More LTX M/S tire pressure?

[TomW]

I normally tow with a gas-guzzling, vintage Suburban with big ole E load range tires. I'm comfortable towing with 44 psi front, and 65 psi rear.

Economics has forced me to use my wife's '09 Yukon for the next trip due to the amount of miles we have to cover.

The door sticker wants 32 psi tire pressure all around, and makes no distinction about tire pressures for towing.

Today's test ride had little bit of a "tail wagging the dog" feel about it.

The Michelin LTX M/S tires I just had mounted have a max pressure rating of 44 psi. I'm thinking about boosting the all-around pressure to either 38 or 40 psi for a better tow. Any thoughts?

Thanks,
Tom

[Gene]

Sounds like those are Load Range C tires. The sticker on the door gives pressures for an unloaded vehicle—a couple of passengers and a few other items. I'd put 44 psi in them for towing, but you can check tire charts for the pressure recommended for the weight of the truck axles and specific tires. Some tire store chains have charts online or Tire Rack does too.

Gene

[Bill M.]

I do not think there is any real advantage to running them less than the full 44 lbs max. for towing.

[SteveH]

Run the rear tires especially at 44. The front you can run at 35. That will reduce the tendancy to sway, but if you run all four of them at 44, it probably will not.

[TomW]

Originally Posted by SteveH

... That will reduce the tendancy to sway, but ...

Thanks, SteveH, for the response. Sway, in the sense of being bothered by wind or passing trucks, was not the issue on the test ride. My observation was squirrelness in general.

I kinda lean towards pumping all the tires up to the same pressure since much time (and a few dollars) were spent dialing in the Airstream's Reese Dual-Cam to distribute the tongue weight to all four wheels.

Tom

[SteveH]

I know what you are saying, Tom, but try it both ways. With the front aired up the same as the rear, the stearing response will seem too fast, and actually add to the squirrlyness you experienced, it has been my experience.

[Ahab]

Tom W, I run mine at 40psi

[wingfoot321]

Michelin did not put 44psi on the sidewall without considerable thought.

And, that is 44psi cold.

Load range C is not a lot of tire when you are in trouble.

[slowmover]

Load and pressure must match. And stay "within" vehicle manufacturer guidelines for FF/RR bias (see owners manual).

The tire dealer can check the data he has to help dial in the pressure.

Again, a scale ticket from a weight scale is your friend: With and without trailer to find the individual axle average.

Too much pressure reduces the tire contact patch and this is NOT the right way to achieve best handling & braking. Too little heats the tire unnecessarily and shortens life.

I have a set of pressure values to use for my truck:

1] solo/empty,

2] solo/loaded; and

3] solo/loaded + towing.

According to tire engineer Barry Smith the ideal pressure on the TV is the one where

after an hour of steady state driving, the pressure rises no more than 3-5 psi from the cold measured value.

(Raise or lower in 5-psi increments and test again until ideal number is achieved).

Example: where DODGE tells me that 50-psi is correct, a morning drive will reveal if the pressure rise is spot on. If not, then I can move to 55-psi and repeat test. But I cannot go below 50-psi even though MICHELIN shows this as acceptable per weight scale reading . . it violates the DODGE number (which is acquired through extensive testing on their part).

In a sense, I want the lowest number, but no lower. Higher offers no benefit.

As a second insight, the truck industry spends an enormous amount of money on tires. Pressure according to load is the mantra. Each trucking company works with one or more tire service representative to come up with the ideal value for their trucks. One company down the street from another doing the same work can arrive at different numbers even where the tractor & trailer are nearly identical (as are loads). One may call for 105-psi and the other 95-psi.

There is a great deal of time and money involved in setting those values. For RV'ers we are, IMO, well advised to follow the example of so high, but no higher for longest life and best performance.

The best TPMS is also a good idea.

.

[SteveH]

The required tire pressure while towing is as much about stability as it is about load carrying capacity.

First, your vehicle must be able to carry the additional weight the trailer puts on it, and second, it's extreemly important your vehicle has the stability to manage the trailer.

The tire pressure that will carry the weight (from the tire spec charts), may not be enough pressure to make the tire stable enough to manage the trailer. That pressure must be found thru experimenting while towing the trailer, it has been my experience.

[TomW]

Thanks, everyone, for the responses.

Getting the Yukon ready for the trip took more effort than I thought it would. The biggest surprise was the new shank (black part in picture) that had to be purchased to accommodate an unusually high receiver.



Fortunately, it only took two iterations of setting up hitch height/pitch to get the same amount of drop at the Yukon's fenders with the Overlander riding level. I used 550-lb bars with the Airstream's Reese Dual-Cam. The bars were more than sufficient: Sway was NOT an issue.

I went with Ahab's post of 40 psi all around, and never felt any reason to change it. The truck's on-board tire pressure monitor let me see that the front tires heated to 44 psi, and the rear to around 46 over the course of the 2000 mile vacation.

While 10.4 mpg was a little lower than hoped for, it sure beat the Burb's 5-8 mpg on mid-grade gas for such a long trip.

Looks like we will be using the Yukon more for towing.

Tom

[ROBERT CROSS]

Tom,

Sounds like you've got the TP thing squared away. When it's time I would consider a load D LT replacement.

Noticed in your pic....I would run your umbilical over the top of the A-frame thru a D-lock pin.

Bob

[TomW]

Bob,

Airstream originally provided a nice, grommeted hole in the top of the Marvel coupler for the umbilical.

I didn't forget to do it the right way, I just didn't remember...

Tom

[ROBERT CROSS]

Originally Posted by TomW

Bob,

Airstream originally provided a nice, grommeted hole in the top of the Marvel coupler for the umbilical.

I didn't forget to do it the right way, I just didn't remember...

Tom

I hate when that happens....I spend time with my morning coffee deciding what I need to forget that day to make room for what I may need to remember.

Bob

[idroba]

Originally Posted by TomW

Getting the Yukon ready for the trip took more effort than I thought it would. The biggest surprise was the new shank (black part in picture) that had to be purchased to accommodate an unusually high receiver.


Tom

For anyone else who is dealing with the high hitch box issue on newer tow rigs (my Jeep Grand Cherokee has the same issue) there are two Reese shanks which will allow the hitch and ball to be lowered. The one shown in the photo is a Reese 63971 but they also make a 3215 which will lower the ball about the same amount but has a shorter shaft and will put the ball 1.5 inches closer to the bumper. I am told even that small difference will change towing dynamics some, closer being better.

I found no one in my best parts place knew or understood the differences from one shank to another. I had to go to the Reese web site to find all the ones they made, with the dimensions and differences between them.

[TomW]

Originally Posted by idroba

...I found no one in my best parts place knew or understood the differences from one shank to another. I had to go to the Reese web site to find all the ones they made, with the dimensions and differences between them.

You & me both, idroba!

Tom

[TomW]

Originally Posted by idroba

.. they also make a 3215 which will lower the ball about the same amount but has a shorter shaft and will put the ball 1.5 inches closer to the bumper. I am told even that small difference will change towing dynamics some, closer being better...

The cool thing about the 63971 shank is that its extra length allowed us to fully open the Yukon's liftgate while hitched.

Tom

[slowmover]

Originally Posted by SteveH

The required tire pressure while towing is as much about stability as it is about load carrying capacity.

First, your vehicle must be able to carry the additional weight the trailer puts on it, and second, it's extreemly important your vehicle has the stability to manage the trailer.

The tire pressure that will carry the weight (from the tire spec charts), may not be enough pressure to make the tire stable enough to manage the trailer. That pressure must be found thru experimenting while towing the trailer, it has been my experience.

Which is why one weighs the rig to find that axle weight average [wheel position], again.

Stability is a question larger than just tires (mainly, tire type) as it includes "better" shock absorbers, anti-roll bars & bushings (for starters). Then there is slack [slop] in the steering gear, worn body bushings, etc.

It's worth looking at the percentage change in any experimentation, not just numbers.

But load & pressure tables still rule within the vehicle manufacturer specified range. Low enough to meet the table value, high enough not to heat up past 5-psi beyond the cold value. This meets the test for best transient response and braking. Higher is not better.

.

[SteveH]

Originally Posted by REDNAX

Stability is a question larger than just tires (mainly, tire type) as it includes "better" shock absorbers, anti-roll bars & bushings (for starters). Then there is slack [slop] in the steering gear, worn body bushings, etc.

It's worth looking at the percentage change in any experimentation, not just numbers.

But load & pressure tables still rule within the vehicle manufacturer specified range. Low enough to meet the table value, high enough not to heat up past 5-psi beyond the cold value. This meets the test for best transient response and braking. Higher is not better.

.

Rednax, the thread is about tires, and more specifically tire pressure. If you don't understand that a higher inflation pressure in the tow vehicles tires provides for a more stable vehicle, especially the rear tires, I don't want to discuss this with you any more.

Have a good day.

[slowmover]

Stability is not static. A vehicle with a heavier load requires a higher pressure, granted, but higher-than-necessary inflation pressure does not add to vehicle stability . . it may in fact reduce the ability of the vehicle to maintain adequate contact with the road surface. Tire type, tire pressure, vehicle suspension all must work together. When one is out-of-whack with the others is when TV performance declines.

On my diesel-engined pickup, for example, the FF tire pressure does not change for any increase in weight from empty upwards. But if I leave the RR tires at too high a pressure for unhitched or unloaded or both, the rear can quickly lose traction. Some sidewall flex is expected and beneficial (depending on a given vehicle). Same for tread flex.

The word stability is possibly a stand-in for "road feel" . . that higher pressures than necessary seem to add to rig performance. A TV with poor steering feel (4WD straight-axle pickup is classic in this instance) will seem more stable with higher than necessary pressures . . until it matters.

We'd have to go into understeer and oversteer to possibly clarify this, but let's keep in mind that hitch rigging guidelines are, currently, about maintaining the same steering and braking response as when not hitched together to another vehicle. That is a given.

The pressure range specified by the vehicle manufacturer must be respected. Another given. The range of pressure values available in their recommendations has to do with loads carried by that vehicle. Their extensive testing -- especially since the Ford Explorer/Firestone fiasco of a few years ago -- ought to be respected. None of the rest of us, not even the tire manufacturers, can state "what works best" for a given vehicle under different loadings.

A tire dealer can reference the pressure values for a set of tires to confirm close match of pressure and load for those who wish to come closest within the vehicle manufacturer guidelines.

Start with numbers -- a baseline -- using weight scale values and the vehicle info. Same as with setting up hitch rigging (and done concurrently). Test with pressure rise and monitor temps as well as can be done.

Diagnosis of better and worse is dependent upon agreed values for given states of mechanical relationships.

Setting tire pressure is -- like hitch rigging -- a formula. If A, then B . . weight per wheel position mandates a minimum pressure. Then, past a certain given point are other relationships to be addressed as contributing or compounding effects.

The interaction of components -- of systems -- can be diagnosed when given numbers are adhered to in a baseline (as is done so well in this thread.)

Experimentation with pressure past that is on the owner . . but it cannot be a recommendation to others as general advice when, in fact, it may be that new shock absorbers and the replacement of some worn bushings is all that the TV "needs" for "stability". Or a hitch rigging adjustment. Etc.

We can play around with definitions of stability but in the end it will come down to tires maintaining traction in a familiar way.

And that is best found when the baseline is composed of numbers that can be verified against guidelines.

.