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Old 03-29-2013, 03:24 PM   #43
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I think you guys are talking about apples and oranges.....er, tow vehicle tires and trailer tires. Please pay attention!
Now I have a Dľ.

But I do have Michelins on every wheel I own (except the snow blower and riding mower). I'd better go back to finishing the front steps' railings.

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Old 03-30-2013, 07:46 AM   #44
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I have P type Bridgestones on the Tundra. Max pressure is 44# for 2601 pounds of load carrying capacity. Which puts them in the load range "D" category.
I run the Tundra specs when the truck is empty and not towing. 30 front, 33 rear. Increase to 34 front and 39-40 rear.

Ok. It might be time for my lecture on Load Indicators.

Passenger Car tires come in Standard Load (SL) and Extra Load (XL).

Light Truck tires, Truck tires, and many other types come in Load Ranges (eg LR C).

There are some types of tires that come in Ply Ratings ( eg. 24 PR)

All tires used to come in PR's but since it was common for people to confuse "Ply Rating" with the actual number of plies, they went to different systems to eliminate the confusion. - BUT - many people still refer to the old system by saying (incorrectly, I might add), "I have 10 ply tires" - when the correct term is "I have Load Range E tires.".

In the case of passenger car tires, the pressure listed on the sidewall might be indicated as "Max Load XXXX at YY psi"

- and for Standard Load tires, YY would equal either 36 psi (for tires done in the metric system) or 35 psi (for tires done in the English system)

- and for Extra Load Passenger Car tires, YY would equal 41 psi for both metric and English.

- BUT - the sidewall might also say "Max Load XXXX, Max pressure YY

- and for Standard Load tires YY = 35, 36, 44, or 51 psi.

- and for Extra Load tires YY = 41, or 50 psi.

- AND -

It is not uncommon for there to be "mistakes", "errors", "differences in interpretations", etc., when it comes what pressure is displayed on the sidewall on passenger car tires. You will see some tires with versions of the above, and I think they are incorrectly labeled.

For Light Truck tires, it's a little more consistent. Load Range C tires will have 50 psi on the sidewall, 65 psi for Load Range D, 80 psi for Load Range E, etc. (with some exceptions, which I won't go into)

Truck tires, follow a similar pattern: Load Range F = 95 psi, Load Range G = 110 psi, etc - and again there are some exceptions, which I won't go into.

It's important to be aware that the system for Passenger Car tires is different than for Light Truck, and Truck tires.

And lastly, ST type tires and other trailer type tires follow the "Load Range" system, similar to LT tires.
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Old 03-30-2013, 09:05 AM   #45
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So are you saying my interpretation of the load rating of 2601 pounds at 44 psi is what I should use when calculating the weight carry capacity of the tire?
My thought is that these tires should not be inflated beyond 44 psi. And since I am no where close to the 5202 pound rating for the 2 rear tires. There is no need to put the full 44 psi in the rear tires.
Has anyone considered the rating of the rim, when they go from a "C" rating tire to a "D" or "E" rating?
I would bet money that OEM rims on a TV are in the same load range as the tires that came on it from the factory.
By increasing the pressure to 80 psi. Wouldn't you run the risk of damage to the rim?
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Old 03-30-2013, 11:48 AM   #46
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Capri, thanks for more info. I have gotten so mixed up lately, I should hide under the table for a while, but I press forward.

I have seen another rating system in the past few years. I assumed it was going to eventually replace the load range system. Most of the LT tires I looked at were, very roughly, rated 110 and up. This would be a better system as it accounts for more variations in tires, but I wish we had one system and stuck with it.

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Old 03-31-2013, 06:22 AM   #47
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Originally Posted by TG Twinkie View Post
So are you saying my interpretation of the load rating of 2601 pounds at 44 psi is what I should use when calculating the weight carry capacity of the tire?
My thought is that these tires should not be inflated beyond 44 psi. And since I am no where close to the 5202 pound rating for the 2 rear tires. There is no need to put the full 44 psi in the rear tires.
Has anyone considered the rating of the rim, when they go from a "C" rating tire to a "D" or "E" rating?
I would bet money that OEM rims on a TV are in the same load range as the tires that came on it from the factory.
By increasing the pressure to 80 psi. Wouldn't you run the risk of damage to the rim?

First, what I am saying is those tires are not Load Range D tires. They are Standard Load P type tires.

Second, it would be wrong to say the max load on those tire occurs at 44 psi (even if it says that!) The max load on those types of tires occurs at 35 psi (or 36 psi if the are metric)

And, Yes!, you shouldn't exceed 44 psi cold for those tires.

What pressure to use in your truck? What does the vehicle tire placard say? (If the tire size is the same as what is written there, then the pressure is appropriate as well.) And why weren't you discussing the front tires?

Rims? It is my understanding that most rims are pretty generic and are designed to be used for the worst case. And just so we are clear, if the load on the rim stays the same, the Load Range of the tire mounted on it makes no difference.

And lastly: I have always wondered why wheels and rims do not routinely carry a max pressure like tires do. The fact that they don't leads me to believe that pressure is just not that important.

In the quest for information on the subject, I have encountered only 2 people who I thought qualified to answer the question, and they both said it is the load that is way, way more important. The stress added by inflation pressure is relatively minor - and for practical purposes can be ignored - unless you are making HUGE changes. A change from 50 psi to 80 psi would not be significant - compared to the load on the wheel.
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Old 03-31-2013, 06:30 AM   #48
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Capri, thanks for more info. I have gotten so mixed up lately, I should hide under the table for a while, but I press forward.

I have seen another rating system in the past few years. I assumed it was going to eventually replace the load range system. Most of the LT tires I looked at were, very roughly, rated 110 and up. This would be a better system as it accounts for more variations in tires, but I wish we had one system and stuck with it.

Gene
That is "Load Index". It's another way of saying "Max Load". It is NOT a replacement for "Load Range".

For example a P195/65R15 SL has a Load Index of 84, while a P225/75R15 SL has a Load Index of 102.

An LT235/75R15 Load Range C has a Load Index of 104/101 (Single/Dual), while a Load Range E in the same size has a Load Index of 116/113.

I know, I know. It's a little complex. But it's been that way for quite some time and there isn't an easy way to do this.
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Old 03-31-2013, 07:39 AM   #49
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Actually, and "XL" on the tire means, Extra Load, and usually at an inflation pressure of 44psi, and normally these tires are found on SUVs and pickups. From Wickipedia:

LL: Light Load; tires for light usage and loads
SL: Standard Load; tire for normal usage and loads
XL: eXtra Load; a tire that allows a higher inflation pressure than a Standard Load tire, which increases the tire's maximum load

All the info is here: Tire code - Wikipedia, the free encyclopedia
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Old 03-31-2013, 09:55 AM   #50
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The tires are P275/65R18 114T M+S Max load 2601 @ 44psi
What pressure to use in your truck?When the truck is empty and not towing I run 30psi in the front and 33psi in the rear.
What does the vehicle tire placard say? (If the tire size is the same as what is written there, then the pressure is appropriate as well.)Door placard is 30psi front; 33psi rear. Tires are the same as the placard.
And why weren't you discussing the front tires? The rear axle is where the load is, not considering the WD hitch. When the box is loaded (not towing) you can't use a WD hitch. When towing, I run 33psi front and 40psi rear.
The front axle rating is 3900#. The rear is 4100#. GVWR is 6900#.

The 114T number is higher than the 104T mentioned above on these tires.
An LT235/75R15 Load Range C has a Load Index of 104/101 (Single/Dual), while a Load Range E in the same size has a Load Index of 116/113.
First, what I am saying is those tires are not Load Range D tires. They are Standard Load P type tires
My tires fall in between the 104 for "C" range and 116 for "E" range. So they are in the "D" range. So I guess they are not "P" rated metric.
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Old 03-31-2013, 10:06 AM   #51
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Originally Posted by TG Twinkie View Post
The tires are P275/65R18 114T M+S Max load 2601 @ 44psi
My tires fall in between the 104 for "C" range and 116 for "E" range. So they are in the "D" range. So I guess they are not "P" rated metric.
From the data charts on the Wikipedia site, your tires are rated for (104) 2000 pounds each, and a max speed rating of (T) 118 MPH.

It appears the manufacturers are getting away from the old C,D, and E, etc., ratings, just like in the past they got away from the 4,6, and 8 ply ratings.
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Old 03-31-2013, 10:09 AM   #52
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When using the XL style tire on a trailer, the sidewall information must be "derated" 10% per:

49 CFR 571.110
Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10,000 pounds) or less.

S4.2.2.1
Except as provided in S4.2.2.2, the sum of the maximum load ratings of the tires fitted to an axle shall not be less than the GAWR of the axle system as specified on the vehicle's certification label required by 49 CFR part 567. If the certification label shows more than one GAWR for the axle system, the sum shall be not less than the GAWR corresponding to the size designation of the tires fitted to the axle.

S4.2.2.2
When passenger car tires are installed on an MPV, truck, bus, or trailer, each tire's load rating is reduced by dividing it by 1.10 before determining, under S4.2.2.1, the sum of the maximum load ratings of the tires fitted to an axle.

S4.2.2.3
(a) For vehicles, except trailers with no designated seating positions, equipped with passenger car tires, the vehicle normal load on the tire shall be no greater than 94 percent of the derated load rating at the vehicle manufacturer's recommended cold inflation pressure for that tire.
(b) For vehicles, except trailers with no designated seating positions, equipped with LT tires, the vehicle normal load on the tire shall be no greater than 94 percent of the load rating at the vehicle manufacturer's recommended cold inflation pressure for that tire.

Thus the Michelin LTX (P) 235/75R15 XL sidewall data of 2,183 pounds @ 50 psi is derated to 1,985 pounds on a trailer when considering load capacity.

Per the factory literature and trailer data plate, an International model 25FB has a GVW of 7,300 pounds. My unit has a tongue weight of 1,200 pounds per Sherline scales. With the Hensley hitch, the theory is that the trailer carries 1/3 of the tongue weight. The trailer axles are carrying (7,300 - 800) 6,500 pounds. The four derated load capacities total 7,940 pounds so there is a 22% safety factor on loading.

My experience with the GYM OEM tires was a 10% air pressure drop in five weeks of storage. The Michelins lost perhaps 1 pound in seven weeks of storage using the same tire pressure gage.

YMMV
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Old 03-31-2013, 10:12 AM   #53
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I don't get it! The data I posted is right from the tire sidewall. Not Wikipedia.
Max load at 44psi is 2601#.
The 114T means what? The max speed? Who drives at 114 mph?
Are the tires "P" rated or not? One would assume the "P" in P275 means they are.
Even when derated to 90% they still exceed the load carrying capacity of the TV. 2601x .90= 2341# per tire. 4 tires = 9364#. 135% of the TV capacity.
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Old 03-31-2013, 10:17 AM   #54
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I don't get it! The data I posted is right from the tire sidewall. Not Wikipedia.
Max load at 44psi is 2601#.
The 114T means what? The max speed? Who drives at 114 mph?
I'm just quoting the data from the chart on Wiki, and sorry I made a mistake the 114, not 104, means 2600 lbs, and the T means 118 MPH.

Doesn't mean you HAVE TO drive 118, means the tires can handle 118 mph.
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Old 03-31-2013, 11:56 AM   #55
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Thanks again Capri for telling me there is a difference between LR and Load Index, though I'm not sure my mind is stretching enough to quite get traction on it.

Yes, this gets complicated and I start making rubber jokes (every boy should have some in his wallet). As a further diversion, there's a movie called Rubber. It is about a sentient tire that travels around the desert. When it rolls up to someone and he mocks the tire, it starts shaking and then kills him. There's more to it than that, but that's enough for now. It sometimes is on the Movie Channel in the middle of the night. Remember, be careful what you say to a tire, just in case.

As travel season gets closer, tire threads get more active. I don't know if I can take another summer of tire threads.

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Old 03-31-2013, 01:35 PM   #56
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Thanks again Capri for telling me there is a difference between LR and Load Index, though I'm not sure my mind is stretching enough to quite get traction on it.

Yes, this gets complicated and I start making rubber jokes (every boy should have some in his wallet). As a further diversion, there's a movie called Rubber. It is about a sentient tire that travels around the desert. When it rolls up to someone and he mocks the tire, it starts shaking and then kills him. There's more to it than that, but that's enough for now. It sometimes is on the Movie Channel in the middle of the night. Remember, be careful what you say to a tire, just in case.

As travel season gets closer, tire threads get more active. I don't know if I can take another summer of tire threads.

Gene
Just watch out if you meet a random tire in the desert, i suppose. ...and certainly don't question his load rating! Haha!
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