Haul it or trailer it

[JR]

One gains about 1psi per 10deg F increase. As long as the tire isn't getting stressed by something, it shouldn't gain much temp. Humans can always screw things up tho. If you set tire pressures at dawn in the high desert in Summer it can be 50deg. Then you lose some altitude and it's 110deg with direct sunlight adding 20 more deg. As with all things, a person has to use some common sense.

Yes thats true for a tire that is stationary and not moving. Thats not taking into account the heat that the tire will generate. GoodYear says tire pressures can increase by as much as 10-20% when the tire is loaded to 75% of it's rating.

 

[RustyJC]

Thats not taking into account the heat that the tire will generate. GoodYear says tire pressures can increase by as much as 10-20% when the tire is loaded to 75% of it's rating.

I can vouch for that. I run a TST 507 tire pressure/temperature monitoring system on the truck and 5th wheel. The Goodyear G114 tires (215/75R-17.5 rated 4805 lbs @ 120 PSIG) on the RV will increase in pressure from 120 PSIG cold to 137 PSIG after 4 or so hours on the interstate at 65 MPH with temperatures still well in hand. The increase in pressure in the truck tires is significantly less.

As an aside, I'm going to have to go back into the monitor and reset the high pressure alarm on the trailer tires. I had arbitrarily set it at 140 PSIG when I recently installed the system. The actual readings from the first trip out with it suggest that I may want to bump that to 145-150 PSIG or so, especially since the ambient temps were only in the 80s during the first trip.

Rusty

 

[AH64ID]

I have noticed that the temperature of my LRG 19.5" tires gets hotter than the LRE 17's did, even thou the LRG's are at a lower %age of weight capacity and have more air than required by the Toyo chart.

It must be the design of the HD tires that holds more heat, and I also think they use a lower volume of air since the sidewalls are much thicker.

 

[RangerGress]

Post deleted. Didn't read previous post correctly.

 

[AH64ID]

He said 10-20% pressure increase, not temperature increase.

44psi + 20% is 53 psi.

Personally I wouldn't run above sidewall pressure unless you are starting at 6K feet and quickly dropping to sea level and staying there.

 

[RangerGress]

He said 10-20% pressure increase, not temperature increase.

44psi + 20% is 53 psi.

Personally I wouldn't run above sidewall pressure unless you are starting at 6K feet and quickly dropping to sea level and staying there.

Yes, I misread his post, my fault.

IMO putting some extra pressure into a low psi tire is pretty common. Personally I do it all the time. The OEM 20" tires say, what 36psi or so? I run mine at 45psi when I'm towing. They've not indicated more then a couple psi of pressure growth. I think the 20% pressure growth figure is extreme. We're not racing these things, sliding thru turns and braking at threshold. We're just driving down the freeway. In the example above 9psi of pressure growth means 90deg F of temp change. When I finish a road trip my tires are only slightly warmer then at trip start. And consider this.....more air in the tire means less stress on the sidewall. That could mean less temperature increase. So maybe a 35psi tire would experience 6psi pressure growth whereas a 45psi tire experiences 2-3psi of growth.

 

[JR]

Yes, I misread pressur, my fault.

IMO putting some extra pressure into a low psi tire is pretty common. Personally I do it all the time. The OEM 20" tires say, what 36psi or so? I run mine at 45psi when I'm towing. They've not indicated more then a couple psi of pressure growth. I think the 20% pressure growth figure is extreme. We're not racing these things, sliding thru turns and braking at threshold. We're just driving down the freeway. In the example above 9psi of pressure growth means 90deg F of temp change. When I finish a road trip my tires are only slightly warmer then at trip start. And consider this.....more air in the tire means less stress on the sidewall. That could mean less temperature increase. So maybe a 35psi tire would experience 6psi pressure growth whereas a 45psi tire experiences 2-3psi of growth.

Your last statement makes sense, less air pressure in a tire = more rolling resistance compared to a tire with higher pressure (assuming the same load.) Also In the same study released by GoodYear I also noticed the higher the capacity the tire the more the pressures increased. This was all assuming 75% of that particular tires rating.

 

[RustyJC]

Also in the same study released by GoodYear I also noticed the higher the capacity the tire the more the pressures increased.

Is this study in the public domain? If so, if you could provide a link to it, I would greatly appreciate it. With the results I cited above (post #22), I'd like to see Goodyear's analysis of what's going on. Since I didn't see a temperature increase commensurate with the pressure increase, something's happening here that doesn't follow the Ideal Gas law.

Rusty

 

[AH64ID]

The OEM 20" tires say, what 36psi or so? I run mine at 45psi when I'm towing.

I do believe they are 44psi rated, so 45 is only 1 psi high

2601lbs @ 44psi, giving a RAWR of 5202lbs in tires.

A quick look at the Ram towing guide shows all 2014 1500's have a RAWR of 3900lbs. So 100% of the RAWR puts the tires at 75%.

Stick with sidewall pressures.

 

[JR]

Is this study in the public domain? If so, if you could provide a link to it, I would greatly appreciate it. With the results I cited above (post #22), I'd like to see Goodyear's analysis of what's going on. Since I didn't see a temperature increase commensurate with the pressure increase, something's happening here that doesn't follow the Ideal Gas law.

Rusty

It certainly is, I happened across it 6 Months or so ago when I was researching new tires for the wife's SUV. They had several links at the bottom of the page on Tire Rack's website that caught my eye pertaining to everything from proper rotation, inflation, effects of pressure from temperature and elevation, and so forth. It was in one of those links they had GoodYear's report. I didn't save it but I will go back through Tire Rack's website when I get home and see if I can find it.
Maybe my wording was confusing or misguided, but everything they said seems to go along with what you reported in your above post. You saw a higher margin of increase in pressures on your LRG tires than you did on your LRE tires.

 

[RangerGress]

I do believe they are 44psi rated, so 45 is only 1 psi high

2601lbs @ 44psi, giving a RAWR of 5202lbs in tires.

A quick look at the Ram towing guide shows all 2014 1500's have a RAWR of 3900lbs. So 100% of the RAWR puts the tires at 75%.

Stick with sidewall pressures.

Then I must be running them at 49-50psi when I tow. Thanks for fixing my #'s. It was the 5psi over that I'd focused on, not the base pressure.

Re. stick with the sidewall pressures. We'll have to agree to disagree. Passenger tires have weak sidewalls. Giving them a little extra support is reasonable, and a common practice. It reduces sidewall stress which means cooler, more survivable tires.

 

[AH64ID]

Then I must be running them at 49-50psi when I tow. Thanks for fixing my #'s. It was the 5psi over that I'd focused on, not the base pressure.

Re. stick with the sidewall pressures. We'll have to agree to disagree. Passenger tires have weak sidewalls. Giving them a little extra support is reasonable, and a common practice. It reduces sidewall stress which means cooler, more survivable tires.

I have to say your the first person I have ever heard recommend above sidewall pressures on P tires, so in my world it seems anything but common. The MDT and HDT tires that have additional pressure charts, above sidewall, also have much lower speed limits for those pressure/weight ratings.

Why would you want to put more outward stress on weak sidewalls? You are over-stressing the sidewalls, just it a different manner. It's not how they where designed to work.

Like I mentioned, at the trucks RAWR you are only loading the tires to 75% so there is zero need for additional pressure.

So far I see a trend with your posts.. Run sidewall pressures above limits and tow above limits. Sounds like you should have stuck with the 3/4 ton truck

 

[cerberusiam]

Passenger tires have weak sidewalls. Giving them a little extra support is reasonable, and a common practice. It reduces sidewall stress which means cooler, more survivable tires.

ATTENTION: DO NOT TRY THIS AT HOME!!!!!!!

The only thing remotely "common" about this practice is how uncommonly STUPID it is!!! :--) The only people I see believing this are the same ones that believed the salesman that told then they can pull that 9k travel trailer with a Nissan Pathfinder with no issue.

Adding more air adds MORE stress to an already weak sidewall that is already over stressed if one is considering adding air. The end result will be a catastrophic failure at an inopportune time. There is NO fix for an over loaded tire EXCEPT a heavier tire. Period!

 

[RangerGress]

Altho I'm a mechanical engineer, I don't know more about tires than any other consumer. My perception tho is that the idea is that a bit more air pressure means reduced sidewall stress. If you look at a heavily loaded tire you can see the how the sidewall flexes significantly near the tire's contact patch. It's easy for me to imagine that significant flexing there would cause a temp increase and weaken the tire due to the flexing and straining of the belts.

The design and strength of woven structures like cables and woven fabrics is it's own specialty, and another area that I don't know spit about. But the basic idea is that it can tolerate a bit of flexing w/o losing it's strength and durability characteristics. But if it's pushed a little too far, then the stress goes beyond the elastic range into genuine strain and microdamage occurs. Once that starts occurring the damage accumulates and the structure becomes steadily weaker.

I learned this idea from the trailer guys. It's entirely possible that they don't know what they are talking about and a couple extra psi is a bad idea. The trailer guys did not explain the science behind their wisdom. If the science isn't explained adequately, one should be skeptical.

 

[AH64ID]

There are some ST tires that have service bulletins authorizing an additional 10 psi over sidewall pressure, this doesn't exist on P or LT tires that I have ever seen.

At the RAWR you are only operating your tires at 75% of their rated weight, 44 psi is "overinflated" for the weight and more than adequate.

 

[cerberusiam]

The sidewalls are made to flex to maintain the contact patch and provide the ride quality, not neccessarily the load capability. Pressure is not only vertical from the gound contact it is outward on a lot more surface area than vertical. Stretching the sidewall with more pressure just hastens its demise by overloading its ability to maintain its shape. Rated tire pressures are more about sidewall ratings than tread ratings on any tire. If the tire needs more than rated pressure to reduce the bulging at ground contact it is overloaded anyway.

 

[Top]

Interesting tire argument. I would ask Barry. He is a tire engineer.
http://www.barrystiretech.com/
Lots of good reading on his site.