Improving Diesel MH Handling in Crosswind

Preparing for a trip to Florida later this week. Over the last few weeks, I have spent time making sure that everything is set with the motorhome. Nothing major. Just replaced the house batteries. Checked the fluids. That reminds me-I still need to check the generator oil. I'm getting the tires balanced tomorrow.

I had it at a Freightliner repair shop last week to address what I thought were steering/handling issues (for example possibly loose or worn bearings). Basically, I found myself fighting the wind on a few occasions. I know that crosswinds are an issue with any high profile vehicle. They looked through everything and found nothing. Sometimes I can be a little too meticulous :-X . While I still paid for three hours of labor; at least now I have peace of mind going down the road.

What have others done to improve coach handling in crosswinds? Obviously, I will adjust my speed and use greater caution. Of course, there are other factors such as water and gas when the coach gets loaded in a few days.

Folks have used various designs of steering stabilizer to help with crosswinds. This article in our forum Library illustrates how I installed a Blue Ox steering stabilizer. Some folks have installed bi-directional stabilizers, but I don't recall the brands. Since you're laving this week, you may not have time to purchase and install something similar.

There is no single (or simple) answer to that, since it depends on why your coach is [maybe] more sensitive to crosswinds in the first place. In general, reaction to side winds decrease as the coach weight goes up, and that's why DPs tend to resist better (they are mostly heavier than even the largest gas-chassis coach).  However, their are a myriad of factors, e.g. chassis weight distribution, tire size and tread pattern, tire pressure, solid axle vs IFS, suspension parameters, highway crown or ruts, etc. etc. etc.

Worn suspension and steering is a possibility, but not real common in diesel chassis rigs simply because most DPs don't get driven enough for wear to be a factor.  Good that you checked, though.  Did they do an alignment too?  It has to go on the machine to check alignment, so a check is effectively the same as doing it.

One thing you can do is to make sure your tire pressure is optimal for the actual coach load and balance. That means getting it on a scale for at least front & rear axle weights (wheel-by-wheel preferred) and then using the tire makers load-inflation tables to fine tune.  Excessive tire pressure makes the steering react more easily to external pressures.

Some people like to add steering assist devices but I'm not a big fan of them for DPs with air suspension.  The higher end assists can be set to continuously counteract side forces, making them handy in a continuous crosswind, but not so useful in gusts. Blue Ox Tru-Center is one such.  Devices such as Safe-T-Plus and Steer Safe make some claims to help steer & handling, but in my opinion they are mostly applicable to older chassis with leaf spring suspensions.

Tom said:

Folks have used various designs of steering stabilizer to help with crosswinds. This article in our forum Library illustrates how I installed a Blue Ox steering stabilizer. Some folks have installed bi-directional stabilizers, but I don't recall the brands. Since you're laving this week, you may not have time to purchase and install something similar.

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Thanks Tom. I will check out the Blue Ox when I return. Looking forward to see how it handles on my first long trip.

Gary RV_Wizard said:

There is no single (or simple) answer to that, since it depends on why your coach is [maybe] more sensitive to crosswinds in the first place. In general, reaction to side winds decrease as the coach weight goes up, and that's why DPs tend to resist better (they are mostly heavier than even the largest gas-chassis coach).  However, their are a myriad of factors, e.g. chassis weight distribution, tire size and tread pattern, tire pressure, solid axle vs IFS, suspension parameters, highway crown or ruts, etc. etc. etc.

Worn suspension and steering is a possibility, but not real common in diesel chassis rigs simply because most DPs don't get driven enough for wear to be a factor.  Good that you checked, though.  Did they do an alignment too?  It has to go on the machine to check alignment, so a check is effectively the same as doing it.

One thing you can do is to make sure your tire pressure is optimal for the actual coach load and balance. That means getting it on a scale for at least front & rear axle weights (wheel-by-wheel preferred) and then using the tire makers load-inflation tables to fine tune.  Excessive tire pressure makes the steering react more easily to external pressures.

Some people like to add steering assist devices but I'm not a big fan of them for DPs with air suspension.  The higher end assists can be set to continuously counteract side forces, making them handy in a continuous crosswind, but not so useful in gusts. Blue Ox Tru-Center is one such.  Devices such as Safe-T-Plus and Steer Safe make some claims to help steer & handling, but in my opinion they are mostly applicable to older chassis with leaf spring suspensions.

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Gary, no alignment was done. They said that the caster was within spec. I do think handling will improve once I fully load coach. Thanks for the feedback.

Just to emphasize what Gary said, tire pressure is critical and over pressure is  a commom problem since many tire workers have been trained to set pressures to the maximum stated on the tire. This is a particular problem with truck service people.  I actually had to argue with the service worker (truck stop Goodyear store) to get the pressure set properly and then he went to the manager for permission (I suspect he fudged even then.)

Ernie

High pressure in the front tires can/will cause various kinds of handling issues, not only in cross-winds.

Gary pretty much touched on everything I was going to suggest.  Weight has a huge impact on the ability of the wind to push a coach around but also any worn components will let the steering move and the coach will go where the tires are pointed.  Chassis design also plays a large role and where the airbags are mounted.  I have noticed that outboard mounted airbags are slightly less affected by the wind but again, this is where weight will play as large or larger role.

Each chassis design has its "quirks" about it as well and things can be done to address them.  For example our Roadmaster chassis' panhard bar position was not what I would call optimal but was positioned due to convenience when the chassis was fabricated.  That being said, I went through a lot of trial and error on our coach to fine tune the handling and upon talking and discussing the issues with others with similar setups I ended up fabricating/machining a Watts Link setup for our coach and now it handles like a dream.  One finger driving in 40+ MPH winds is not uncommon but it took a lot of trial and error, testing and fitting to get the coach to this point.  Many times I have to really look at surrounding trees and/or weeds on the side of the road to determine if the wind is indeed blowing or not the handling is so good.

I also had noticed a few years ago that although my rear thrust angle was "within spec", it was not optimal for the style of roads that I travel on so I cut my rear trailing arms apart and modified them to address the thrust angle and while I was at it I added a bit more thrust angle to compensate for road crown so the coach is now pushed into the center of the two-lane highway's road crown.  The Watts Link that I fabricated was merely the cherry on top as the thrust angle correction made a HUGE improvement.  Although the Watts Link was more work to fabricate and machine it didn't improve the handling as much as my thrust angle correction but sure added that last little bit of "finesse" that I needed to be thrilled with driving my coach.

Mike

Look into improving your POSITIVE CASTER,, a major improvement in overall stability.>>>Dan

Mike, if we still lived in Utah, I would try to hire you to fine tune our coach. We are brand new to Class As, and we have driven it about 900 miles so far. We both commented on how much work it was to keep it on the road, but just thought we weren?t experienced enough. I now know the tire pressure is a lot of our issues! Pretty empty coach driving home, and the tires are at almost max pressure. Duh! We will finish loading it now we are close to home, then get it weighed. I bet it will handle better, but I will still be envious of Mike?s ?one finger driving?.

UTTransplant said:

Mike, if we still lived in Utah, I would try to hire you to fine tune our coach. We are brand new to Class As, and we have driven it about 900 miles so far. We both commented on how much work it was to keep it on the road, but just thought we weren?t experienced enough. I now know the tire pressure is a lot of our issues! Pretty empty coach driving home, and the tires are at almost max pressure. Duh! We will finish loading it now we are close to home, then get it weighed. I bet it will handle better, but I will still be envious of Mike?s ?one finger driving?.

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I'm not gonna lie Kevin, that one finger driving is pretty sweet.

When we first purchased the coach in 2007 I liked the ride but didn't care for the pull to the right and the bit of wandering that it had.  I had it aligned and was told it was "within spec".  Like a dummy at the time I accepted and thought that's just the way it is and is going to be.  In the first several years a 400 mile day would wear my a$$ right out by the time we got to camp because of all of the sawing of the steering wheel and stress of keeping it on the road. 

Finally about 4 years ago I said that's enough, I'm going to get to the bottom of this.  I had heard of a wiggle test, which consisted of sticking a long 2" square tube in the receiver and going to town trying to move the coach around.  I put my son on the end of the 10' tube while I crawled under the coach and began inspecting each and every suspension component.  THAT is when I saw the play that took place in the OEM bushings and really noticed it at the end of the H-frame opposite where the panhard bar was placed.

Upon discussing with a couple of guys I met on another rv forum that were experiencing similar issues it was determined that something had to be done to make improvements.  There were some differences as they each had the RR8R or RR8S chassis whereas I had the S-Series (tag axle) and was the only one of the group with a tag axle coach trying to fine tune his coach.  First thing I did was replace all of my suspension components with ATRO bushings which have a higher durometer rating than the OEM rubber encapsulated bushings.  This helped some but was marginal.  Doing the wiggle test we still detected movement of the entire H-frame at the end opposite the panhard bar.  While discussing with fellow RV'ers devising a plan I opted to perform a more detailed alignment of my own where I could see exactly where the wheels were pointed.  In my opinion this is not as revealing as some think because on a solid front axle there is marginal results you can get due to the few adjustment options.

When I went around to the rear and checked the relationship of the rear axle with the front is when I was shocked.  Basically the rear axle was moving over several inches by the time they got to where the front tires were.  BINGO, there's my pulling issue, or pushing is more correctly stated.  The rear axle had negative thrust angle which was basically pushing the coach, rear steering the coach, to the right.  If I didn't have a firm grip on the steering wheel driving down the interstate the coach would try to go into the ditch within about two lengths of the coach, let go of the wheel and almost took a hard right.  This was exhausting to drive due to constantly having to input force to the steering wheel and it was even worse on two-lane highways with road crown.

As you know there really aren't any adjustments on our RV's like there are on OTR trucks.  I contemplated machining some adjustable sleeves in order to do a trial and error road test but didn't want the hassle of all of that work so I did some calculations to determine exactly how much the front axle needed to be moved forward to bring the rear axle (and ultimately the tag axle as well) into proper alignment with the front axle.  I then added about .032" to apply a bit of "push" to the left so on two-lane highways it will push into the crown of the road.  I cut, lengthened and sleeved the rear trailing arms on both the drive axle and tag axle on the left side of the coach and it handled beautifully after the first road test.  On flat interstate if I completely let go of the steering wheel it will slowly "drift" to the left within several hundred yards but on normal two-lane highway (which we usually travel) I can let go of the steering wheel and it goes straight as an arrow.

With everything handling so well and being ecstatic with our coach at this point I still wanted to see if I could improve it any more.  My wife says I can't leave anything along, but I don't know what she's talking about.   That is when I decided to built a Watts Link and apply it to the end of the front H-frame opposite the panhard bar.  This is where I was still seeing some play doing the "wiggle test".  This presented some obstacles as I discovered that on our coach the genset was positioned more rearward, closer to the front axle, than on any other Monaco coach I had crawled under.  This would require some modification as well before I could even get started on the Watts Link.  We call Monaco's snowflakes for a reason as I have yet to see two identical and each one has their own idiosyncrasies to deal with.  My diagnosis was that on those long constant radius curves there was still enough give or play in the suspension bushings that the weight of the coach was causing the bushings to flex due to the placement of the panhard bar.  This was requiring a bit more steering wheel input on my part to keep the coach going around the apex of the curve holding a particular line.  After building and installing my Watts Link I was pleasantly surprised that on a long constant radius curve once I set the steering wheel angle going into the curve it will hold that line all the way through and not require me sawing the steering wheel to maintain the chosen line through the curve.  I also saw an added benefit that by installing the Watts Link in the manner that I did, it lowered my roll center and in fact acts much like an added sway bar.  I can handle canyon curves much, much better than previously with minimal body roll.

For example if anyone has traveled Weber Canyon on I-84 here in northern Utah when leaving the Ogden area heading east the very first curve has truck speed signs that say to slow to 55 MPH even though the car speed remains at 65 MPH.  I could usually only hit that first curve at around 50-52 MPH if I wanted to stay in my lane and if there was a semi or even a car next to me going into that first curve it was a white knuckle drive, the remaining sections of Weber Canyon usually required me holding around 55-57 MPH until we exited the canyon around Mt. Green.  My wife and I were doing a shake down run just after the completion of my Watts Link but before the long drive to Texas for an rvforum rally several years ago and I hit that first curve at about 57 MPH and it stuck to the road like glue.  My wife was talking and I was concentrating and pushing it a bit, on each curve I pushed my speed up until I was cruising through the entire Weber Canyon @ 65 MPH.  At one point at about 68 MPH one of my dinette chairs fell over and my wife asked why I was smiling and grinning like an idiot.  When I explained the speed at which we just went through there and how well it handles she had no idea we were going through the canyon that fast, that's when she yelled at me to slow down. ;D

In the past 3 years now since I have had my Watts Link on and 4+ years since I really dove into my coach's suspension I can drive 650+ miles a day and not be tired or exhausted from the experience.  Even coming back from the Black Hills last year we made the complete drive (630 miles) in one relaxing day and across I-80 from Rawlins to Rock Springs had consistent 40+ MPH winds and it handled like a dream.  It was moving about slightly, enough to know the wind was blowing but NOTHING like years past and I didn't realize just how bad the wind was blowing until we stopped in Rock Springs to fuel up.

Long story short I would put our coach up against anything on the road as far as handling.  I look forward to canyon driving and grin all the way through.  We've had our coach routinely over/through Logan Canyon (Hwy 89), Teton Pass in WY, Burgess JCT./Pass (highway 14/14A) in WY and Highway 550 between Silverton and Ouray and feel like the coach is much more responsive, safer and actually fun to drive. 

Just in case anyone is interested, I've posted a few videos of the mods to my YouTube channel but I will link them here in case someone may want to see exactly what was done and how it was done.

Here is the first video showing how I corrected the thrust angle on our coach.
https://www.youtube.com/watch?v=FrQR7ERBtOw

Here is Part 1 of the Watts Link build.
https://www.youtube.com/watch?v=Oj-AREsaI-s

Part 2 of the Watts Link.
https://www.youtube.com/watch?v=UGLW7KlqZpg

Part 3 and final video of the Watts Link.
https://www.youtube.com/watch?v=10H5eEB6ADo

Sorry to ramble, I just thought some may find it interesting to hear the thought process and sequence as well as the dedication and ambition it takes to really get the most out of their coach.

Mike

My 2004 American Tradition always exhibited "one finger" control with nothing more than a standard alignment.  But that was also a somewhat more sophisticated chassis than a Bounder gets, and also a heavier coach by some 4000 lbs.  It makes a difference.  That said, I've still driven along windswept highways with the steering wheel angled several degrees to counteract crosswinds.  Hours of that can be tiring, even if it is "one finger" doing the work. Further, seldom is the wind speed and direction steady enough to avoid the need for frequent corrections and that gets stressful over time.

Interesting information, Mike. I get a lot of that (not all) with the Newmar Comfort DriveTM in my Ventana, and I arrive a lot less tired than I did on the same trip in my Beaver. I can even dial it down to one finger (the pinky), if I'm so inclined, but I don't usually make it that sensitive (nor do I usually put it on the heavy end).

For those not familiar with it, Comfort DriveTM  is a self-straightening steering wheel that adjusts to heavy crosswinds so that you no longer notice them, and by closely adapting to your steering inputs while actively eliminating friction, Comfort DriveTM lets you turn the wheel with a light grip that won?t leave you sore or fatigued after a long trip.

However it doesn't pretend to make the kinds of adjustments you made, other than compensating for possible problems.

My new Dynamax on the Frieghtliner Chassis is once again fun to drive. It tracks down the road straight and it is not buffeted by semi trucks passing. When I drove it home from Boise we fought a consistent headwind and as we got closer to I15 on US 93 we were hit by a steady crosswind, which the coach handled very well.

My Fleetwood Bounder 33U was a chore to drive(gas) in that it flexed with every breath of wind and when a semi truck passed it was a quarter turn on the wheel to stay in the lane, the Winnebago Aspect 30J was a bit better, but nothing like the Dynamax.

I have a few friends who have used Safe-T-Plus and swear by the better steering with it. It is only suppose to take about one hour to install and set it correctly. I will be adding it to my class A when I get back to home base.

I installed one on a Ford chassis Class A and was unimpressed. Mostly it just make the steering a bit stiffer. For a leaf spring suspension, a track bar does much more.  More recent Ford F53's have a similar stabilizer device as part of the steering right from the factory. It replaces a steering damper used previously.

For a diesel pusher with air suspension, maybe it depends on what the steering was like to begin with.  If it is one of the low end models with an undersized or poorly balanced chassis, maybe making the steering response stiffer seems like an improvement?

I?m going to add my voice to the tire pressure gang.

When we bought our coach, the previous owner had 110 psi in all the tires. It was NOT easy to drive. It wandered and oversteered badly on curves. The rear end was always wanting to come around on me.

During my first visit to Freightliner Factory Service in Gaffney, I had them do a 4-corner weight. After the weighing I consulted the Michelin tire pressure charts. I found that the rears should only have 95 psi, not 110! I lowered the pressure and went for a drive. I found myself driving and entirely different coach! No more wandering, no more oversteer...it was now absolutely perfect!

Proper tire pressure is absolutely critical to a good handling coach!