Tire Pressure and Torque

[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?

[m.hony]

The tire placard on the street side of the trailer says 65# doesn't it?
That's what I would go with.

[minke]

The tires will have a maximum (cold I think) tire pressure on the side. See also XPS Rib | Michelin Tires

I don't know about appropriate torque.

[SteveSueMac]

This is why those placards have to be updated when you update gear like that.

I would check the sidewall of the tires and go to max pressure, though there are charts that get more specific based on the weight of the trailer. Folks who are more expert on this than me have posted in several threads about this. Try searching for Michelin (probably too many threads, sorry) and you'll find links to those charts.

I don't know about torque on the lug nuts.

Wondering if folks who have the Eddie Bauer version with the 16" wheels can shed some light on that. Anything specific in the user manual there?

[Cardinal283]

This is coming from a former employee of Firestone... Do not use the pressure rating on the sidewall of the tire. That is only the MAXIMUM that tire can hold without risk of damaging the tire from the internal pressure. It has nothing to do with the proper tire pressure for your trailer. The trailer manufacture is the one who decides what is the appropriate tire pressure. They do this by taking into consideration the size tire (sidewall height, tread width) and the weight of the trailer. The idea is to come up with a pressure that keeps the sidewall stiff enough to prevent excessive flexing as it repeatedly loads and unloads the sidewall when it rotates and comes closer to the road. Excessive flexing will cause heat buildup in the sidewall and cause failure. They also want to make sure that the tread is in full and EVEN contact with the road across its entire tread. Too much pressure and the center of the tread will wear out. Too little and the edges will wear out. Excessive pressure will also cause a stiff ride. Airstream rivets don't tend to like stiff rides. When you change the tire size on your trailer you change the formula for the proper tire pressure, so consider that when you go with something different than original sizes. Remember that regardless of who the tire manufacturer is they have no idea what you are putting the tire on. They have no idea the weight of the trailer. Thus they have no way of knowing what the proper tire pressure for your trailer is. Only what the maximum that tire can hold without damage from the pressure. The easiest way to tell is use the original size tire (or very close as changes in sidewall height and tread width can make the required pressure change) and measure the tread wear on the tire at each edge and at the center to get a baseline. Put some miles on it. Measure it again. If the center is wearing the same as the outside edges then you're golden. If the center is wearing faster - lower the pressure a pound or two. If the outsides are wearing faster then bump up the pressure a pound or two. Repeat this process until you have the correct pressure. If there is some other wear pattern then you have another issue all together. Don't forget that as your weight changes so does the load on the sidewall and how evenly the weight is distributed across the tread.


Torque for the lug nuts - This is two fold. Too little torque and the nuts can back off. Too much and you can damage the threads on the nut. The nut is a softer material than the stud. It is designed to fail before the stud. Studs get damaged when someone over torques a nut, damages the threads on the nut, and reuses the nut. Or they cross thread it. A lug nut will go on entirely by hand. If it doesn't there's a problem. As far as the correct torque once again this can only be determined by the manufacturer of either the trailer or the axle. They know the specific alloy and hardness of the studs and know what the proper torque is. Anyone who gives a specific torque without having seen documentation from the manufacturer is guessing (or going off of something they have used in the past). And they are guessing about your trailer. If a wheel comes off on a trailer they won't be there to help or to repair the damage to the trailer. Contact the manufacturer of the trailer or the axle. Hopefully that helps. I'm sure you wanted to hear something like 65 psi and 130 ft lbs, but I'd rather give you accurate information than misinformation.

[TerraYacht]

Cardinal 283 has posted the best summary of tire pressure issues I have seen in a long time.

Although the posted pressure on the placard may not be 100% accurate if you change brands of tires, it will usually only be a few pounds different, if any.

The 19.5" tires on my moho take 90 to 95#, depending on location, and the 6 of them are supporting 18,000# maximum. I would be surprised if the placard has such a high pressure spec.

A short article covering tire pressures is http://www.tirerack.com/tires/tirete...e.jsp?techid=8

Not too that overtorquing the lug nuts can warp the backing plate or brake components that the lugs are seated in.

[SteveSueMac]

Wow! Thanks, Cardinal - I stand corrected and apologize for the incorrect info I provided the OP.

So in the OP's case, the 16s likely can take more than 65PSI but you'd suggest 65 if that's on the placard?

Likewise, the Michelin 15s I put on my trailer (in place of the GYMs) say 50PSI max on the sidewall, but you still would suggest 65PSI?

Not being argumentative here - I just want to be sure I really understand. The Tire Rack article seemed to read that way to me as well.

[Bill M.]

I think that is too much torque.

[m.hony]

I would think the tire placard on the side of the trailer is for trailer tires or 8 or 10 ply load range E tires that will handle 60-80 psi.
Are your 15" Michelins passenger car tires or light truck tires?

[SteveSueMac]

Originally Posted by m.hony

I would think the tire placard on the side of the trailer is for trailer tires or 8 or 10 ply load range E tires that will handle 60-80 psi.
Are your 15" Michelins passenger car tires or light truck tires?

The placard was with the original GYM ST15 tires which have a 65PSI max (and that's where I kept them). I installed the Michelin LTX M/S2 15s whose sidewall says 50PSI max which is where I keep them.

I have to find the thread where I talked about updating the placard because I seem to recall a standard requiring a new placard if you change OEM tires...let me see if I can dig that up soon.

I'm getting confused and don't want to give out bad info. :-/

[Cardinal283]

Originally Posted by SteveSueMac

Wow! Thanks, Cardinal - I stand corrected and apologize for the incorrect info I provided the OP. So in the OP's case, the 16s likely can take more than 65PSI but you'd suggest 65 if that's on the placard? Likewise, the Michelin 15s I put on my trailer (in place of the GYMs) say 50PSI max on the sidewall, but you still would suggest 65PSI? Not being argumentative here - I just want to be sure I really understand. The Tire Rack article seemed to read that way to me as well.

Steve,

I would definitely use the plaque as a starting place. I say starting place because you may have added or subtracted some weight to your trailer. They will usually be dead on within a few psi. Check your tire wear and adjust accordingly.

Under no circumstance should you ever exceed the pressure rating on the sidewall of the tire. If your tire says "50 psi max" and your plaque says 65 psi then you have the wrong load range of tire on your trailer. You need to move up to a higher load range. Higher load range tires will have more plies in them and made from higher quality materials. They can handle higher loads and thus require a higher pressure.

It is important to note that the tire pressure rating on the sidewall is cold tire pressure. That means that the vehicle should not have been driven for at least 3 hours. Air is an interesting gas and expands and contracts quite a bit within the range of temps a tire experiences. This is why newer vehicles are using Nitrogen instead of air. It is much more stable with regards to expansion with temp. Supposedly it also is less likely to permeate the rubber over time than air. Not sure how much that would affect anyone if they are actually checking their tire pressure regularly like they should.

[SteveSueMac]

Ok - I can't figure out how to provide the link from my iphone but here's the "share by email" version. I had asked (toward the en of the thread mentioned below) about updating the placard based on the DOT standards. You can read more in that thread.

I am not going to have these at less than 50 - but am curious about whether I should inflate ABOVE 50? 65 would be 130% of max. That just doesn't sound right?

Shared post from 'Airstream Forum' by BlackAces from thread 'Michelin LTX 235/75R15 XL Upgrade?':



Lots of useful information about replacement tires, including plus sizing, in the manual referenced below. On subject you will find an example of an Auxiliary tire information label in appendix A - page A4.

http://www.tiresafety.com/images/Tir...t%20Manual.pdf

BA

Shared via AIR Forums.


Sent from my iPhone

[SteveSueMac]

Originally Posted by Cardinal283

Under no circumstance should you ever exceed the pressure rating on the sidewall of the tire. If your tire says "50 psi max" and your plaque says 65 psi then you have the wrong load range of tire on your trailer. You need to move up to a higher load range. Higher load range tires will have more plies in them and made from higher quality materials. They can handle higher loads and thus require a higher pressure.

On this point I did a LOT of research to be sure I understood the load issues with using a passenger tire instead of a special trailer tire. The LTX M/S2 15" is rated at 2183 pounds at max pressure (50 PSI). The DOT standard I referenced says you have to derate that by 10% when used on a trailer. So that's 1984# at 50 PSI. That's 7936 total load capacity for my 4 tires which exceeds the GVWR of the trailer. I also have weighed the trailer at CAT scales fully loaded for camping and come in at 5880# which leaves 25% headroom on the derated load capacity.

(That's all from memory so I may be off a digit here or there).

It seems to me (though I could be wrong) that the placard from the factory HAS to assume the GYM ST tires (which are I think 2450# load at 65 PSI - or 9800# total load capacity - which exceeds the axle capacity or GVWR of 7600#). The Michelins, derated per the DOT standard have a total capacity of 7936# at 50 PSI - which also exceeds the GVWR of the trailer and is much higher than the actual weight of the load of the trailer in full camping mode).

I had forgotten how head-swimming this topic gets! :-)

[rodsterinfl]

There is a chart made by michelin to adjust the tire pressure to the specific load they are carrying. I know that I garnered some criticism at one time about this point but I believe Michelin knows more about tires than I certainly do or even most dealers. The dealer set you up with the "maximums" of both torque and pressure. The placard assumes that you are using the same tires and quotes the psi for a trailer tire and they are usually to be used at full psi.

This summer I had a situation that I had to deal with on my wheel lug bolts. They were torqued to 120lbs but one of them started turning and ruined- had to be replaced. Another ALMOST came off as well. I was advised to take it to no more than 100 ft lbs and add thread-ease to my lugs. I am fine tuning my tire pressure (MS/2 not Ribs) using the michelin load/psi chart and the TPMS temp/pressure readings. Interestingly on my last trip, the front tires run warmer by 4 degrees. Also, the side with the sun was 2 degrees hotter - all with the same pressure. Supposedly by the chart you can determine by distance driven, temperature and PSI, the optimum air pressure that allows for heat dissipation and correct tire "squat" for the load. I ran the MS/2 tires (rated to 80psi) at 57psi and recorded the temps and ambient temp. They ran 7 degrees hotter than ambient.

[mefly2]

80 psi on the placard for our Michelins on the EB upgrade wheels.

[SteveSueMac]

Originally Posted by mefly2

80 psi on the placard for our Michelins on the EB upgrade wheels.

Mefly - what does your manual say about torque?

[Ramblinboy]

Thanks for all the posts. As usual, I am amazed at the wealth of knowledge in the Airstream community. I called Jackson Center and they told me that they use 80# psi and torque at 125-45 for my new tire configuration. It looks like I am in the right ballpark.

[gmw photos]

Originally Posted by Ramblinboy

Thanks for all the posts. As usual, I am amazed at the wealth of knowledge in the Airstream community. I called Jackson Center and they told me that they use 80# psi and torque at 125-45 for my new tire configuration. It looks like I am in the right ballpark.

That torque value sounds high to me. In the 2014 Ed B owners manual ( page I-2 ), A/S specs 100 ft-lbs for steel wheels, 110 ft-lbs for aluminum wheels ( same for 15" or 16").

That matches all the charts I have hanging on the wall in my garage. But hey....what do I know ? ( not much, most of the time )

EDIT: google Airstream owners manual, they have them online as PDF's

[Jammer]

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?

I have two conclusions and a question.

Conclusion first. You have good taste in tires insofar as you have chosen the most expensive tires available that will fit your trailer.

Conclusion second. You are exceeding the sidewall max pressure which is 80 PSI. Not a good thing. Indeed Michelin recommends around 50 PSI for your situation, see: http://www.rvtirepressure.com/assets..._Inflation.pdf

I'm assuming your trailer weighs around 8500 pounds with 800 pounds of tongue weight.

A question. How do those fit? Any tire rub against the wheel wells?

[nickmeloy]

Originally Posted by Cardinal283

... Air is an interesting gas and expands and contracts quite a bit within the range of temps a tire experiences. This is why newer vehicles are using Nitrogen instead of air. It is much more stable with regards to expansion with temp...

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.