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Old 03-23-2015, 10:11 AM   #15
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[QUOTE=nickcrowhurst;1597386]
Quote:
Originally Posted by Tireman9 View Post
Couple of comments.
The tables are fro Tire & rim Association yearbook not Rubber Manufacturers Association but this is minor point.
QUOTE]

You will note that I carefully said that "The RMA chart is reproduced here:"
I have the original RMA table, and it is identical to the earlier one from the Tire and Rim Association to which I linked.

At the top of each chart, including the one I use, table LT-1R (single) for radial tires, is the statement:

"The following chart has basic load information for various tire air pressures and vehicle speeds for radial ply tires. Always consult the tire manufacturer's specific information for the tire you have fitted for confirmation of these values."

Nick.
Nick you got it correct. I didn't read the fine print and I knew the RMA doesn't publish the Load Inflation tables only TRA does and yes someimes others do "reproduce" the TRA tables.

My main concern was that some might not pay attention to the size issues.
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Old 03-24-2015, 06:56 AM   #16
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To answer the OP's question:

First we need to know what the vehicle tire placard says for both tire size and inflation pressure. That information will tell us what the vehicle manufacturer specified for load carrying capacity.

Then, we match that with the new tire size using the load tables.

I've said it before, but it is worth repeating:

The load tables are MINIMUMS, not recommendations. DO NOT run your tires according to that table. Use more!! The above procedure will insure you are doing EXACTLY that - unless, of course, you are overloading your vehicle and in that case all bets are off!
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Old 03-24-2015, 07:16 AM   #17
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I look at max on the tire. Mine are similar to yours except 20" LT Michelins. I can never remember 80 rear 70 front so I run 75 all around, all the time. I also have Michelin LT 16' on the AS and run 72 all around in those.

Ride is a little rough when not towing, but great when towing. Dealer says to run 45 on the F350, but then dealers notoriously know nothing about tires, even the service department. A friend owns a tire dealership and has most brands and he recommends 80 on the TV all around and 75 on the AS. So I am close to what he recommends.
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Old 03-24-2015, 09:13 AM   #18
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I still have the original equipment tires so I go with the door placard, which is 33 psi for my truck and 20" P-rated tires. I replaced the tires at 35,000 miles. They still had plenty of tread, but were dry rotted. I got original equipment the second time around because I got a set of 4 tires for $500. Maybe I'll do something different next time. Starting my 6th season towing this way with no ill effects.
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Old 03-24-2015, 10:56 AM   #19
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I still have the original equipment tires so I go with the door placard, which is 33 psi for my truck and 20" P-rated tires. I replaced the tires at 35,000 miles. They still had plenty of tread, but were dry rotted. I got original equipment the second time around because I got a set of 4 tires for $500. Maybe I'll do something different next time. Starting my 6th season towing this way with no ill effects.

With P-type tires the max load number that is on the tire needs to be de-rated by dividing by 1.1. Then knowing that number you should get the TV & TT on a truck scale so you can confirm you are not overloading any of the tires.
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Old 03-24-2015, 01:42 PM   #20
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I don't get "de-rating". If the number isn't the number, why is it there?
I will just keep doing what I've been doing until I feel what I'm doing might cause death, injury, or property damage. So far I haven't felt like that.


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Old 03-24-2015, 02:07 PM   #21
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I don't get "de-rating". If the number isn't the number, why is it there?
DOT 49 CFR Part 571 Docket No. NHTSA-03-15400 RIN 2127-AI54

From the first paragraph on that page:
"RMA and GRRF supported NHTSA's retention of the 1.10 load service factor used to reduce the load rating of passenger car tires when installed on an MPV, truck, bus, or trailer, as specified in Part 571.110 Paragraph S4.2.2.2 of the proposed rule. RMA believed that this reduction in load rating is necessary for the reasons stated by NHTSA and is also appropriate to reduce the load rating for passenger car tires used on light trucks, vans, SUVs, and trailers for the following reasons: 1) higher stress on the tire due to the higher center of gravity of these vehicles; 2) more severe service conditions as compared to passenger cars; 3) greater potential for overload due to open cargo areas and increased likelihood for towing; and 4) more tire related problems on light trucks, SUVs, and vans."

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Old 03-24-2015, 08:51 PM   #22
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Let's see if I am interpreting this correctly-
Basically the sidewalls are stiffer/stronger on LT tires versus passenger tires?
Maybe I will get truck tires next time, but they are not available in my specific size. Maybe I can go 10 mm larger and get some truck tires?


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Old 03-25-2015, 02:20 AM   #23
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Let's see if I am interpreting this correctly-
Basically the sidewalls are stiffer/stronger on LT tires versus passenger tires
A detailed explanation is here:http://www.tirerack.com/tires/tirete....jsp?techid=70

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Old 03-25-2015, 05:50 AM   #24
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Originally Posted by m.hony View Post
I don't get "de-rating". If the number isn't the number, why is it there?
I will just keep doing what I've been doing until I feel what I'm doing might cause death, injury, or property damage. So far I haven't felt like that.


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I think where people get confused about the derating of passenger car tires for use on light trucks and trailers is that - first - there is a difference in the service conditions, and that affects the load carrying capacity of a tire. In other words, it isn't a simple, straight forward thing - it's confounded with a bunch of things.

The load carrying capacity of a tire is affected by a great many things - size (physical dimensions), inflation pressure, speed, road surface roughness, suspensions stiffness, etc. So the load carrying capacity depends on what those conditions are.

So when a tire load table is developed, it has associated with it those characteristics that are part of that type of service. So a P type tire is designed to go on a passenger car - high speed, smooth road, soft suspension - and the tables reflect that. A separate load table COULD have been published that delineates what the load would be for light truck service - slower speeds, not as smooth roads, stiff suspension, etc. That same tire COULD be used in off road conditions, and another table could have been developed for those conditions.

BUT, rather than do that, they applied a simple rule: When a P type tire is used in an LT application, its load carrying capacity is reduced 10% to reflect the different operating conditions. The load table for an LT tire already has compensated for those factors.
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Old 06-22-2015, 01:07 PM   #25
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Hope that I am not breaking into this thread but I need some help with tire pressure settings and factory t.p.m.s. On my new pickup.
The truck is a 2015 gmc Sierra , Max tow 1500. When it arrived at the dealership it had a set of Goodyear "p" rated tires which I did not want. I had the dealer swap them out for a set if Michelin LTX 10 ply e rated tires. I like to run these at 55 to 60 psi as it gives me a good ride and a stiffer tire. The problem is with my factory TPMS alert system. If I put more than 45 psi the warning system goes off. I don't want any warning lights lit up on my dash as I go along. So"..........
1. My dealer says that they cannot over ride the max setting! Can this be reset or reprogrammed?
2. Do I just have too much tire on my truck?
3. Do I just live with the light coming on?
4. Will I do harm to my tires if I run them below the max rated pressure?

As usual I appreciate any assistance provided.
P.s. I am running 20 " factory chrome rims. I do not know the max allowable operating pressure for the rim configuration. I may be able to get it from my dealer.( or not!)
Thanks
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Old 06-22-2015, 10:28 PM   #26
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Hope that I am not breaking into this thread but I need some help with tire pressure settings and factory t.p.m.s. On my new pickup.
The truck is a 2015 gmc Sierra , Max tow 1500. When it arrived at the dealership it had a set of Goodyear "p" rated tires which I did not want. I had the dealer swap them out for a set if Michelin LTX 10 ply e rated tires. I like to run these at 55 to 60 psi as it gives me a good ride and a stiffer tire. The problem is with my factory TPMS alert system. If I put more than 45 psi the warning system goes off. I don't want any warning lights lit up on my dash as I go along. So"..........
1. My dealer says that they cannot over ride the max setting! Can this be reset or reprogrammed? I believe this is true as the computer programing for vehicles is not in a number of separate components but in the main computer.
2. Do I just have too much tire on my truck? Are the LTX tires the same size as the OE P tires except for the LTX MS/2 being LT type vs the OE P type or are there dimension changes too. Giving tire size would help us answer rather than guess. You got the MS/2 not just the MS? Again more complete id of the tires you are talking about would help.
3. Do I just live with the light coming on? Maybe. I bet that even if you set the tires to 40 psi cold you would get a warning when they warmed up.
4. Will I do harm to my tires if I run them below the max rated pressure? No but you would do harm if you run less pressure than what is specified for the measured actual load on the tires. Have you been on a scale when fully loaded and the TT is hitched on?

As usual I appreciate any assistance provided.
P.s. I am running 20 " factory chrome rims. I do not know the max allowable operating pressure for the rim configuration. Maybe not much higher than the max pressure on the OE P type tires (45 to 51 I think) I may be able to get it from my dealer.( or not!) You got LT275/65R20/E 126/123R LT Michelin LTX Load Range E tires ? That's a LOT more tire than I suspect you needed. Here I am guessing.
Thanks
Pete

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