Tire Pressure

[Ford Idaho]

Tires are built to handle the increased pressure when the air inside is heated, how well they handle that increase is anyone's guess.
All it takes is one unseen blemish.

[BarryD0706]

Originally Posted by OldCoot

And the source of that objective evidence you are quoting?

Tireman9's blog. Specifically paragraph 6: http://www.rvtiresafety.com/2013/06/...ssure.html?m=1

[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.

[OldCoot]

Originally Posted by BarryD0706

Tireman9's blog. Specifically paragraph 6: RV Tire Safety: Had a question about High Pressure

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.

[ependydad]

I actually did see something about not letting air out of hot tires somewhere recently... I need to recall where, though.

[acadianbob]

All rated tire temperatures are "cold". Of course the pressure goes up once you get rolling. The manufacturers are not stupid and the product is designed to handle this increase in pressure. There is no need to ever let air out of tires because they have warmed up.

Can a tire blow because of too much pressure? Sure. But the reasons are going to be overloading and/or over the speed rating for the tire.

[BarryD0706]

OC, the example you give is the case where a large change is ambient temperature has increased the "cold pressure" to the wrong value. I've been thru that once, and yes, I readjusted the pressure (with them hot) also.

For Taylorgso's case, let's use my RV which requires that my tires be at 80psi (cold) to carry the load. The "Max Pressure" on the sidewalls is also 80 pounds. Because Taylorgso has this totally wrong idea that the "Max Pressure" rating is a hot pressure, and based on what he said, he will put ~72# of cold pressure into my tires so that they don't exceed the "Max Pressure" when they get hot.

Because of this incorrect thinking, which you seem to want to say is ok, my tires will be severely under-inflated and blowouts are likely to follow. Then Taylorgso will be back here talking about the "junk" Maxxis tires when in fact the problem is "user error".

[TURBS]

Originally Posted by BarryD0706

But I've always heard never to let air out of a hot tire because you think it's over-pressure.

I'd believe this statement.

[OldCoot]

Originally Posted by BarryD0706

OC, the example you give is the case where a large change is ambient temperature has increased the "cold pressure" to the wrong value. I've been thru that once, and yes, I readjusted the pressure (with them hot) also.

For Taylorgso's case, let's use my RV which requires that my tires be at 80psi (cold) to carry the load. The "Max Pressure" on the sidewalls is also 80 pounds. Because Taylorgso has this totally wrong idea that the "Max Pressure" rating is a hot pressure, and based on what he said, he will put ~72# of cold pressure into my tires so that they don't exceed the "Max Pressure" when they get hot.

Because of this incorrect thinking, which you seem to want to say is ok, my tires will be severely under-inflated and blowouts are likely to follow. Then Taylorgso will be back here talking about the "junk" Maxxis tires when in fact the problem is "user error".

You are wrong! Taylorgso states that he starts his trip with 65 cold and limits it to 80 hot. Nowhere does he state that he starts underinflated and I never stated doing it either.
I'm out of here.

[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.

[OldCoot]

Mikegjax, the tire placard on the trailer is useless if the tires have been upgraded to a higher load range. Same goes for the truck placard. Tire pressure will increase more than 5# or 6# in a very short time on the road. I have experienced pressure increases of 10#, which sounds the TST TPMS alarm. Did I bleed them off? No, we just took a coffee/pie break and let them cool off for about 30-45 min. Had we been in a hurry and not wanted to take the break, I would have bled them off and re-inflated the next morning. The temperature alarm is factory set at 157° as TST states that most tire failures occur between 180° & 200°.

[PhoneDude 8289]

Would inflating with nitrogen make a difference cold vs hot tires.

[OldCoot]

Originally Posted by presley01

Would inflating with nitrogen make a difference cold vs hot tires.

Have heard that the tires run cooler, but have no experience with the Nitrogen filled tires. Normal air is approx. 78% Nitrogen. Don't know if the additional 22% would help.

[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.

[Tireman9]

Originally Posted by patmcwhirter

I am a new owner of a 24S and I can see that suspension upgrades are needed right out of the box. I have ordered the Hellwig sway bar and will make a decision on shocks after I install it. Because of this I have come to the conclusion that the sprinter chassis was designed for a lighter cargo van and is maxed out with the motorhome weight. So I am now pondering tire pressure and wondering if it should be increased also. I would appreciate any thoughts you have on this, and would like to know if anyone agrees and has increased tire pressure, and what were your results in handling and increased MPG.

It would help if you could provide some numbers. Your placard will have data for GAWR and GVW. You should also have a label showing the capacity of additional load for your vehicle.
Tire size and Load Range will help us provide answers on the tires and your actual load as measured on a certified scale will help confirm some important numbers.

[Tireman9]

Originally Posted by OldCoot

As long as he re-inflates them to the right pressure when cold, it shouldn't hurt a thing. Just more work.

Absolutely NOT. You should never let air out of your hot tire. Doing so and then reinflating that evening is NOT a good idea. Also a lot of un-necessary work. Tires will normally run 10 to 25 psi above the cold infla depending on a number of variables.

[Tireman9]

Originally Posted by BarryD0706

I guess we'll just agree to disagree. Perhaps Tireman9 can educate one of us.

Tires are designed and tested at a "caped" air pressure. That means the infl is set when the tire is at ambient and not adjusted during the durability or high speed regulatory tests. Tires will get hot and the pressure will increase. This is what is supposed to happen.
If you lower the inflation (when hot) the tire will flex more so it will generate more internal heat and more internal structural damage will occur. This will cut tire life considerably. You will not find a tire engineer ever suggesting bleeding hot air for regular road service.

[OldCoot]

Originally Posted by Tireman9

Absolutely NOT. You should never let air out of your hot tire. Doing so and then reinflating that evening is NOT a good idea. Also a lot of un-necessary work. Tires will normally run 10 to 25 psi above the cold infla depending on a number of variables.

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#.

[Tireman9]

Originally Posted by OldCoot

Just means that you need to add air when the tire cools. Makes no sense to me to deflate a hot tire, but if that's what the man does, it can't do any harm as long as he re-inflates when the tires cool. Will say this, over inflating hot tires will definitely stretch them. We used to over inflate tires on our race car and set them in the sun to stretch them. We could get the circumference to change by as much as 3"-4" over stock, which is how we got "tire stagger".

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.

[Tireman9]

Originally Posted by Taylorgso

So you're saying if I set preferred cold pressure and pressure builds to 85psi on a hot day (exceeding stated sidewall pressure) I should run them at that pressure? I disagree... But to each his own. I've blown tires in the past running them at excessive pressure when hot.

If you have "blown" tires that means they were probably run low flex failures.

Tires are designed to handle three to five times the pressure on the sidewall. If you read the words you will see the cold pressure does not say "max pressure" but "Max Load @ xyz pressure"