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Old 06-02-2012, 11:54 AM   #15
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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.
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Old 06-02-2012, 12:01 PM   #16
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...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!

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Old 06-02-2012, 12:05 PM   #17
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.. 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.

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Old 06-02-2012, 06:05 PM   #18
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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.

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Old 06-02-2012, 08:47 PM   #19
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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.
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Old 06-05-2012, 05:37 PM   #20
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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.

.
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Old 06-06-2012, 07:44 AM   #21
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Stability is not static. A vehicle with a heavier load requires a higher pressure
.
With that statement, I agree.
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Old 06-07-2012, 05:11 PM   #22
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Well, we've had us a fine ol' " . . irked ya, huh?" session to keep the dawn patrol at Dairy Queen satisfied over several mornings. I see from other posts that -- no surprise -- that we are likely to preach from the same book, but are arguing endnotes on this chapter.

See you in the funny pages.

.
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Old 06-07-2012, 05:58 PM   #23
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To wrap this thread up, I was comfortable with running the Yukon's tires at 40 psi for the trip.

My blog will be updated in a bit about more trip details. You can tune in now if you care about the Overlander's new awning mounted just in time for the 2100 mile trip (link in my signature).

Tom
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