where are the forces being applied), your chassis, vehicle loading, etc. This is why we see what works for Coach A has little effect when the owner of Coach B tries it. hence so many threads that say "this solution worked great for me" and someone replies " it did nothing for me". The best option is to find folks with the same coach and find what has worked for them to limit the effect of the forces.

For me:
1) In previous RVs I had good luck with airtabs and vorblades. However, others have not.
2) I brought a Monaca Vesta. The engineer in me got tired of trying to mitigate the effect of the problem. The vesta was the only Class A I could find where engineers actually did wind tunnel testing to design a coach that mitigated the problem vice the effects. The result is amazing. it tracks like a train and I truly do not know when a truck is passing.

My $0.02 for what it is worth....

We did the CHF both front and rear on our 36'. Also added the Saf-T-Plus on the front. It helped quite a bit, but we park it when it's windy.

Have also read on this and other forums that the shorter motorhomes do not handle as well as the larger ones. Reason ? don't know.

weighted the rv? not enough weight in the front maybe.

not for you to do the same but after weighting mine
mine has slightly more than 1/3 in the front and a bit less than 2/3 in the back. it is ok with the wind

back tire 95 psi, front 105 or 110 (not sure)

I just did the quick division of the ratio of wheelbase to overall box size and you are running and index of 48....anything below 50 is considered not safe, anything over 52 is ideal. I would be complaining to the manufacturer. Check my math...

I may have missed it, but I didn't see where you said what year model and how many miles are on the rig. When we got ours, I was very nervous about how it handled, especially the body sway. When I got under the rig, I saw that all 4 of the sway bar bushings were completely gone....not just worn, but GONE! I replaced them and it made such a significant improvement, I decided to leave the CHF alone. Since then, I have added air bags and replaced the front leaf springs as I had one that was in a negative arch and causing the rig to lean to one side. The leaf spring replacement made a very significant improvement in handling as did the air bags.

To address your problem, I would suggest making sure that the sway bar bushings are in good shape....if they are original, I would also suggest replacing them with a little stiffer poly bushing to take some slack out of the sway bar setup. Since I don't have a trac bar, I can't address that as an improvement, but many have done it and swear by it to stop the pushing you describe when the wind blows or a truck passes. Me, personally, I experience more push from a small car that I do from a big truck. It's weird, but it's what happens.

Get your alignment checked by a big truck place that knows how to align large vehicles, and set the alignment as recommended above. That will help with the rig's handling going down the road (straight-ahead tracking) and keep you from having to constantly adjust the steering to stay in the lane.

There are several other add-ons that you can purchase and install, but at the end of the day, it's never going to drive like a car. I had to resolve myself to that fact and now that I have adjusted my driving style to match that of the rig, I have a much more enjoyable experience when we travel!

That's right, there's nothing like a long wheelbase with short rear overhang, PLUS the front end loaded to the limit axle-weight spec PLUS a couple of additional degrees of front suspension caster,.....in order to realize good directional stability. Either believe in the science of it, or not.
I would first try loading the front end to its maximum load capacity of the front axle, THEN install 2-degree shims to increase the castor(that's how you adjust castor on the F-53 with leaf springs). Also, make sure the toe-in adjustment is correct. You can do all this yourself,.....I did (back when I had a Vectra on a F53 chassis.

Our new to us 32k Vista was a bucking bronco our first trip out. Did the CHF and installed Safe T Steer and it was a night and day difference improvement.

But, any cross wind at 20 MPH or more leads to white knuckles. Many have said it is the nature of the beast, a 30 foot or more brick going down the road, diesel or gas chassis. Those with tag axles seem to handle the best under these conditions per posters here on the forum.

That unit appears to have a 158" wheelbase carrying a 330" box. That has to translate to a lot of rear end hanging behind the rear axle. Sounds like a pretty significant lever for the wind to push against.

I have absolutely no experience with the Ford chassis, but I have solved the sidewind and passing 18-wheeler bow wave effects on my Workhorse W20 chassis. From what I have read about the problem and felt with my butt-dyno, the movement is made worse when the coach body and the chassis are not solidly connected to eliminate side-to-side movement. This is definitely a problem with leaf spring suspensions like on the W20.

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.

What I have found is that the best solution for the whole problem on my W20 is to install a trac-bar on both the front and rear axles to force the body and chassis to react together when needed. FYI, the sway bars on Workhorse W-Series chassis don’t help side-to-side movement at all because they are mounted only between the leaf springs, and not to the chassis.

IAMICHABOD wrote:
Another alternative is to look into Air Tabs. My RV handled very well but cross winds and passing trucks upset it quite a bit,after installing Air Tabs,cross winds and trucks are no longer a problem as it once was.

I experienced the same thing with my Workhorse chassis. For less than the cost of a tank of fuel, these may solve your problem.