How does over inflation affect wandering?

[DAS26miles]

Assuming alignment is correct, how will 5-10 psi over Michellin's recommended psi based on axle weights affect wandering? I'm sure the rear overhang weighted down with cargo and fresh water and B and G tanks doesn't help matters.

[Sfla2]

DAS26miles wrote:
We are taking the Mh out tomorrow for a 2 day trip to the beach 70 miles away. We will see if the lower psi makes handling better. 62 front and 70 psi rear. Otherwise, it's back to the shop.

try 65 frt 75 rear,if to low you roll side to side on sidewall need stiff sidewall

[DAS26miles]

We are taking the Mh out tomorrow for a 2 day trip to the beach 70 miles away. We will see if the lower psi makes handling better. 62 front and 70 psi rear. Otherwise, it's back to the shop.

[rjstractor]

DAS26miles wrote:
My MH weighed in at 4420 front axle, 8540 rear axle and 12960 GVW. I lowered the air to 63 psi front and 70 rear. No food in the MH when weighed, that was the only thing missing. So allowi for 100-150 lbs more on rear axle. Should I drop the rears to 65 or 68?

IMO you are close enough to your max loaded weights that you should have no issues caused by overinflation. You should be running 65 front,80 rear as Ford specifies. The stock size tires give very little margin for overloading, and the typically small motorhome fender well offers poor air circulation for tire cooling. Running underinflated invites tire failure. If you are having handling issues I suspect something other than tire inflation.

[BruceMc]

DAS26miles wrote:
BruceMc wrote

BTW- check see if your new nav radio has the Q22015 update. Some have Q4 2012. You can update them within 30 days of activation. If you have a problem send me a PM

Will do!
We've brought the new unit home, but other than showing it off to family, we've yet to do anything on it.
However, with the pressures set by the factory, it drove very well on the way home. I've no idea what they are set to, but will note the pressures to use as a baseline.
Of course, the Chevy drives much better than the Ford anyway.

[Sfla2]

I think on most older C w/ 14.050 total it should be 65 max frt 80 R, now w newer 1's the total is 14500 now the catch they say frt now 450 more just 50 more on rear. it hard to carry more on frt as where do you put it. forgot mine 65 frt 80 R w/airbags total weight pushing 14 k, handels like a dream no wander 1 hand steering,very very little passing semi sway

[j-d]

80 in our front tires, when I had requested 60, made the coach nearly uncontrollable on the down grade side of a high bridge in a cross wind.

[Oldme]

Over inflation reduces the "tire" patch that touches the road.
You have reduced traction for steering and breaking.
On wet roads it is even worse.

You wear out the center of the tire, as that is what is carrying the load.

[DAS26miles]

My MH weighed in at 4420 front axle, 8540 rear axle and 12960 GVW. I lowered the air to 63 psi front and 70 rear. No food in the MH when weighed, that was the only thing missing. So allowi for 100-150 lbs more on rear axle. Should I drop the rears to 65 or 68?

[Hank85713]

I had some steer wander and was going to have the front aligned to make sure it was right, also was considering adding heavier sway bars. First I added 55-60 psi to the rear airbags, did help, then I went to 65 in front tires and 70 in rears made a world of difference. Try various settings before doing anything Mine is a 12 winnebago aspect scales at around 12500.

[Harvard]

Over inflation REDUCES the effective CASTER TRAIL which INCREASES the tendency to wander.

The caster trail can be increased by adding + caster during the alignment which will reduce the tendency to wander.

[DAS26miles]

BruceMc wrote
I'd suggest trying it & find out what happens. I run 60 to 65 in the fronts and 65 - 70 in the rear, where the inflation charts suggest 55 for my weights.
If it wanders too much, it's easy to pull over and shed some PSI.

I started out running 80 all the way around, but after just a few miles, decided I didn't like riding in an old lumberwagon. 60/65 seems to be the sweet spot for the Four Winds. I didn't have any wandering problems, as the ford is always light in the frontend and had to be herded between the fencerows.

We are picking up our new Sunseeker in a little over an hour from now... so I'll have a whole new machine to learn & tinker on!


Thanks, that's the psi my chart says to use. There was 70 psi in the front and should be 60-65 or closer to 63. Will try!
And congratulations on your new Sunseeker! I have the big Brother Forester 2701DS. Yes, new learning curve and moving everything over. Took 12+ years to get our Winnebago the way we wanted it and trying to get the Forester like that in a few weeks doesn't work.

BTW- check see if your new nav radio has the Q22015 update. Some have Q4 2012. You can update them within 30 days of activation. If you have a problem send me a PM

[DougE]

High pressure in the rear tires should make the sidewalls stiffer and better able to withstand input from the trailer. Probably one of the more dangerous conditions is a low rear tire that allows the rear of the tow vehicle to shift from side to side. As far as rear trailer loading, that figures into a nasty dynamics issue know as polar moment of inertia. The further a given load is from the axle location the more impact it has on the stability of the trailer.

[tpi]

I think the front overinflation contributes to the wandering. I doubt the rear contributes much if any to it. Rear overinflation is detrimental to ride quality-as the isolation of the springs, bushings and body mounts tends not to be the best. IMO if you don't mind the ride pump up the rear up to the sidewall limit.

Harvard may have input here, but it is possible the longer contact patch of the front tires due to lower pressure may increase the effect of caster and have better return to center. If you've ever driven a non power steering car you'll notice lower tire pressure increases steering effort, increases return to center, and is less sensitive (twitchy?) on center.

The longer I've had my motorhome the closer I come to the exact inflation table pressures-with little or no cushion. I like the improved rear ride and the better steering feel. If I'm trying to generate a safety cushion it is by keeping the speeds below 65 MPH and not seeking out the hottest of the hot pavement. Running pressure table spec is running to spec. There's no reason to carry 75 to 80 PSI in the tires when the front tires are specified to carry 50 with the load.

[cgmartine]

The higher the pressure, the smaller the tire foot print on the road, which equates to wandering, rougher ride. On a Class C, try 72 up front and 80 in rear.