Tow vehicle Tire Pressure

I have been on the phone with Michelin about my tires going around in circles (no pun intended) getting no answers.
On my tow vehicle I have Michelin LT 275/16R/18  MS.  On the sidewall it gives the load range as 123/120 @80PSI.  Michelin says the tire does not say this.  My dealer say Max pressure I should put in is 35 PSI.  Does anyone know what the 80 PSI refers to.  I know the 123/120 is for a dual or single set up.  When fully loaded and towing the RV should I be @ 80 PSI??

The Cujman 

On the sidewall it gives the load range as 123/120 @80PSI.

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The sidewall states the maximum load the tire is designed to carry and the psi needed to support that max load.  Usually it states actual lbs or kilograms, but a value called Load Index or Load Range is also displayed.  Neither of these is a recommendation for the actual pressure needed for your vehicle, and no modern tire manufacturer will give such a recommendation (fear of lawsuits). Any recommendation will come from the vehicle manufacturer and be shown on the Tire & loading placard for the vehicle.

123 and 120 are the Load Index values that correspond to 3417 lbs and 3086 lbs (respectively). Those values are achieved when the tire is inflated to 80 psi (lower pressure reduces the load carrying capability). You can view a Load Index chart at https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35


This article explains all the things displayed on a tire sidewall.https://www.discounttiredirect.com/learn/reading-tire-sidewall

I'm not sure what your tire dealer based his 35 psi on, so can't comment on its validity, but its ok to run a tire at less than its max load psi IF the actual load is less. Without knowing what the actual or rated load of the axle is, the optimal psi is unknown.  The axle ratings for your truck are also shown on the Tire & Loading placard (yellow sticker on driver door post).

There appears to be a typo in the tire size in your message. which you list as  Michelin LT 275/16R/18  MS.  That doesn't match any known tire size designation.  It should look something like LT275/75R18, where the 265 is the width, 75 is the aspect ratio, and 18 is the wheel (rim) diameter.  If you can supply the correct information, we can help you find the Michelin Tire Inflation table that matches it.

This will answer your question

https://www.michelintruck.com/assets/pdf/Truck_Tire_Data_Book_Sept2011.pdf

What you need to do is load your tow vehicle up just as you would take it on a trip, hook your fully loaded trailer up and take it to your nearest CAT scale and get the weight on each axle:

https://catscale.com/

Once you've got your axle weights, you can go to your inflation chart and find the correct tire pressure.  The Michelin chart for RVs is here:

https://www.michelinrvtires.com/reference-materials/load-and-inflation-tables/#/

Pretty good background info here:

http://www.rvtiresafety.net/search/label/Load%20Inflation%20table

Thanks for the responses.  Very useful information.  Sorry about the typo it should have read LT275/65R/18 MS.  I should clarify the tires are on my truck not the trailer

The Cujman

There are no 18" tires in the Michelin charts referenced above, and I haven't found one online yet that does have 18".  The latest tables available online fromMichelin are at this site and no 18" there. Not in the Truck Tire Data Book either.


https://www.michelintruck.com/reference-materials/manuals-bulletins-and-warranties/load-and-inflation-tables/#/
https://www.michelintruck.com/assets/pdf/Truck_Tire_Data_Book_Jan2007.pdf

The tire appears to be the LTX A/T 2, which has a max load rating of 3415 @ 80 psi.

Gary:
I attached two pics in a reply but after I sent it the reply just disappeared. I think the file size is too large.  Anyway the Tires are Michelin LT 275/65R 18 MS.  Michelin customer service said I was wrong also.  Don't know what to think now

What truck are these on?  What Load Range?  D?  E?  There should be, as Gary said, a max load at max psi label on each tire.

I found a Michelin Defender LTX MS tire in your size at tire rack.com.   
https://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Defender+LTX+M%2FS&partnum=765R8DLTX&vehicleSearch=false&fromCompare1=yes

This is a load range E,  3415 lbs at 80psi tire.

IF this is your tire, or yours is a LR E, then 80 psi is the max psi for the tire.  What is the actual load on the tires so we can comment on proper inflation.

The 35 psi the tire dealer recommends sounds low, sufficient for only a very light load. The 80 psi max load psi might give a harsh ride, but at least you would know the tire is adequately inflated.  The optimal psi is almost surely somewhere in-between, but you need to get axle weight information to determine that.  If you cannot get a scaled weight for each axle, get the axle GAWR (found on the tire placard on the driver door post) to use as an estimate.  HOWEVER, until somebody locates a tire inflation table for that sie of tire, knowing the actual weight is of no help.

The  tire & loading placard will have the truck manufacturer's recommended psi, which is usually sufficient for a large load or even max truck loading. Use that until you can get actual data to choose a different psi.
I've attached some sample Tire & Loading placards - yours should be similar.

cujman said:

When fully loaded and towing the RV should I be @ 80 PSI??

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As mentioned above, the only way to know this is by weighing your entire loaded rig. CAT (or similar) scales at truck stops are an easy option to do this. Many gravel pits or grain elevators (if you have either of those near where you live) also have large trucks scales, sometimes available for free use by the general public. That's how I weighed my loaded trailer. We have a forum library article here on how to weigh and get the numbers you need (trailer weight, trailer tongue weight, tow vehicle axle weights loaded/unloaded) to help you determine tire pressures and setup of your weight distribution hitch.

The door jamb placard in my Suburban (tow vehicle) recommends tire pressures at 35psi front / 50psi rear for everyday driving, and 45 front / 80 rear for towing heavy loads. That's what I used for awhile, however my towing experience was a bumpy/harsh one. Once I weighed everything properly and compared to my axle/tire load limits, I was able to reduce my towing psi to 43 front / 73 rear. Taking that step + adding a set of rear axle airbags GREATLY improved ride quality while towing.

cujman said:

I have been on the phone with Michelin about my tires going around in circles (no pun intended) getting no answers.
On my tow vehicle I have Michelin LT 275/16R/18  MS.  On the sidewall it gives the load range as 123/120 @80PSI.  Michelin says the tire does not say this.  My dealer say Max pressure I should put in is 35 PSI.  Does anyone know what the 80 PSI refers to.  I know the 123/120 is for a dual or single set up.  When fully loaded and towing the RV should I be @ 80 PSI??

The Cujman

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As someone has already pointed out your tire is most likely a LT275/65R18 LRE Michelin Defender. The MS is not part of its designated size, it just denotes it's good in mud & snow. The LRE is not part of its designated sizer, it just denotes its load rating.

Are you referring to your tires as being the original size? If they are the original size the proper inflation for them is displayed on the vehicle certification label, in the owner' manual and on the tire/load label. That recommended inflation for OE tires is good all the way to the vehicle GVWR unless you have overloaded the rear axle. I doubt very seriously that any LT tire inflated to 35 psi would safely carry the load of your vehicle. Are you sure the OE tires were not passenger tires?


All LT tires have the maximum amount of load they can carry molded onto their sidewalls (3415) and the amount of inflation pressure needed to support that load (80 PSI). Vehicle manufacturers use load inflation charts to tailor recommended cold inflation pressures appropriate for each tire fitment to a vehicle. Individual vehicle tailored values are displayed on every vehicle's federal certification label. 

Thanks again for all of the replies.  I am learning quite a lot.  The tires do say LTX . Nothing about defender.  Not sure what the original tires were.  The replacement tires I bought for my TT I got from a commercial truck tire company.  I think I will go back there and see if they can advise on new tires

The Cujman