Reducing "Tractor Trailer Push" E-350 Class C

[drumz]

Hey Guys:
'Ol "Twenty Questions" here again!
Are there suspension "add-ons" one can install to reduce that feeling of being pushed off the road by Tractor Trailers coming up beside you? Or how about that weird shaky feeling when your driving behind a tractor trailer in it's wake? My ride's a Class C Ford E-350 Super Duty 25'.

[BruceMc]

I'll commonly draft a truck in front us, but will hold far enough back to get the tail of the turbulence where I just feel it. Too close, and any MH will wobble back and forth - no amount of suspension work will fix it. That's too close at highways speeds anyway.
Side push/pull can be mitigated with suspension upgrades, but a lot of it is simply preparing for what is coming. This took me by surprise the first time I dealt with it, but don't much pay attention these days as it has become second nature.

The ones that will get you is the side gust when coming through a highway cut in a hill. Those have scared us more than once, particularly when ending up half-way in the other lane, or worse yet, in an adjoining lane.
Skivvy check!

[j-d]

DrumZ,

You've drawn responses from some of our most thoughtful members. Adding my $.02, their idea of checking Weight, Weight Distribution, and Tire Pressures, will cost you about $10 (truck stop CAT Scale) and provide info that's essential even if you take additional measures. If you tow a vehicle or trailer, tow it with you to the scales and you'll get a separate weight for it. Again, useful. Go to the scales loaded with People, LPG, Water, and all at Stuff you take on a trip. Bring a Load to Inflation Chart and then adjust pressure right there at the service plaza. You can use Michelin's chart for any brand of tire as long as the detail numbers match. You probably have second one on the page LT225/75R16E. Just notice Front and Rear (called Single and Dual) are different, and the weights are for one Corner of the RV. Double the charted values to match the scale weights.

If you don't find at least 75-pct or so of front axle capacity in actual front axle weight, or alternatively, at least 1/3 to 40-pct of total weight on the front axle, try to shift weight by moving it forward or at least removing it from aft of the rear axle. Water and waste tanks make a big difference if you run with them full.

From there, there's Alignment. E-Series Caster and Camber are set by switching different Upper Ball Joint Bushings. Then the Toe is set. ALL TOO MANY shops set the Toe on Ford Vans and Chassis, collect their bill, and call it good. NOT SO! You need that Caster and Camber set, and set to specs proven good for RV's. Particularly the CASTER. Shops want to set to mid-range of +3* and a Class C needs +5* or more Left, and +5.5* Right, to track well. Left Camber +1/4*, Right Camber 0*, and Toe slightly IN, like 1/8" to no more than 1/4". I'm told installing a Safe-T-Plus steering centering/stabilizing device in place of the OEM shock absorber on the steering linkage, will accomplish about the same as adjusting Caster.

I didn't catch the Model Year of your Chassis, but an E350 may not have a rear sway bar. If it doesn't, Hellwig sells a kit to add one. Many of their kits replace one that's already there. The one you're looking for has brackets with clamps that look like muffler clamps. A rear sway bar, or a bigger replacement for an OEM one, WILL help with tracking and handling.

So will an upgraded Front Sway Bar. So will a Rear Track Bar, but I'm trying to list the big hitters first:

Weight, Tire Pressure, Loading
Alignment
Add/Upgrade Rear Sway Bar

Then, perhaps, Front Sway Bar, Safe-T-Plus (Class C uses 31-140 plus a bracket kit), Rear Track Bar

[Tyler0215]

Shakey feeling behind a truck? YOUR TOO CLOSE!

[pianotuna]

Hi,

Air Tabs help.

They also reduce wind noise inside the RV.

They save some fuel--especially if you have a tail wind.

[Desert_Captain]

I've put 35,000+ miles on our 24' E-350 Class C over the last 3+ years. Our Nexus is one of the largest 24' C's out there at 101" wide and 11'4" high with a full 7' of headroom throughout the coach. I've never had a problem with trucks passing even in windy conditions. Up to 35 mph relaxed one handed steering is the norm.

Several factors make this possible starting with the proper tire inflation based upon the load they are carrying. I run my 11,500# GVWR with Michelin LTX M/S 2's at 65 psi on the rears and 60 on the fronts. Over inflating the fronts will reduce your contact patch reducing control.

Also, as noted above correct alignment is crucial. I can literally let go of the wheel{yes, I keep my hand hovering close by}, on just about any interstate or 2 lane highway and the coach will track straight as an arrow every time. After 25,000+ miles on my Michelin's they look almost new with absolutely no un even wear.

Proper loading of the coach, specifically keeping excess weight off of the rear will help. A trip to the scale fully loaded as you normally travel will tell the tale. If the front end is too light the steering will be loose.

After 30,000 miles the original shocks were shot. I didn't realize how bad they had gotten until I replaced them with a set of heavy duty Bilstein's... Wow! What a difference. Since I normally run at or near my GVWR{lots of tools and toys}, and often tow my Harley {bike and trailer weigh 900#}, the folks at Bilstein recommended the heavy duty models and the ride quality is off the chart.

To the OP I recommend several things before you start spending the kids college fund on after market junk... keeping mind that replacing shocks is just sensible maintenance and if you must spend some serious dollars start with quality shocks like Bilstein or Koni.

Get your rig weighed and adjust as necessary to balance your load. Air up your tires based upon the manufacturers load/inflation tables {ignore any sticker found in the coach}, based upon the proper load that each tire is actually carrying and last, get your alignment checked and corrected as needed.

The key is not to be surprised when an 18 wheeler comes roaring by at 80, and out here in the southwest they do that all the time. Watch your left mirror and anticipate their passing. If you are startled by their initial bow wave chances are you may over react making corrections that are not necessary. Properly set up your coach should be able to continue tracking in your lane
as the trucks pass with minimal, if any, correction/steering input by the driver. Works for me.

As always.... Opinions and YMMV

:C

[klutchdust]

Heavy duty sway bars, bilstein shocks and wheel alignment did it for my 30Ft. Cambria. Also that teeth grinding pounding when going over tracks or bumps is minimal. If you buy cheap shocks nothing will change, based on what I have read on these forums. Also air pressure, keep after that.

[DrewE]

I think it would be a reasonable idea to do basic checks of the weight balance and alignment of the motorhome. If there's not sufficient weight on the front axle, it can make for comparatively squirrelly handling; so can insufficient caster. Correcting these problems, if they exist, will make the motorhome more stable in general, including when there are crosswinds from trucks or whatever. Some suspension improvements (better anti-roll bar, for instance) might also lessen some of the difficulties.

To some extent, you just have to deal with these things. Driving a high, long vehicle with many times the cross-sectional area of a car will result in a greater sensitivity to side winds because you have a much larger sail, as it were, to catch them. If you have a relatively long overhang behind the rear axle that will also not help things any. There's a lot to be said for slowing down in situations where you encounter side winds, and being prepared to compensate appropriately with the steering.

evanrem wrote:
Wind behind a trailer might be tough to correct. Suck from passing semis can be adjusted I have found with my hitch setup. I use a pro pride and I have got it down to almost nothing on passing semis mainly by adjusting tongue weight. Picked up a new trailer this weekend and the suck was bad. Kept tweaking it and it got better still a bit more to dial it in.

While that's quite true and good advice when towing, it's not really applicable to the OP's class C (and they did not indicate they were towing a trailer with it).

[Sam_Spade]

Little to nothing you can do with a C I think.
Same thing happens to a lesser extent with a big box truck (in place of the RV).

Only seems to be a problem when you are PASSED by a big truck going in the same direction at a substantial difference in speed.....say 10 MPH or more.
One way to minimize the problem is to try and keep up with the flow of traffic a bit better.
More miles of experience and keeping an eye on the mirrors so you don't get surprised from behind will probably make things better too.

[evanrem]

Wind behind a trailer might be tough to correct. Suck from passing semis can be adjusted I have found with my hitch setup. I use a pro pride and I have got it down to almost nothing on passing semis mainly by adjusting tongue weight. Picked up a new trailer this weekend and the suck was bad. Kept tweaking it and it got better still a bit more to dial it in.

[Ivylog]

When the wind off the truck hits the back of the trailer it's going to push you further away and then it will bring you back when the air hits the front of the trailer. The best thing to do is nothing assuming there is enough pavement to stay on the road when he pushes you away as he's going to bring you back.

You are too close if you are feeling where the air comes back together behind the truck.

[srx-6]

Lots of folks like "Airtabs"