Tire Pressure and Torque

[gmw photos]

Originally Posted by nickmeloy

In the temperature and pressure ranges that we are dealing with in this discussion, dry air and dry nitrogen will both behave pretty much as the Ideal Gas Law predicts. With the measuring equipment that we use to monitor our tires (TPMS and tire pressure gauge), it is unlikely that we would be able to measure any practical difference.

....aw come on Nick....you're cutting into that nice fat profit/gimmick that the tire stores are selling.....nitrogen and those really cool green valve caps....

[Cardinal283]

Originally Posted by nickmeloy

In the temperature and pressure ranges that we are dealing with in this discussion, dry air and dry nitrogen will both behave pretty much as the Ideal Gas Law predicts. With the measuring equipment that we use to monitor our tires (TPMS and tire pressure gauge), it is unlikely that we would be able to measure any practical difference.

Nick... My apologies. I was having a brain fart over here. Ideal gases expand at the same rate regardless of what type they are. Sorry it's been a while since I've had to do any physics. Nitrogen in the tires has to do with it not permeating the rubber. Not with expansion rates. Thank you for the correction. : )

[Jim A]

It's been my understanding through the years, several different trailers and tires and numerous discussions with tire "experts" that the "max" tire pressure on the tires is the pressure the tires need to be inflated to to carry the maximum load indicate on the tire. It's not the maximum safe pressure in the usual sense. Anyone that has followed tire pressures with the tire monitoring systems know that the actual running pressures range from 5 to 8 lbs on the road above the cold start temperatures at a constant air temperature. Depending on sunlight, rain, and other such odd features of travel. Heaven forbid that you see what the tire pressure is mid afternoon when you start out at a cold inflation at 30 or 40 degrees and have a max temp during your days drive of 80 deg or above. Even worse is if you start out a trip with a cold inflation pressure of X and a temperature of 20 deg and end up at mid trip with temperatures in the morning of 60 and rising to 90 during the day. You can spend every day bleeding off or adding pressure. I don't see many people doing that. So my comment would be pick a reasonable number such that when the temperature drops, you don't end way under a load capacity for the tires at the early morning temperature. For my new 16 in Michelin's, as well as my old 15 Load range E Maxxis, I've chosen 75. Rolling, that gets a driving pressure of around 82, give or take. As to nut torque, 100 to 110 seems about right based on numerous recommendations. Discount Tires recommendation was 100 lb but I think I'll go with 110 based on the aluminum rim discussion.

[BlackAces]

Originally Posted by Ramblinboy

I just had Michelin XPS Rib LT225/75R16 tires installed on our 31' 2005 Classic along with 16" wheels. The tire dealer recommended 85 psi for tire pressure and a torque setting of 120. Does that seem right to other Michelin tire owners?

If you want to follow industry standards for your new tires you should read the information on your trailer’s tire placard. That information will give a recommended tire pressure for the OE tires. That pressure corresponds to the load capacity each tire needs - according to the vehicle manufacturer - to carry the loaded trailer. Now look at a load inflation chart for the new tires and use the pressure needed to match the load capacity of the OE tires. That is your new cold recommended tire pressure.

BA

[mefly2]

Originally Posted by nickmeloy

In the temperature and pressure ranges that we are dealing with in this discussion, dry air and dry nitrogen will both behave pretty much as the Ideal Gas Law predicts. With the measuring equipment that we use to monitor our tires (TPMS and tire pressure gauge), it is unlikely that we would be able to measure any practical difference.

How much of our "air" is actually Nitrogen ... 7/8 IIRC.

[NWGreyhound]

I've been running 70 psi and 110 ft lbs on my new Michelin 16" LTX MS/2 and Sendel wheels. I now have about 2000 mi and so far it seems right, tows right, hasn't gotten warm at all and the lug nuts are staying tight.
I'm a happy camper now.

[ZoominC6]

We've been towing for many years, 20+, and have found that trailer tires work best at 65lbs and 65mph. Just my 2 cents worth.

[m.hony]

I run 65 psi in my Good Year Marathons.
In my mind when I get 16" wheels and tires I will still run 65 psi.

[mstephens]

Looking at the spec for that tire here: http://www.tirerack.com/tires/tires....tnum=275R6XPSR

I see 80 PSI as the max. I'd look very carefully at the Michelin spec for your tire and go by that.

My Airstream Manual has the torque spec as 120# for lug nuts. I carry a torque wrench just for this purpose.

[jcanavera]

When I bought my Sendel T03's from Tredit, I asked them for the torque guidelines for those wheels. They told me 120 ft lbs. My manual from Airstream advised 80 ft. lbs for the original Alcoa's. I had some concern about torquing those lugs almost 50% higher than original specs, not knowing if the hub spindles could be torqued that high. I decided to torque to 100 ft lbs. I've found that that holds the wheel tight and doing further checking over the past two years, I've found that the lugs pretty much stay at 100.

I run my tires at 80 psi due to the heavy weight of my Classic SO.

Jack

[CapriRacer]

I find it kind of funny that the OP didn't post much in the way of information, but lots of folks have an opinion.

First, what tire size came off? What does the placard say about tire size and inflation pressure? (Please note: It is important to include the letters in front of and behind the tire size. Those letters clue tire folks into what kind of tire is being specified.)

Second, trailer manufacturers are notorious for undersizing the tires on their vehicles. I don't have enough information about Airstreams to know if they do or don't or if they changed (and when), so I would look at placard pressure with a grain of salt - it might be a little on the skinny side.

I think an upgraded tire combo also needs to upgrade to the load carrying capacity. If you'll notice the load tables are minimums, not recommendations. I recommend you use a minimum of 15% over capacity.

I also recommend you weigh the trailer - in the worst possible case you can imagine. Weight individual wheel positions if you can. If not, you need to account for side to side and front to rear variations. It isn't the lightest loaded tire that fails first. It's the most heavily loaded tire.

[Ramblinboy]

This is a reply to Jammer. I will reduce the psi to 80. This is the pressure Jackson Center uses. It seems the 120 torque setting is okay. I had the trailer weighed yesterday - it came in at 8,380 lbs. The tires fit fine and performed well on a 2 day trip home from a caravan in FL (the tires were installed in Palm City FL and we live in suburban Nashville). There are no fit problems I can see. The chrome trim on the edge of the wheel well is close to the tire and a guy in our caravan who had the same thing done to his trailer removed it from the well, trimmed it with a shears and reinstalled it. I plan to do the same thing (I am not sure it is necessary but I respect his judgment). I noticed that the stabilizers have to reach a little further when I crank them down but that is all. I probably will lose the use of my BAL X-Chock stabilizer because it doesn't close to the reduced distance between the tires and will have to find a substitute. I also plan to put a TPMS sensor on each of the tires. Two tire problems on the interstate are two too many for an old timer like me.

[paiceman]

I made the switch from GYM 15" on our 30' Flying Cloud to Mich 235x75x15 LTX with max tire pressure on the sidewall of 50#. I took the trailer for a test on the interstate empty. The trailer hit a patch of interstate and started to bounce so bad I had to slow it down to get it to stop, I was going 70 mph. I pulled into a rest area to see if she had thrown a wheel weight, had not. So I suspect too much tire pressure. Anyone else run into this with these tires and if so what tire pressure do you run?

Thanks

[SteveSueMac]

I made the same switch on my 27FB. How much does your trailer weigh and is that a tri-axle unit?

I go with the 50# setting and have had no problems like the one you mention.

[xrvr]

70 mph? Still should not have been bouncing. How is your hitch setup. WD and sway? Jim

[r carl]

Are there shock absorbers on your camper?

[m.hony]

I can't tell a difference in the trailer ride whether I have 50 psi (what I've always done) or 65 psi (what the tire placard says).
I can't tell a difference in stuff inside moving around, either.
I can, however, feel that the trailer has less rolling resistance at the higher tire pressure.