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Old 11-17-2014, 11:13 PM   #15
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When figuring hitch weight for trailers people with passenger (P) tires often forget to derate them. P tires must be derated for service on pick-up trucks. The vehicle manufacturer automatically does that for proper fitments. However, it’s not mentioned in the owner’s manuals or on the certification labels. So, your tires rated at 2405# are actually rated at 2004# for service on your truck.


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Old 11-19-2014, 09:47 AM   #16
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Good to know - so my tires are rated for 2205 lbs as a p-metric tire - but in light truck applications they are rated for 2005 lbs. I'm still good as far as GVWR as the truck is rated for 7200 lbs (assuming relatively even distribution of weight on four tires with a weight distribution hitch).

Thanks for the info.
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Old 11-19-2014, 10:35 AM   #17
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Your posted max load (printed on tire sidewal)l is achieved only at max pressure printed on sidewall also.
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Old 11-20-2014, 06:19 AM   #18
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Originally Posted by Moflash View Post
Your posted max load (printed on tire sidewal)l is achieved only at max pressure printed on sidewall also.
Not quite. Sometimes the max load and the max pressure are listed as separate items. Further, the maximum allowable pressure is NOT the pressure where the load carrying capacity maxes out.

But sometimes, the pressure where the load carrying capacity maxes out IS listed on the sidewall.

It's confusing and inconsistent, but that is the way it is.
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Old 11-20-2014, 09:49 AM   #19
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As I understand it, the max load will be achieved for these P-metric standard load tires is at 35 PSI, where as the max psi of the tire is 51 PSI. The max pressure does not increase the max load. And, while these tires show a rating of 108s and a max load of 2205 lbs, they must be derated to 2005 lbs because the application of the tire is on a light truck. The derating seems strange to me because I would be surprised if these tires (245/70 - r17) would be used in anything other than a light truck.

If something other than P-metric standard load tires are being used then the above does not apply.
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Old 11-20-2014, 12:06 PM   #20
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Originally Posted by CapriRacer View Post
Not quite. Sometimes the max load and the max pressure are listed as separate items. Further, the maximum allowable pressure is NOT the pressure where the load carrying capacity maxes out.

But sometimes, the pressure where the load carrying capacity maxes out IS listed on the sidewall.

It's confusing and inconsistent, but that is the way it is.
In this particular instance his sidewall shows max pressure at 51psi and has a stated max load rating printed on the sidewall so he does not have a standard P metric rated passenger car tire that has a industry standard rating of 35 psi max load rating.
His max load capacity is achieved at 51psi as stated on the sidewall.
Running less that max 51 psi will reduce his stated tire load capacity.
I believe you have a Load Range C tire and not a standard rated P metric tire.Look on the sidewall and it should be stated close to the rim bead.
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Old 11-20-2014, 01:13 PM   #21
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I basically have these:

Pathfinder Sport SA/T

Overview

The Pathfinder Sport SA/T light truck design combines a smart balance of on-road handling and off-road traction. The durable, specialized tread compound resists chipping and cutting during off-road adventures and is backed by a 60,000-mile warranty. The tire's winter rating assures reliable traction year-round. The Pathfinder Sport SA/T is available in PLT and LT sizes ranging from 15 to 18 inches.

Ratings, reviews and specifications for Pathfinder Sport S A/T tires

I guess, according to this I could have either P or LT...
http://www.discounttiredirect.com/di...=Sport+S+A%2FT

I'll have to go look at the tires again...
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Old 11-20-2014, 01:46 PM   #22
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I'll have to go look at the tires again...
Yes, these are P-rated tires - I looked near the rim at the bead and it says P245...
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Old 11-20-2014, 01:57 PM   #23
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It should have a Load Range letter listed on the tire sidewall as I mentioned.


These appear to be LT tires not passenger tires.
That is why they have a higher Max pressure.
You would not want to run these at 35 PSI pulling your trailer.
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Old 11-20-2014, 02:24 PM   #24
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My understanding is that there is no load range letter because these are P-rated tires. The tires do have a 108s for load index + speed rating. I would tend to agree that I would want higher pressure than 35 PSI when towing, but, based on my recent education on this subject from Capri Racer and Black Aces - 35 PSI is where the max load is designated for these tires. Higher PSI may change other variables of tire handling both for better and worse but not so much max load.

That said, I'm no expert; that's why I asked the question regarding all of these numbers...
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Old 11-20-2014, 03:15 PM   #25
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They are both incorrect in this particular instance.Your tires are not standard P metric passenger car tires that they are describing.
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Old 11-21-2014, 07:17 AM   #26
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I see the problem. It is here:

Quote:
Originally Posted by Moflash View Post
In this particular instance his sidewall shows max pressure at 51psi and has a stated max load rating printed on the sidewall so he does not have a standard P metric rated passenger car tire that has a industry standard rating of 35 psi max load rating.......
I'm sorry, but that is not true.

P metric tires are indeed maxed out loadwise at 35 psi - BUT - it is permissible to use higher pressures and to accommodate those, the tires will frequently quote max pressures of 44 psi or 51 psi, depending on what the tire manufacturer deems appropriate.

This way of doing things is unique to P type tires - both P metric and hard metric.

LT, ST, and other types of tires don't do things that way. They state the max load at the corresponding pressure - and don't state that pressure as a maximum. In fact you can use higher inflation pressures on those other kinds of tires, but it doesn't say so on the sidewall. It only describes a relationship.

So go to your car and check out what those tires say.
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Old 11-21-2014, 11:28 AM   #27
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It seems like moflash is stating that, "Your tires are not standard P metric passenger car tires that they are describing." and that Capri Racer and Black Aces are saying that these are, in fact, standard P-metric tires. I don't think we will have any agreement until that is resolved.

My guess is that these are standard p-metric tires based on the P245 near the rim and the load and speed rating. The tires have no ply-rating (but I don't know if there is a default value for non-rated tires). The tires also say that they are standard load which is a designation for p-metric tires that does not seem to exist for LT tires.

On the other hand, Moflash might not be saying these are LT tires, he may just be saying that these are not the standard kind of p-metric tires. I don't know how to evaluate that statement.

Which, of course, is why I started this thread to begin with - I don't understand the nuance of tires, tire-rating, tire-design, the relationship between tire pressure and load, and the various trade-offs thereof. The other question was - am I safe - and I think the answer to that is yes.
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Old 11-22-2014, 05:15 AM   #28
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........The other question was - am I safe - and I think the answer to that is yes.
I should have done this when you first posted, but there are some possibilities you are not safe. - but we don't know, because we don't know enough about your truck to determine it.

First, go to your driver's door and look at the vehicle tire placard. It will tell you the original tire size and the proper pressure for that size - and then tell us what it says.

In the process of trying to answer this question, I made some assumptions, and discovered there is quite a range of tires that came on F-150's - and it's possible that you could have the wrong kind of tire on your truck - and it is possible everything is fine.

Also, I am not a fan of odd brand tires. As it turns out, you did give us enough information to figure out who made them - Kumho. They are a greatly expanding Korean tire manufacturer, so I don't have any concerns there. But keep in mind that odd brand tires aren't always made the most reputable tire manufacturers.

*******************

Edit:

Further down the thread you told us that the OE tires were P235/75R17 and the tires currently on the truck are P245/70R17. While that isn't the same, those are more or less equivalent.

So, I guess you are OK.
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