I am having difficulty deciding which tires I want/need.

The nameplate lists Load rating G at 100 lbs in front, 105 lbs in rear. This works to match GVWR, front and rear GAWR. I am looking at Hankook AH12 series Load G (14 ply) which has max air pressure of 105 lbs.

Also looking at Hankook AH12 series Load H (16 ply) because it allows higher air pressure, up to 120 lbs at a slightly higher price, but will be a special order. By the time I decide, the "G" might be hard to get, as I found only 7 in Tucson.

My reasoning for choosing the H rating is because it allows me to boost air pressure to perhaps 110 lbs to have a little extra margin for air loss before slipping below the suggested 105 lbs. The G tire does not afford this luxury of a higher upper pressure margin.

Now this may seem silly to some, even me sometimes, that silly legal extra 5 or 10 lbs. But that is why I am posting. I need a sanity check. Opinions appreciated.

P.S. I will be buying 6 new tires in a day or two.

quote:

Originally posted by garryp:


Now this may seem silly to some, even me sometimes, that silly legal extra 5 or 10 lbs. But that is why I am posting. I need a sanity check. Opinions appreciated.

Heavier tires buy you a little more safety.

Since tire pressure will decrease with lower temps, when I head north, I carry 5 psi extra all around as a margin.

How much weight are you carrying on your axles. Before you do anything get you coach weight by axle. The air pressure on the sidewalls is MAX for the tire, but you need to know how much weight the tire is carrying.

I decided to buy the AH12 G rating. Here is my logic.

As Rusty said, I wanted to be able to go up in pressure to add margin and stay within tire rated max pressure. If I am running with a GVW equal to GVWR that would indeed be about 100 and 105

I relooked at the figures that I had jotted down, as I did weigh front and rear axles a couple days ago for this purpose.

Yes, the recommended G tires, when loaded with GVW = GVWR of the vehicle, would have to run at max pressure, with no upside margin for tweaking.

But I decided that the key to the question is, when wet, I am running at about 2700 lbs below GAWR on the front (1350 per tire) and 2500 below GAWR on the rear (625 per tire).

Then I pulled out the Goodyear pressure vs. load for a 11R22.5 as a proxy for the gov standards that the load rating is predicated on.

On the front, 1350 below max rating per tire would suggest that front psi should be around 80 lbs for the actual wet load.

On the rear, 625 lbs below max psi per tire would correspond to a pressure of 90 psi for the actual wet load.

In reality, if I base running psi on actual load instead of GVWR/GAWR load then I will be running at a correct psi for my actual weight. And that would be about 90 psi for the rear and about 80 psi for the front. Voila! In reality I do have a margin for adjustment in both directions when psi is based on actual weight instead of max rating.

Note: Front GAWR is 12,000, Rear GAWR is 23,000. The psi shown on the coach label of 100/105 are for this max G rating. I am actually running about 9,300 front and 20,400 rear wet, excluding a couple hundred for clothing, food, and gadgets. The liquids are the largest variable loads that I have. (150 gal diesel, 125 gal water tanks, large propane tank)

As Gary suggested,after I am mostly loaded, I will take another weight measurement and adjust tire pressure accordingly with fewer approximations.

This is the thought process that the fanatical (no disrespect intended) four-corner weight process accomplishes with more precision. But with tire gauges possessing perhaps an accuracy of 5 lbs measuring tires that are half on the sunny side and half in the shade with a varying slow seep of perhaps 0 to 5 lb a month, I think axle analysis is adequate.

The real pain I will suffer is discarding 6 tires that look perfectly good because they are about 9+ years old. I have had 2 flats, one was a blowout that caused about $2000+ of collateral damage.

And as a bow to Bill, I am buying Hankook AH12 tires which I think are relatively heavy duty.

Am I still crazy? Thanks for the comments, pro or con.

QED

Since i put on a tire pressure system i have found that within about 10 miles or starting out each day that my tire pressure increases about 10-15 percent. I use to run 100-105 cold on the front but now run them at 90 cold and end up about 103-105 after they heat up.