Air pressures

[charliem]

[font size="3"]They are for different tires. The tongue label is for the OEM factory specified tires, usually an STxxxx trailer tire. Your actual tires may be different, such as Goodrich AT tires supplied with the off road package. These are wider and can support the required load at lower pressure. Either will work. Don't exceed the sidewall pressure of 50 psi.
[/font]

[stevesanders]

The maximum pressure stated on the sidewall of a tire is only half of the sentence that's really abou the maximum LOAD that the tire can safely support.  It will say something like Max Load 1750 at 80 PSI Max.  The air pressure is what's carrying the load, but the tire structure is what's containing the pressure.

The problem with these trailers that raises so many questions about tire pressure is that they are so much lighter than most trailers.  The typical trailer weighs almost as much as the tires are capable of carrying, so the maximmum pressure is correct.  However, a Quicksilver typically has a loaded weight that's about half of the maximum load rating of the tires.  If you have two tires that can carry a total of 3,500 pounds on a trailer that weighs maybe 1,200 pounds, you don't need maximum pressure because you're nowhere close to maximum load.

So why does the sticker on the trailer tongue say 65 PSI?  The answer is lawyers and legal liability.  It is safer to overinflate than to underinflate, so recommending overinflation reduces litigation risk.  (Think about the Ford Explorer roll-over lawsuits of hte 90's.)  However, as mentioned in another thread in this forum, inflating tires to the MAX pressure will cause these campers to bounce.

I have always maintained 35 PSI in the tires on my QS 6.0.  It rides smooth and the tires wear evenly.

These comments are largely based on training received when I worked in the passenger and trailer tire industry.

[stevesanders]

Excellent! Thanks for the charts!!

Many people simply reject the entire concept and insist that max pressure is the only safe option.

[charliem]

[quote timestamp="1471529017" author="@stevesanders" source="/post/23946/thread"]Excellent! Thanks for the charts!!

Many people simply reject the entire concept and insist that max pressure is the only safe option. [/quote][font size="3"]Given manufacturers' attempt to cut cost with minimally rated axles and tires, max sidewall pressure is the safest assuming the tires will carry the load at that pressure. You don't see many overrated E range tires on stock campers. [/font]

[david]

[quote source="/post/23957/thread" timestamp="1471562534" author="@charliem"][quote timestamp="1471529017" source="/post/23946/thread" author="@stevesanders"]Excellent! Thanks for the charts!!

Many people simply reject the entire concept and insist that max pressure is the only safe option. [/quote][font size="3"]Given manufacturers' attempt to cut cost with minimally rated axles and tires, max sidewall pressure is the safest assuming the tires will carry the load at that pressure. You don't see many overrated E range tires on stock campers. [/font]
[/quote][p]I agree. In the relatively rare case where you installed bigger, higher load rated tires you could get by and improve tire life by reducing tire pressures if towing a much lighter trailer than the tires can support, but you better know exactly what you are doing.[/p][p]
[/p][p]David[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]
[/p][p]n the relatively rare case where you installed bigger tires with a higher load rating, you could reduce tire pressures from the sidewall figure. But you better know what you are doing.[/p][p]
[/p][p]David
[/p]

[stevesanders]

Since this discussion thread is in the Quicksilver pop-up camper forum, tire and axle capacity vastly exceeding the load of these particular trailers is not the exception, it is the rule.  The heaviest Quicksilver, the 10.0, weighs in around 1,200 pounds (empty) and is riding on tires that can handle about twice that load.  If we were talking about Camplite or any other line, I would agree that the in-service weight of the trailer is about equal to the max load on the tires and axles, but we are talking about truely light-weight campers here.  I agree that overinflation is safer than underinflation, so if in doubt, go high.

My 6.0 (650 pound empty weight) is riding on tires that can handle 1,050 pounds EACH (at 80 PSI).  The sticker on the tongue says to inflate them to 80 PSI.  If I do that, it bounces like a basketball going down the road!

The first thing you really have to understand is if you have bias ply or radial tires.  If the tire size specification includes the letter "R", then you have radials, if it does not you have bias ply.


If you have bias ply tires, the sidewall profile should look the same all the way around the tire.  If there is any bulge at all at the bottom of the tire, it needs more air.  As long as the bulge is gone, you have at least the minimum to carry the load, but you don't want to operate at minimum.  If you add pressure until the outer edges of the tread start to lift off the ground because the tread is rounding out, then you have too much pressure.  (Overpressure tread edge lifting is much harder to see than underinflation bulge.)  

If you have radial tires, optimal flat contact patch is obtained with a small amount of sidewall bulge where the tire contacts the road, but wear to the edge of the defined tread is still the goal.

On either radial or bias ply tires, look at the wear pattern on the tread after driving a while.  You will be able to see what part of the tread is contacting the ground.  You want the visible contact area to come right to the edge of the tread, but not beyond.  The contact patch of the tread should be flat against the ground, not concave (underinflated) or convex (overinflated).  If you add pressure until the wear pattern no longer reaches the edge of the tread and then lower the pressure until it does, you will be at the correct pressure for the weight of your trailer.  It's likely that one side will be heavier than the other and therefore require more pressure.