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mike28 · 02-27-2016, 05:42 AM

What is the proper inflation for the 16" Michelin tires on a dual axle trailer with a gross max weight of 9100 lbs? I get all kind of suggestions.

switz · 02-27-2016, 08:50 AM

We run 73 to 75 psi with the trailer at 9,200 pounds. The axles are only supporting just over 8,050 pounds. My scale numbers are below:

Front.....2,032...2,042

Rear......1.921...2.062

Street rear weight is less since the 6 gallon tank water heater was replaced with a Truma "AquaGo comfort" instant on water heater.

The Michelin load tables for the LT225/75R16 tire show 70 psi = 2,440 pounds and 75 psi = 2,560 so 72.5 psi = 2,500 pounds. At 80 psi = 2,680 pounds and 65 psi = 2,335 pounds. One selects the safety factor they are comfortable with when airing their tires.

paiceman · 02-27-2016, 10:16 AM

Run ours at 73# - 30' FC

Gene · 02-27-2016, 12:01 PM

I'm at 72 lbs. now with Load Range E, LTX M+S2 16" Michelins. Over pressuring is better than under. You did not write what tire you have. It may matter.

I use a tire tread gauge to check how the tires are wearing and make adjustments accordingly. Too much pressure, center wears faster; too little pressure, outer edges wear faster; uneven wear, tire out of balance. Of course the tire has to be able to support the weight too (more pressure, more weight).

Call Michelin and ask them. It'll probably take some time for them to figure out because their tables don't list trailer use. Some people who answer the phone know a lot more than others.

Gene

Siegmann · 02-27-2016, 01:18 PM

In my opinion, the closer the pressure is to max, that doesn't give your rig a rough ride, is what protects the tire the best.

I always wanted to try an experiment. Air the tires up to max. Place several small paper cups with water around the rig. Drive for some reasonable distance, at highway speeds, down a typical/average road. Check the cups. Drop the tire pressures down to whatever your analysis indicates would be OK for your load. Repeat test drive. Check the cups. Air the tires up to an intermediate pressure that you think might be the best compromise pressure for smoothness of ride and load support. Repeat test drive, as needed.

mike28 · 02-27-2016, 04:44 PM

Thanks for your replies. I was told about 65 lbs and it looked way too low. The guys at Discount Tire suggested 75 lbs which is right in the range you all suggested. Thanks again! This is totally new territory for me with the LT tires.

CapriRacer · 02-29-2016, 07:43 AM

One way to tell if you've got the right inflation pressure is with pressure buildup:

Check the pressures immediately before starting out on a long highway trip - one with continuous high speeds. Record the pressures if your memory is like mine!

Then after an hour and a half, check them again.

You do NOT want more than a 10% buildup. If you have more than 15%, you need to do something IMMEDIATELY! For the duration of the trip - SLOW DOWN - but you will need more load carrying capacity - more pressure and/or a larger tire. You will need to do this as soon as possible.

If you are between 10% and 15%, you need to slow down, and figure out what you want to do, but the need is not as critical and can wait - not until the tires wearout (or age-out), but a trip or 2 is OK.

Also, this test is NOT a guarantee that the tire size/pressure is OK, but excesssive buildup tells you it is not!

switz · 03-01-2016, 11:14 AM

CapriRacer:

So I set the 15" Michelin LTX (P) 235/75R15 XL tires to 44 psi when it was 35 degrees in the morning. Later that day the air temp was around 75. The TPMS was reporting tire pressures had increased to 51 psi (maximum side wall pressure is 50 psi) while running 55 mph. Three tires carry an average of 1,250 pounds and the fourth is carrying 1,376 pounds due to the design of the 23D. I have seen less pressure increase when the starting air temperature for the day is fairly constant going thru the day.

Should I have stopped and let two or three psi out of the tire. I use a digital LongAcre tire pressure gage?

SteveSueMac · 03-01-2016, 05:11 PM

Quote:

Originally Posted by switz

CapriRacer:

So I set the 15" Michelin LTX (P) 235/75R15 XL tires to 44 psi when it was 35 degrees in the morning. Later that day the air temp was around 75. The TPMS was reporting tire pressures had increased to 51 psi (maximum side wall pressure is 50 psi) while running 55 mph. Three tires carry an average of 1,250 pounds and the fourth is carrying 1,376 pounds due to the design of the 23D. I have seen less pressure increase when the starting air temperature for the day is fairly constant going thru the day.

Should I have stopped and let two or three psi out of the tire. I use a digital LongAcre tire pressure gage?

Not attempting to reply for an actual tire engineer - but - my 15" Michelins carry about 1500# each (haven't had individual wheels weighed). I start cold at 50 PSI and according to my TPMS never go above 55 PSI (10% over cold start) and 30 degrees above ambient temp (if it's 80 degrees outside, they'll go to 110 degrees after about an hour on the road).

I've read (Goodyear tables I believe) that you don't let air out even if you start at max pressure cold. It's expected to increase with use.

Why your increase in pressure (16% over your cold start) is so much higher than mine - while carrying less weight per tire - is a mystery to me.

tjdonahoe · 03-01-2016, 05:22 PM

I am going to try 73 lbs in my new 16" michelins, on the way to california in 3 weeks.....

**Action** · 03-01-2016, 07:20 PM

My guess is the starting tire pressure for switz is too low. The tires heat up because of internal friction. Lower tire pressure creates greater internal pressures than higher tire pressure. (It is possible the load on the tire is too high for the load capacity of the tire. I assume this is not the case.)

The max cold pressure is 50. All tires will exceed the max pressure when hot if they start at or near the max. And setting pressure on a hot tire isn't how tires are designed. Letting pressure out of a hot tire is not a good idea either in my opinion.

>>>>>>>>>>>>>>>>>>>Action

SteveSueMac · 03-01-2016, 07:37 PM

Action - these are the P-rated Michelins. De-rating them for use on a trailer they have a capacity of 1985# (I think at 44PSI but I always go to max of 50). If Switz is only seeing about 1300# on those tires, he's still got 35% headroom on the (de-rated) load.

I wonder if you're right about the PSI?

Switz - you might experiment with 50 PSI cold and see if that only increases PSI by 10% after a hour...

I forget whether you have a TPMS or not and if you do, if it monitors pressure and temp...

switz · 03-01-2016, 07:43 PM

Have the Dill 1506-453 TPMS system. Max load in these 15" "P" XL Michelins is at 41 psi so going on up to 50 psi just stiffens the sidewalls from what I have read. Andy at CanAm suggested the 44 psi as the starting point for this tire installation on both the 25FB and the 23D. I also increase the Mercedes tow vehicle tire pressure to 44 psi from 32 front and 39 rear per his suggestion.

**Action** · 03-01-2016, 08:19 PM

If it were me, I would bump the pressure by 2 or 3 pounds cold on the next trip and the monitor the pressure rise. If the pressure rise percentage decreases on the hot tires you might have discovered something.

It couldn't hurt much.

>>>>>>>>>Action

CapriRacer · 03-02-2016, 06:16 AM

Quote:

Originally Posted by switz

CapriRacer:

So I set the 15" Michelin LTX (P) 235/75R15 XL tires to 44 psi when it was 35 degrees in the morning. Later that day the air temp was around 75. The TPMS was reporting tire pressures had increased to 51 psi (maximum side wall pressure is 50 psi) while running 55 mph. Three tires carry an average of 1,250 pounds and the fourth is carrying 1,376 pounds due to the design of the 23D. I have seen less pressure increase when the starting air temperature for the day is fairly constant going thru the day.

Should I have stopped and let two or three psi out of the tire. I use a digital LongAcre tire pressure gauge?

First, it is never a good idea to let pressure OUT of a hot tire. Not only is the elevated pressure telling you something, it might be keeping you from a catastrophic failure.

Second, the max pressure listed on the sidewall of a tire is a maximum COLD usage pressure. It is expected that the hot pressure will buildup and perhaps be more than the max pressure listed on the sidewall.

Third, when doing these calculations, you have to remember that ambient temperature affects things. In this case, the ambient temperature increase from 35 to 75 should have resulted in about a 4 psi buildup, so the starting cold pressure should have been recalculated from 44 psi to 48 psi, and the operating pressure buildup to 51 psi is only 3 psi - and since that is less than 10%, that is good.

Lance M · 03-02-2016, 06:35 AM

Capri,
Can you comment on the effect of low ambient temperature in the morning and high ambient temperature in the afternoon, as is often the case in the desert SW? I have often left out in the morning with the temperature 38 degrees and afternoon highs may be near 100 degrees. How does this relate to the 10% rule of thumb? The higher temperature must account for some of the pressure increase, yes?
Thanks

switz · 03-02-2016, 08:19 AM

Is there a table somewhere or a rule of thumb to use to estimate the tire pressure rise due to just the day getting warmer? An off the cuff observation of post 15 is that there is a 1 psi increase in tire pressure for each 10 degrees Fahrenheit. I presume that the tires in question are in the shade.

Thus a day that started at 55 and went to 115 (like in the south west) one would expect the shaded tire pressure to increase 6 psi.

The Dill TPMS does show higher temps and pressures for the tires on the sunny side of the trailer when driving down the highway. I can see similar results on the built in TPMS of the Dodge 2500HD.

**Action** · 03-02-2016, 10:07 AM

As long as we are asking questions, and I live in the South West like some other posters do.

Does the road temp make a difference? So in June the ambient can get to 115 (or a little higher) however the asphalt can be 10 or 15 degrees higher than that. (May be more however I don't check that) Since it is the road surface is where my tires dwell is that an issue for any concern as far as inflation?

My current strategy is to check and fill if needed the tires to any and all vehicles very early in the morning. Even on a 115 degree day that starts out at over 100 the driveway and tires have not been heated up so I use that time to check. Typically I check all vehicles once a month when I am in town. As the seasons change there is some adjustments in pressure based on ambient temps.

>>>>>>>>>>>>>>>Action

4RXLA · 03-02-2016, 06:58 PM

I run mine at 70psi with a weight of 7500lbs.

**jcanavera** · 03-02-2016, 07:52 PM

I'm running 80 psi on my 30' Classic Slideout. Weight with normal camping load is about 8600-8700 lbs. With fresh water tank full, I'm at the 9100 lb limit. I using the Michelin 16" LTX MS2 tires. This particular trailer was the heaviest trailer that Airstream built on a tandem axle. Personally I'd rather error on the higher side with the air pressure. I've not seen any negative issues structurally, running at this pressure.

Jack