Wandering at highway speeds

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Alpena Jeff

Alpena Jeff

Well-known member
Joined
Dec 7, 2014
Posts
965
Location
Up North - Michigan
35 ft diesel pusher
GVWR 35,000
GAWR front 12,000 - rear 23,000
CAT scale weights packed and ready to roll: front 10,940 - rear 18,780 - toad 4700 - gross weight 34,420
Placecard behind drivers seat shows front 130 - rear 120
Tires - Michelin 275/70R22.5 J XZA2 Energy
Tire pressure front 100 - rear 95
I feel my tire pressures are good based on the spec sheet from Michelin. Please correct me if I'm wrong.

Wheelbase/length ratio just under 50%

Here are my questions: (this is my first ever coach)
As of now my comfort speed on the highway is 62-63. On good roads in good conditions all is well. Any faster the coach gets a little squirrely. Being passed by trucks we get squirrely.
Is what I'm experiencing normal? Do you all drive faster than I do?
Does my shorter wheelbase play into this?

We really love this coach, my 30 mile or so test drive was on a highway and conditions were good. It handled great.
I just don't know yet what is normal and what is not.

Is there more info I can provide?
As always, thanks.



 
Jeff-

Based on the Michelin weight tables I saw online, your pressure may be a little high on the rear.  It shows 85 lbs as the correct inflation for that weight.  Not sure how much of a difference that would make.  Ignore the placard, as that just shows the max inflation.  You did the right thing by weighing.  My coach was squirrelly when I first got it, but that's because it was 12 years old and the shocks and anti-sway bar bushings were shot.  That shouldn't be the case on yours.  I replaced with Bilsteins and polyurethane bushings and had a world of difference.  Again, you shouldn't have that problem.

I imagine one of the steering stabilizer devices would counteract the squirreliness to some extent, but I don't have any experience with that.

As far as speed, I generally cruise around 65-68 with no problems.  I don't like to go faster than that, mostly because of the hit in fuel economy.
 
Thanks for the reply Scott.
Yea, I wasn't sure what to do with the rear axle as I'm 650 lbs below their lowest mark. I do know underinflation is bad so I intentionally missed high. Maybe too high.
I will make the correction and see what happens.
Maybe others will stop by with more suggestions.
 
POPULAR MECHANICS MAY 1973:
START QUOTE:
If too little caster exists, the car will wander and weave,
thus necessitating constant corrections in steering.
END QUOTE:

There are at least two ways to increase the effective
runtime caster (see Self Aligning Torque):
1. Decrease the tire inflation pressure to the required
minimum for load (to increase Pneumatic Trail), and or

2. Increase the caster angle during an alignment
(to increase caster trail).

If you find an improvement in reducing the tire pressure
you will be amazed what it is to add +2 degrees of caster.
 
being a newbie you may be looking to close to the road, try looking a little father down the road and relax your grip on the wheel.
before you know it all this will be old hat and you will have to find new thing to worry about.
 
Does it feel like your chasing it with the steering wheel back and forth maybe 2-3". My 36 ' Safari does this on rutted roads most noticeable.I increased my caster 2 degrees and it helped a lot but not all.I am going to instal tiger trak bars before my next trip in May,as I think it is tail wag.
Your 2016 Ventanna shouldn't have this problem to the extent of my 22 yr old Safari.
 
I drive 58-60 most of the time.

There are a lot of variables like wind, temps, road surfaces, weight of unit, air pressures etc.

Many roads have a crown to shed water and that can enter into the effects you see too.

When trucks pass me (and most do) I know that when they get about to the middle of my coach I need to
countersteer in their direction some as if I don't they will push me to the right.  After they go by me I can relax the
countersteering and that keeps me going fairly straight.  Cars have little if any effect.

So I believe that it is a learned habit that you will get use to, the more you drive it.

It sure make driving a car or riding a motorcycle easy by comparison.  But most of us have been using cars most of our life.
Your MH is way different since it weighs about 6 times what your toad does, right?  And is twice as tall?
 
I will drop the rear pressure to 85 and see what that does. If I notice any improvement or if not I will look into an alignment. Just read up on caster alignment so we will see.
I generally focus prolly 100 yards down the road, arms on arm rests and steer with thumb and forefinger with light grip. This is my norm until we start to sway then all bets are off! It's likely a trust issue I have when that semi is 2 feet away and pushing me out then sucking me in. My sphincter tightens and therefore grip does too.
I believe the ride should be more comfortable, more stable, less stressful than it is. I will do what I have to to fix it!
Any other ideas?
Thx, Jeff
 
Jeff,

All the rigs I've had with squirrely steering had the cold pressure in the front tires too high. Using the manufacturer's tables (after weighing, of course) cured my problems.
 
Larry, Michelin chart shows front 100psi for 11,250 lbs. My front weight is 10,940.
I should be good on the fronts. I'm definitely over on the rears which will be adjusted before I hit the road again.
Got anything else? Our coaches are very similar except you're longer.
Thanks.
 
My 38 footer comes in at 34750 with 22.5s I have perfect handling at 92 front and 85 across the rear, I have a "sweet" spot at 64 MPH and constantly average 10 MPG>>>>Dan
 
Jeff,

Have you played with your adjustable steering for different speed/road conditions and and passing trucks to see if tighting up  the steering wheel (increasing no.) will effect of that squirrely feeling?
 
I have ferfer. I run it very low in the city and have tried various settings on the hiway. The higher settings help some but it also has a memory that fights you once the side wind stops. I like the comfort drive I think...it's still new to me..
Thanks for responding.
 
The extra 10 psi on the rears won't effect the handling enough to be of interest.  85 psi is the MINIMUM for the load, not the "recommended" pressure. You should probably be 5 psi above minimum just to compensate for daily temperature changes and the occasional extra load, so +10 is not excessive.

I'm inclined to agree with beaverfever - you may need to get more comfortable with the handling to prevent newbie "over-steer", sometimes called "fidget steering".  Get your vision focused further down the highway, relax, and stop the minute corrections.

The rest is probably the relatively short wheelbase/length ratio. It makes the rig more susceptible to passing trucks and crosswinds, as well as the almost invisible ruts in most heavily traveled highways.
 
Gary, just so I understand.
My running weight rear axle is 650 lbs below Michelins lowest chart entry of 85psi.
Are you saying 85psi plus 5psi is the lowest inflation I should have on the drive tires even with my low weight?
And dropping psi from 95psi where they are now to 90 or even 85 won't make a difference in handling?
I totally respect your opinion. I just think this coach should hold the road better.
I do focus on relax, light touch and focus down the road best I can. Maybe I just need more time.
 
Rear pressures won't really affect handling, but front pressures can make quite a difference, especially if they're over-inflated. Our (new) coach wouldn't drive in a straight line until we weighed it and adjusted air pressures accordingly. In our case, we were grossly over-inflated (by the dealer), and lowering the pressures to the tire manufacturer's inflation chart made a huge difference.
 
Consistent with what others are saying, I implied in my post that the rear pressure wouldn?t have much effect on the handling.  I probably should have stated that more clearly.  The fronts would have a much greater effect, but sounds like those are good. 
 
Is there a chance my weights are incorrect! It was also my first time on the scales. Maybe I wasn't positioned properly?
Don't know if that's even possible. I'm reaching now!
 
I agree with Gary. If reducing tire pressure is going to make a difference in how it handles, the front tires will be impacted more than the rears. I have a 38' so we're close in size and after weighing my coach, I dropped the fronts from 105 to 90 and the rears from 95 to 85. The problems I had when trucks pass me virtually disappeared. But, comma, at the same time, I had also become more familiar and comfortable with how the coach drove overall and was able to drive more relaxed, keeping my vision a quarter mile down the road most of the time, only occasionally watching the lines passing by. So your issue may be corrected by either thing. Unless I have a strong cross wind blowing me sideways, I don't have a problem keeping the thing in a straight line.
 
Tom.
I composed a reply but it got whacked somehow.
Short version, thanks for responding. My front psi is good according to my weight and tire chart.
I could drop the 5 psi that I added based on what I read here but no more.
For now I will work on technique and patience.
Best, Jeff
 
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