Tire Pressures and Tire Temperature

[overlander63]

The recommended tire pressure for the 16 inch replacements is 70 PSI.

[guskmg]

Where did 70 PSI come from? Airstream recommends 80 for ST or LTX E rated. They have the most liability at stake.
Guskmg

[overlander63]

Originally Posted by guskmg

Where did 70 PSI come from? Airstream recommends 80 for ST or LTX E rated. They have the most liability at stake.
Guskmg

That's what happens when I use my tablet to post. I hit "8", but "7" showed up.
It is supposed to be 80PSI.

[Wingeezer]

When I switched to 16" Michelins two years ago, I got very confused about all the recommendations on best pressure to run!

In the end I settled on 75psi as it seemed a good average of what everyone was running and I liked the fact that it was little below the tires max rating.


Seems to have worked fine for me so far on two cross country trips and a few shorted ones and I will probably stay with it!

I'm not seeing any real wear pattern at all on the tires yet that would indicate either under or over-inflation for this application, and in fact they still look brand new!

Brian.

[slowmover]

Originally Posted by Msmoto

Having just installed new 16" wheels on my 2015 Serenity, along with the Firestone Transforce LT225/75R16, I am attempting to decide on the correct tire pressure and how to determine this.



In ambient temperatures of 80º F, at no time was the tire more than warm. Even with 30 - 40 mph sideways gusts of wind over several hundred miles, the tires and wheels remained only warm to my hand, never hot enough to prevent touching.



My question is, can one determine the correct tire pressure based upon how arm the tire gets in use? It would seem to me, if the tire were under inflated, it would become much warmer, way to hot to touch. Correct inflation would result in the coolest running temperature.



Mine are at 65 PSI currently and I am thinking this is the correct pressure, but would like the experience of others with 16" wheels/tires.

You're looking to set a numerical baseline. If you wish to be thorough, then, with full fuel and the truck loaded for a long trip, make three passes across a Cat Scale. The trailer should also have full propane and fresh water plus gear/supplies for extended travel.

Pressure tires to sidewalk max on TT and the Dodge to within door placard numbers.

Search and use the Ron Gratz chart ( I've posted it several times here [originally from a 2010 thread at Woodalls] and it allows for an examination of WD loads.

If the hitch needs adjustment, then this is the time to do it.

The final check is to weigh the combination with corrected WD applied, wheel by wheel. Same day as the above. The truck will probably show individual weights as equal across each axle

The TT will not.

The reference to use is the Bridgestone and RV Safety Foundation pdf at that companies website titled How To Weigh an RV.

This will entail a good number more passes across the scale. The re weighs are cheap.

If the across axle weight discrepancy is large, it may be worth trying to shuffle the weight around. On the axle or within a foot or two. Avoid the trailer ends.

The ideal is no more than about .85 of sidewall maximum per tire.

Check the tire pressures when cold the next morning. Drive 1-1.5/hrs steady state (cruise control) and have a preambles stop at an Interstate parking area or rest area with a long runway . . use as little brake as possible to come to a full stop.

Assuming bearing and brake adjustments were properly made, one is looking to see a pressure rise of 10% or less in all tires. 5-7% is ideal.

With WD at a good point, with tire pressures at recommended numbers, and if any changes necessary are made

you now have the numerical baseline from which to make further changes if you deem them worthwhile. A default setting.

[CapriRacer]

Well, lots of good comments. Lots of not so good comments. So I'll add mine.

The one thing no one has said is: After you've gone through all the weighings and the charts and the calculations and come up with a number, how can you verfiy that is correct? The pressure build up test.

Set your cold pressures. Drive on the freeway for 45 minutes to an hour, then measure the pressures. You should get no more than a 10% build up. If you get more than 10%, you need to add air. If you get more than 15%, you need to take immediate action - driving slower, add load carrying capacity( more air, higher load range, bigger tire).

If you are UNDER 10%, then drive another 45 minutes to an hour. It takes about an hour and a half to get the tires to stabilize, that's why 2 readings. An early one to prevent going too far, and to see where you are headed - and a second one to get a final reading.

Please note: Freeway driving means open country - and the speeds you normally tow. If you've done your homework, this should just be a confirming test - or if you suspect you have a problem, this might confirm it for you.

[HowieE]

Originally Posted by CapriRacer

Well, lots of good comments. Lots of not so good comments. So I'll add mine.

The one thing no one has said is: After you've gone through all the weighings and the charts and the calculations and come up with a number, how can you verfiy that is correct? The pressure build up test.

Set your cold pressures. Drive on the freeway for 45 minutes to an hour, then measure the pressures. You should get no more than a 10% build up. If you get more than 10%, you need to add air. If you get more than 15%, you need to take immediate action - driving slower, add load carrying capacity( more air, higher load range, bigger tire).

If you are UNDER 10%, then drive another 45 minutes to an hour. It takes about an hour and a half to get the tires to stabilize, that's why 2 readings. An early one to prevent going too far, and to see where you are headed - and a second one to get a final reading.

Please note: Freeway driving means open country - and the speeds you normally tow. If you've done your homework, this should just be a confirming test - or if you suspect you have a problem, this might confirm it for you.

That is one of the best posts i have seen. Gets noted here and a Thanks to you

[ckottum]

CarpiRacer, does this mean that if we run our Michelin 16" LTX tires on our Airstream at 60 psi, rather than the 80 psi maximum pressure indicated on the sidewall, that is a correct pressure if it passes your pressure test procedure?

That seems to be in conflict with another tire engineer who has recently cautioned here that any tire used on a multi-axle travel trailer with lowered pressure is more likely to experience tread separation from sideway scrubbing when turning the trailer, so we should always use the maximum sidewall indicated pressure.

Or are you suggesting we should always use the maximum sidewall indicated pressure, and then use your pressure test procedure to ensure it is enough? I suppose the two tire engineers would be in agreement then?

The correct tire pressure for our Airstream remains unclear to me.

cheryl

[Phoenix]

Just my opinion: Airstream, Discount Tire, Costco and others recommend "maximum sidewall pressure" for trailer tires. For load range E tires, that's 80 psi.

I have ridden in our 2005 19' Bambi at highway speeds, with OEM GYMs inflated to 65 psi and Michelin XPS Ribs inflated to 80 psi; and I could tell no discernable difference in ride.

Our tires have been inflated to maximum sidewall pressure for 10 years -- no calculations necessary...

[BoldAdventure]

Yes, that's the confusion I'm getting here, if I set mine to 80psi cold, then get 10% I'm now over max. But if I set to 73psi + 10% that'd be 80psi.

[jcanavera]

Keep in mind however, that tires filled to max cold sidewall pressures are engineered to handle higher pressures generated by road use. So for all intents that max pressure rating is not your goal to meet when the tire heats up. It's a guide as to the load capacity of that tire at cold temperatures. Dependent upon air and road temps it is entirely feasible to run pressures that exceed max inflation. What you don't want is an overload situation where air pressure is insufficient to carry the load. That's why we get the blanket statements from Airstream and Tire retailers to use max sidewall pressure. That insulates them from liability somewhat since they have no idea of the load you will subject these tires to.

Jack

[BoldAdventure]

Originally Posted by jcanavera

That's why we get the blanket statements from Airstream and Tire retailers to use max sidewall pressure. That insulates them from liability somewhat since they have no idea of the load you will subject these tires to.

I assumed this much. It's pretty common.

[HowieE]

Originally Posted by Phoenix

Just my opinion: Airstream, Discount Tire, Costco and others recommend "maximum sidewall pressure" for trailer tires. For load range E tires, that's 80 psi.

I have ridden in our 2005 19' Bambi at highway speeds, with OEM GYMs inflated to 65 psi and Michelin XPS Ribs inflated to 80 psi; and I could tell no discernable difference in ride.

Why in Gods name would you do that? If a C rated GYM could run at 65 lbs. Why would you run an E rated tire any higher under the same load.

Get the trailer weighted and set the tires to the inflation chart not to the recommendation of someone that may not even be able to spell inflation.

[Phoenix]

HowieE, I assume the 65 psi inflation pressure that you reference is for a LR-D GYM. On your 34-foot, triple-axle Excella, the per-tire load is about 1,500 pounds.

I have a 19' Bambi that weighs 4,500 pounds on a single axle; so my per-tire load is about 2,250 pounds, which is 50% higher than the tire load on your Excella.

Note: Weights are approximate due to differing tongue weights and the unknown number of barbells and anvils we may both have hidden in our Airstreams.

In the first few years of ownership, three of six ST tires failed on our Bambi. The two GYMs were LR-D, inflated to 65 psi; and the LR-E Maxxis tire was inflated to 80 psi.

Four years ago, we switched to 16" wheels and LR-E LT tires, which are inflated to 80 psi; and in the past 25-30,000 miles since switching, we have had absolutely no tire problems.

For me, this is enough proof that ST tires are unsuitable for my Bambi, and 80 psi is the proper tire pressure (for LR-E tires).

I should note that we live in the desert southwest where summer temperatures often reach 118+. Others who travel in cooler climes and have lower per-tire loads may have better luck with ST tires and/or lower tire inflation pressures. However, the Airstream Tire Failure Poll would seem to indicate otherwise, with an approximate 50% failure rate reported for ST tires, 75% of which were inflated to the maximum sidewall pressure.

[frankrightbrain]

Originally Posted by Re-Pete

Can anyone post links to a thread/s on how to weight a TT (Airstream) including the individual tires? I've not done this before, and am a bit intimidated by the process.

Configure your Airstream as if you are going camping and if your area has a Farmers Coop call and ask if they have scales. If no Coop then call your local solid waste landfill who will have scales. Call ahead and ask if they can weigh your trailer and if so, pull your tow vehicle forward and off the scale leaving just the AS tires on the scale ramp. This will give you the actual weight adjusted for your hitch displacement. If your hitch/TV arrangement doesn't sit level, as mentioned in a previous comment, you may call your State's DEPARTMENT OF motor Vehicles and ask if you can weigh your AS at a DMV weigh station near you. If there is a nearby Airplane repair shop they should be able to weigh your AS for a fee.

[BoldAdventure]

Originally Posted by frankrightbrain

Configure your Airstream as if you are going camping and if your area has a Farmers Coop call and ask if they have scales. If no Coop then call your local solid waste landfill who will have scales. Call ahead and ask if they can weigh your trailer and if so, pull your tow vehicle forward and off the scale leaving just the AS tires on the scale ramp. This will give you the actual weight adjusted for your hitch displacement. If your hitch/TV arrangement doesn't sit level, as mentioned in a previous comment, you may call your State's DEPARTMENT OF motor Vehicles and ask if you can weigh your AS at a DMV weigh station near you. If there is a nearby Airplane repair shop they should be able to weigh your AS for a fee.

lol, or just go to any CAT scales at any one of the dozens of truck stops in the country.

[HowieE]

Originally Posted by Phoenix

HowieE, I assume the 65 psi inflation pressure that you reference is for a LR-D GYM. On your 34-foot, triple-axle Excella, the per-tire load is about 1,500 pounds.

I have a 19' Bambi that weighs 4,500 pounds on a single axle; so my per-tire load is about 2,250 pounds, which is 50% higher than the tire load on your Excella.

No actually the Michelin tires on my 8,900 lbs 34 are inflated to 45 lbs. and that is 5 lbs more that the chart calls for. I run then slightly high so if I have a flat I can run in and still have enough pressure in the tires to carry the load.

I am going to assume you are running 225 75 16 E and if that is the case your tire pressure should be 60 lbs for that weight. Since Michelin does not make a D rated tire and a C rated would be pushing is at 4,000 lbs.

[frankrightbrain]

Originally Posted by BoldAdventure

lol, or just go to any CAT scales at any one of the dozens of truck stops in the country.

Lol, that works too. I like options. Seems you have all the answers. You win the Internet for 5 minutes.

[rodsterinfl]

My question is, can one determine the correct tire pressure based upon how arm the tire gets in use? It would seem to me, if the tire were under inflated, it would become much warmer, way to hot to touch. Correct inflation would result in the coolest running temperature.

Absolutely. This conversation is ongoing on this forum. I do not know your tire brand info but I have Michelin MS/2 16" and there is a chart for both the MS/2 and Rib. That chart, which I have posted several times is based on load per axle. Contrary to popular belief, the chart for the E rated 16" tires goes as low as 30 PSI up to 80 PSI for the max load. Temperature sensors can be used to dial in the best PSI. If tires are too low, the temperature rises quickly and stress is on the sidewall. Too much pressure for the load and the pressure is transferred to the tread and the radial tire footprint is misaligned. It is not good either way. I have never run tires at max PSI on any vehicle. It rides rough and violates manufacturer guidelines AND gives no leeway for the tire.

CAT Scales: In the "RV Handbook 4th Ed. by Dave Solberg, p.73, they provide a diagram for trailer weighing showing how to use CAT scales. "pull up until the truck front axle mirrors are past the end of the first scale plate. The rear axle and trailer jack should then align with the second plate while the trailer axle(s) are on the third plate. Small trailers may have to adjust position."

[Tater]

I've had 16 " Michelin s on our 30' Classic for 2 years and about 10000 miless. I run 80 psi cold.