Tire Pressure

[Tireman9]

Originally Posted by SBTAR

When I had 5000 miles on my solera noticed tire wear on outside edges of front tires had pressure at specs on the door. Since than inflated them to 80psi cold 10,000 miles on them now,tires look perfect now,thought it was alignment problem. Think it was the lower pressure. I think it's safer to run them at the 80 psi because the tires run cooler. You have a little extra weight carrying capacity and you get better gas mileage because the tires roll with less resistance. The only draw back is you get a little harder ride. Does not matter about how much pressure they are when there hot. Manufacture say 80 psi cold so I sure they figured for heat and temperature increase.

I would say your front axle is loaded heavier than the expectation from the mfg. What are your actual loads on each front tire? Bet we find that the load/infl tables suggest somethnig closer to 80 that the placard inflation.

[OldCoot]

Originally Posted by Tireman9

Bet those tires were bias ply not steel belted radials.

Race car drivers do a lot of things that should not be done for regular highway use.

They were bias ply tires and we also modified the pattern by grooving them for more bite and siped them for cooling.

[Tireman9]

Originally Posted by OldCoot

And it also states "Over-inflation tires make for spectacular explosions". Doesn't make any difference how they got over-inflated. I don't deflate hot tires because it is a pita and requires re-inflation, but if someone wants to do it, it won't hurt a thing. To each his own. I have yet to see a tire manufacture warn against deflating hot tires. If I were on a long trip and the temp and pressure kept rising and the pressure got to a point that "I" considered excessive, I would bleed them off. Truck System Technologies(TST) states: "We recommend you set the parameters at 15% above and 10% below what you typically run in your tires. System Technologies believes to be the safe zone. As for temperature, the monitors are preset at 157' F, a safe setting for all tires, which typically fail between 180-200" F."
So, in my case with a 65# cold pressure and the recommended 15% over cold pressure for an alarm, 10# over or 75# would be setting off the alarm and I would deflate.

You might want to read the top of pg 6 of the Michelin RV tire guide

Do I need to find similar from other tire companies?

[OldCoot]

Originally Posted by tireman9

you might want to read the top of pg 6 of the michelin rv tire guide

do i need to find similar from other tire companies?

no page 6

[Tireman9]

Originally Posted by Mikegjax

A tire's maximum inflation pressure is the highest "cold" inflation pressure that the tire is designed to contain. However the tire's maximum inflation pressure should only be used when called for on the vehicle's tire placard or in the vehicle's owners manual. It is also important to remember that the vehicle's recommended tire inflation pressure is always to be measured and set when the tire is "cold." Cold conditions are defined as early in the morning before the day's ambient temperature, sun's radiant heat or the heat generated while driving have caused the tire pressure to temporarily increase.
For the reasons indicated above, It is also normal to experience "hot" tire pressures that are up to 5 to 6 psi above the tire's recommended "cold" pressure during the day if the vehicle is parked in the sun or has been extensively driven. Therefore, if the vehicle's recommended "cold" inflation pressures correspond with the tire's maximum inflation pressure, it will often appear that too much tire pressure is present. However, this extra "hot" tire pressure is temporary and should NOT be bled off to return the tire pressure to within the maximum inflation pressure value branded on the tire. If the "cold" tire pressure was correctly set initially, the temporary "hot" tire pressure will have returned to the tire's maximum inflation pressure when next measured in "cold" conditions.
A tire's "maximum inflation pressure" may be different that the assigned tire pressure used to rate the tire's "maximum load." For example, while a P-metric sized standard load tire's maximum load is rated at 35 psi, many P-metric sized standard load performance and touring tires are designed to contain up to 44 psi (and are branded on their sidewalls accordingly). This additional range of inflation pressure (in this case, between 36 and 44 psi) has been provided to accommodate any unique handling, high speed and/or rolling resistance requirements determined by the tire and vehicle manufacturers. These unique tire pressures will be identified on the vehicle placard in the vehicle's owner's manual.

Ok lets try and clear up the "Maximum" inflation question.

First all tires have markings identifying the "Maximum" load associated with a "Cold" inflation.

Second, Some tires have a "Safety Warning" that mentions when "mounting" tires you should have a professional do the job and as part of that mounting information safety warning they give a maximum inflation. The reason for this is that if a tire is damaged during mounting or not centered on the wheel before the beads "seat" or the wheel is the wrong size (yep some people make that mistake) we want to prevent an explosion due to improper "seating" pressure against a damaged tire bead.
Once the tire is properly seated the inflation will many times exceed the maximum "seating" pressure but it is OK at that point as the tire is now properly seated on the rim.


If you have questions about I suggest you get a flashlight and sit down and actually read the information on the sidewall of your tires. I did a post just on that topic April 24 2013.

[Tireman9]

Originally Posted by Mikegjax

We always used nitrogen for aircraft tires for several reasons. Pull the following info. from a web site and it might answer some questions.

First is that nitrogen is less likely to migrate through tire rubber than is oxygen, which means that your tire pressures will remain more stable over the long term. Racers figured out pretty quickly that tires filled with nitrogen rather than air also exhibit less pressure change with temperature swings. That means more consistent inflation pressures during a race as the tires heat up. And when you're tweaking a race car's handling with half-psi changes, that's important.

Passenger cars can also benefit from the more stable pressures. But there's more: Humidity (water) is a Bad Thing to have inside a tire. Water, present as a vapor or even as a liquid in a tire, causes more of a pressure change with temperature swings than dry air does. It also promotes corrosion of the steel or aluminum rim.

How is water relevant to a nitrogen discussion? Any system that delivers pure nitrogen is also going to deliver dry nitrogen. Filling tires with nitrogen involves filling and purging several times in succession, serially diluting the concentration of oxygen in the tire. This will also remove any water.

It's certainly simple, although time-consuming, for a tire technician to fill and bleed tires. But most shops use a machine that not only generates almost pure nitrogen by straining the oxygen out of shop-compressed air, but will also automatically go through several purge cycles unattended. Some shops have been charging as much as $30 per tire for this service. I think that's too much. If you're buying a new tire, it should be far less. Still, the nitrogen generator, filling system and technician's time aren't free—the dealer is entitled to some return for that.

So, to answer your specific questions: With nitrogen, your tire pressures will remain more constant, saving you a small amount in fuel and tire-maintenance costs. There will be less moisture inside your tires, meaning less corrosion on your wheels. You will not be able to feel any difference in the ride or handling or braking, unless your tire pressures were seriously out of spec and changing to nitrogen brought them back to the proper numbers.

If the pressure remain more constant (lower) because you have dryer inflation "gas" how will that get you better fuel economy?
It is well documented that lower pressure increases fuel consumption. This is because lower pressure allows more tire flex which generates heat. Heat generation consumes energy which means it takes more effort from the engine to move the vehicle. More engine effort is lower fuel economy.

Sorry the advertising hype isn't supported here.

I have multiple posts on Nitrogen and on fuel economy. Also You tube videos.
Simply search YouTube on "roger marble tires"

[Tireman9]

Originally Posted by OldCoot

Please explain the harm. Extra work I fully understand. If my alarm goes off at 10# excess pressure I just stop and let them cool. TST TPMS recommends 15% over cold pressure as the alarm setting. In my case that's 10#.

Extra work means extra heat. Heat is what kills tires. The damage is microscopic (at first) but never repairs itself.

TPMS are external to the tires so are actually cooled by the air moving around the valve stem. If you have high moisture content your infl will increase more. maybe set the High pressure alert a couple pounds higher.

[Tireman9]

Originally Posted by OldCoot

no page 6

sorry Try pg 7

"Never let air out of a hot tire."

[Tireman9]

Hey folks this has been fun but I have to get up early for some out patient surgery. I hope to be back on line by Tuesday.

Roger

[OldCoot]

Originally Posted by Tireman9

Extra work means extra heat. Heat is what kills tires. The damage is microscopic (at first) but never repairs itself.

TPMS are external to the tires so are actually cooled by the air moving around the valve stem. If you have high moisture content your infl will increase more. maybe set the High pressure alert a couple pounds higher.

The extra work I was referring to is the re-inflating. Temp warning is 157°, but if it gets to 115°, I will be pulling over and letting them cool for a while.

[OldCoot]

Originally Posted by Tireman9

sorry Try pg 7

"Never let air out of a hot tire."

Only 2 pages in the link.

[OldCoot]

Originally Posted by Tireman9

..."Never let air out of a hot tire."

While I certainly respect your expertise, I would still like an explanation as to why it is not ok to maintain the Max Cold pressure at all times. Merely stating "Never let air out of a hot tire." is not a reason, but a caution. I suspect that caution is due to the fact that there is a real concern that the tires would not be re-inflated to the proper pressure for the load when they cool. I have never bled a hot tire, but I do and will continue to let them cool if the hot pressure exceeds 10 psi in my particular case more as a safety precaution than anything else.

BTW, hope your surgery is successful and gives the results desired. Good Luck.

[jadatis]

Once contacted a valve importer to ask about the cold and warm pressures.
He wrote me that the temperature inside the tire can rise to boiling point of water ( 100dgrC/200dgr F?) , this by the heat of the breakes transporter trough the rimms to the inside tire filling ( whatever N2 or mixture).
The valves but also the tires can stand that pressure rising.
I estimate the tires to can stand a absolute pressure of 1.5 times the pressure written on the sidewall of C-load and up or belonging to the E-load of yours probably.

But normal inside tire temperature when driving is about 112dgr F/45dgr C.
with that temperature rising from 18dgrC/65dgrF the pressure rises. This asuming the brakes are not used.
With spreadsheet I made ,you can see howmuch, But can be about that 10%.
So if your tires on RV rise more then that , you probably need more cold pressure because the tires loose more energy by to much deflection of the tires, wich is transformed to heat that warm up the tire inside.
At warm outside temperatures the inside will be warmer too, so I think warmed by driving 27 degrC/47dgrF warmer then cold pressure.
So if you for instance use 90 psi instead of 80 psi , it is possible that the pressure rises by the heat lesser so your alarm is not set of at 10%. But then the cold pressure of your TPMS must be set to that 90 psi.

Your tires are probably E-load/10PR with 80psi pressure needed for the maximum load , wich is not the maximum pressure. That discussion is still taking place and Tireman 9 will try to get a meeting with a tire-maker to get it clear, about if that 10psi extra is allowed cold, and totally suported by the TRA .

I once concluded by european information of semperit( from continental) that you are allowed even 1.4 times that 80 psi and Michelin camper tires ( camper is what we call a motorhome) have max pressure of 5.5 bar( 80 psi) written on a 4.8 bar ( 70 psi) D-load tire. So this is 14% higher pressure wich they totally support.
So I am not writing that you should even go to 140% of your 80 psi but that 10 psi is 12.5% of 80 psi.

But first we have to know if your tires need that higher pressure, I expect they will because of the high warm temperature and pressure, or it was after some severe braking. I expect then only rear will rise to much, and front stays OK, but inform me. Front is seldomly overloaded and pressure is kept by most also at 80 psi, wich is mostly not needed ( but there are exeptions), wich would make the pressure- and temperature-rising by only driving less.

I would like to calculate with my spreadsheet for you OldCoot if the rear tires need that 90 psi instead of 80 psi , but need tire date like maximum load and needed pressure for that. and preferably 4 point weighing( or 6 when tandem axle) and build of vehicle like number of axles behind, number of tires on the road . If you dont have the 4-point, weighing , axle weighing , otherwise we have to do with GAWR's.

Could point out that 80 psi is enaugh, so you are mostly doing it for me, I realise. But it could explain the temperature and pressure rising, and if its to much.

If that pressure apears to be to low, damage is done to the tire and stopping to let it cool down dont stop the damage already done. My idea is that if you drive at fi 40 degrees F and it rises to over 87 degrees ( 47 degr more then cold) , you are not alarmed by the temperature and pressure , but still damage is done to the tire by to much deflection. To my opinion the heat is mostly a side effect. and th e to much bending of the sidewall does the most damage.

[Tireman9]

Originally Posted by OldCoot

Only 2 pages in the link.

Strange. I must have copied wrong link. Try this one.

http://www.cruiserlift.com/Literature/RVTIREGUIDE1.pdf

[OldCoot]

Originally Posted by OldCoot

While I certainly respect your expertise, I would still like an explanation as to why it is not ok to maintain the Max Cold pressure at all times. Merely stating "Never let air out of a hot tire." is not a reason, but a caution. I suspect that caution is due to the fact that there is a real concern that the tires would not be re-inflated to the proper pressure for the load when they cool. I have never bled a hot tire, but I do and will continue to let them cool if the hot pressure exceeds 10 psi in my particular case more as a safety precaution than anything else...

Still awaiting an answer.

[Tireman9]

Originally Posted by OldCoot

Still awaiting an answer.

Nuts wrote nice long post and the Internet hiccuped.

When tires are designed and tested they are inflated when at the ambient temperature of the test lab. Then they are loaded and run against a steel drum at various speeds and loads depending on the details of the specific test. Almost all speed and durability tests are run "capped" that means no adjustments to inflation once the test starts. So during the testing the tire heats up and the pressure increases accordingly.
If you were to bleed off the extra air pressure during the test the tires would not run as long as there would be more deflection and of course more heat generated. Since heat is what kills tires on drum tests, we would see more and earlier tire failures.

I don't know why you are so concerned about a 10 psi increase in pressure. I have seen a larger increase many times. The actual pressure increase depends on many factors such as actual load, tire design features such as tread design, rubber thickness and compound selection, cooling air movement around the tire, moisture content of the inflation gas, rim material (steel or aluminum) as well as other factors such as alignment.

If a +10 psi is of major concern I can only suggest you confirm the actual load on each tire and ensure that all tires are inflated to at least 10psi above the minimum needed for the heaviest loaded tire on each axle.
You can decrease the pressure increase by switching to aluminum wheels. You can also lower the pressure rise by using dry inflation gas such as what you would get in an industrial gas cylinder. You can use air, Nitrogen, Argon, Helium or CO2 but I would not use Oxygen or flammable gas for safety reasons.

Hope this helps clear the air.

[OldCoot]

I have alum wheels and a TPMS system and all tires are set at 65# and the pressure gain is within 2# on all tires and only ones that vary are which two tires are on the sunny side of the trailer while traveling. The load does not change. I do not bleed air, but when the pressure monitor sounds @ 10# over cp, I pull over and take a break while they cool. The alum rims are rated to take 65# and no doubt will take more than 75#, but I just don't want to risk it.

[Tireman9]

Originally Posted by OldCoot

I have alum wheels and a TPMS system and all tires are set at 65# and the pressure gain is within 2# on all tires and only ones that vary are which two tires are on the sunny side of the trailer while traveling. The load does not change. I do not bleed air, but when the pressure monitor sounds @ 10# over cp, I pull over and take a break while they cool. The alum rims are rated to take 65# and no doubt will take more than 75#, but I just don't want to risk it.

Can you change the warning level of your TPMS? If not you could establigh the "set" pressure a couple of psi higher or just continue doing what you have been doing.

[OldCoot]

Originally Posted by Tireman9

Can you change the warning level of your TPMS? If not you could establigh the "set" pressure a couple of psi higher or just continue doing what you have been doing.

TST recommends 15%. 0.15X65=9.75 Of course I can set it higher, but will leave it as is and continue stopping when the alarm sounds as we are not in a hurry to get anywhere. Just wanted an explanation which evidently is very elusive. I wasn't concerned with a capped test procedure, just actual practice. BTW, after the 2 times we've stopped for the cooling and the pressure drops to around 69#-70# the alarm never sounds again and the pressure for some reason or other remains around 72#-74#. Weird.

[SBTAR]

The bottom line is that motor homes are usually over weight. You are better to run max cold pressure. Tires run cooler inflated over the pressure needed to carry the load put on them. So if you inflate them to max cold pressure you tire not going to explode because it is going to run cooler,build up less pressure than running them at 65psi,and get better gas mileage.than you won't have to stop to let them cool.