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Old 11-05-2014, 01:22 PM   #1
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So many numbers on tires...

OK, so I find the numbers on the tires for my truck a bit confusing. I am hoping I am towing safely... So I have a 2012 Ford F150 Ecoboost (4x4, supercab) with Pathfinder S A/T 245/70 - r17 tires. Then there is a whole bunch of other information that I suppose is supposed to be informative to me but I am having trouble figuring anything out... that A/T - does that mean All Terrain? And, what the heck does all terrain even mean? How does that compare to any other category? What are the other categories? OK, after the 245/70/r17 it says 108s (does that mean something)? I have a DOT information - but I can't figure out much about that either DOT H2CS YP5T (4513?). The tires have traction rating: A and Temperature rating: B. Is that meaningful in some way? And, I don't mean meaningful, in general, I mean meaningful in the sense that it would have an effect on towing performance for me... I have two pieces of information regarding plies - Tread Ply: 2 steel + 2 poly + 1 nylon, and sidewall ply: 2 ply poly. Is this OK? And, well, I see that the Max Load is 2205 lbs and the max pressure is 51 psi. From what I can tell, this is just fine - the vehicle has 5,476 pounds base curb weight, 1,660 payload capacity and 7,200 gross vehicle weight rating (GVWR). So, if I'm getting 2205 lbs of max load from each tire that will more than exceed the GVWR, so if I'm doing that I'm in trouble anyway. These aren't the numbers from the actual vehicle, but from the spec sheet, but I know when I've looked at the actual vehicle numbers they were very similar to the spec sheet numbers as well.

I bought the truck used, the tires look reasonably new - so my goal is to not change the tires without cause. That said, do I have cause?

For the record, I'm towing a 2012 20 foot flying cloud - so not a large trailer anyway...

Anyway, I did make some effort in trying to figure this out - and then I simply became more exasperated.

Thanks, in advance.
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Old 11-05-2014, 01:32 PM   #2
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http://m.discounttire.com/dtcs/infoSidewall.do


Everything you wanted to know about tire codes but were afraid to ask :-)
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Old 11-05-2014, 01:53 PM   #3
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About the only answer you won't find on the Discount Tire site above is the definition of AT. AT does mean "All Terrain" as you suspect. What does that mean? Not a whole lot really since I believe that it is a marketing gimmick that means the tires are "nobbier" than "usual" signifying their supposed ability to pull your truck out of the muck (good luck with that!) My experience with AT tires on previous trucks is that they are louder than standard tires due to the "nobbiness" and can wear out faster. But otherwise they should be fine for you to use while towing.
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Old 11-05-2014, 03:03 PM   #4
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OK, so, based on the above, I guess there is one other question, the 108 S after the size - I guess that is not meaningful or makes no meaningful difference? The guide says after size info there may be something like /E. after mine there is no slash but there is 108 S. I suppose that means, I have a four-ply rated tire (interestingly enough, the number of plies rating is not indicative of the actual number of plies...). The person I bought the Flying Cloud from said that I should get E rated tires because, in case of a failure, they are safer. Does the Airstream community have a general stated preferences for ten ply tires over, say, four? And, would it make a difference vis-a-vis my 20 foot flying cloud vs. a 34 foot behemoth?

The tires on the truck say "Standard Load" but I don't know if that means I should or should not be towing with them. It could be that Standard Load means good for the purposes of the vehicle it was purchased for (like a truck which tows things) or it could mean something like not so safe to tow with. Based on the capacity it seems fine. If the max pressure yields more than the max load of the vehicle's GVWR, should I lower the pressure to something less than max? What is the tradeoff between max pressure and all other variables? (I don't even know what the other variables are...). I also don't know what the equation is - there must be something that says for this weight the pressure should be x. Is going over the x value (optimum tire pressure for weight per tire) bad?

And, what are the other categories? This is AT - so all terrain - but is there like performance, towing, and the most excellent categories? I see above that AT is, perhaps, just marketing speak...

Really, I started to get concerned about all of this after reading a different tire thread that suggested voiding warranties via using tires of unintended applications was, perhaps, bad...

That said, well, I've towed the camper more than a couple of times and everything seems fine... You can tell me I'm over-thinking this whole thing...
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Old 11-05-2014, 03:57 PM   #5
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I think you will be fine with these tires on your F-150.

Ratings, reviews and specifications for Pathfinder Sport S A/T tires
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Old 11-05-2014, 05:53 PM   #6
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Ah 108 S is load index + speed rating. In this case 108 load index = 2205 lbs and speed rating (S) = up to 112 mph. I think the truck is limited to 100 mph anyway (and I'm not going there as it is)...
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Old 11-06-2014, 07:13 AM   #7
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Quote:
Originally Posted by ukulele2010 View Post
Ah 108 S is load index + speed rating. In this case 108 load index = 2205 lbs and speed rating (S) = up to 112 mph. I think the truck is limited to 100 mph anyway (and I'm not going there as it is)...
Most prudent drivers like to keep their maximum speed to between 60 & 65 mph anyway, some even under 60. Bad stuff happens very quickly at 70 mph+!
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Old 11-06-2014, 07:13 AM   #8
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I will only be answer the questions you don't already have answers on:

Quote:
Originally Posted by ukulele2010 View Post
........The guide says after size info there may be something like /E. after mine there is no slash but there is 108 S. I suppose that means, I have a four-ply rated tire (interestingly enough, the number of plies rating is not indicative of the actual number of plies...).......
You should get rid of the idea that the number of plies is indicative of anything. There are tires made with a single ply that are rated like 50 plies - that's because the ply is made of steel.

Instead you should think in terms of load carrying capacity - that's what the load index is all about. Your truck is going to have a sticker on the driver's doorframe that will list the original tire size and the proper inflation pressure for that size. This sticker is called the vehicle tire placard - (just placard for short.) Note that after the tire size will be the service description - the 108S.

If you use the inflation pressure listed there and tow within the limitations published by Ford, you should be fine. Don't listen to anyone who says to use the pressure listed on the sidewall. That's a maximum (even says so), and NOT a recommendation.

Quote:
Originally Posted by ukulele2010 View Post
........ The person I bought the Flying Cloud from said that I should get E rated tires because, in case of a failure, they are safer. Does the Airstream community have a general stated preferences for ten ply tires over, say, four? And, would it make a difference vis-a-vis my 20 foot flying cloud vs. a 34 foot behemoth?.........
Again, you shouldn't listen to everyone who gives you advice. Some folks have faulty information, but like to think they don't.

I am NOT a fan of replacing P type tires with LT type tires (which is what the former owner is suggesting). LT tires require 15 psi more to carry the same load as a P type tire. I can understand why people think that might be a good idea, but I think that line of thinking is faulty.

Quote:
Originally Posted by ukulele2010 View Post
........The tires on the truck say "Standard Load" but I don't know if that means I should or should not be towing with them. It could be that Standard Load means good for the purposes of the vehicle it was purchased for (like a truck which tows things) or it could mean something like not so safe to tow with.......
P type tires come in Standard Load (SL) and Extra Load (XL). The difference is that XL tires can carry more load, but you need more inflation pressure to do that.

Please note that Ford specified the size and inflation pressure such that if you use the truck within the limitations published, the truck should work fine.

Quote:
Originally Posted by ukulele2010 View Post
........ Based on the capacity it seems fine. If the max pressure yields more than the max load of the vehicle's GVWR, should I lower the pressure to something less than max? What is the tradeoff between max pressure and all other variables? (I don't even know what the other variables are...). I also don't know what the equation is - there must be something that says for this weight the pressure should be x. Is going over the x value (optimum tire pressure for weight per tire) bad?........
A tire's load carrying capacity is a function of its size and the inflation pressure. (and a couple of other things as well that we won't get into.) There is a formula, but it is complicated, so charts are published with the values

- BUT -

You don't need to bother with the formula or the charts as Ford has told you what tire size you need and what inflation pressure to use.

And a side note: Tire wear is not particularly sensitive to inflation pressure, but load carrying capacity is. It is OK to run tires over what the charts say is the minimum pressure for the load you are carrying. If you have wear issues, it is much more likely caused by something else.

Quote:
Originally Posted by ukulele2010 View Post
........And, what are the other categories? This is AT - so all terrain - but is there like performance, towing, and the most excellent categories? I see above that AT is, perhaps, just marketing speak.......
The term All Terrain means what it says. The tire is designed to be used both on road surfaces (concrete, asphalt) as well as gravel, and dirt roads. It is a compromise between All Season (which are designed to be used year round on paved surfaces), and Off Road (which are not designed for use on paved surfaces.)The categories aren't well defined. They are guidelines to help select the proper tire for your intended use.

Oh and do NOT pay attention when the letters appear in the name of the tire. A tire could be named with the letters "A/T" and that is just to distinguish it from the one named "ST" or "AS", or whatever.
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Originally Posted by ukulele2010 View Post
........Really, I started to get concerned about all of this after reading a different tire thread that suggested voiding warranties via using tires of unintended applications was, perhaps, bad......

That said, well, I've towed the camper more than a couple of times and everything seems fine... You can tell me I'm over-thinking this whole thing...
Yup, but keep asking questions. That's the only way to learn.
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Old 11-06-2014, 11:47 AM   #9
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DOT number 4513 means the tires were manufactured in the 45th week (November 8-14) of 2013. Must be a new truck.
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Old 11-06-2014, 12:28 PM   #10
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The truck is a 2012 F-150 with about 75k miles. We bought it used but does indicate that the tires were changed sometime after November 2013. It's a lot of miles for a two year old truck. So we have passenger tires? How do passenger tires differ from light truck tires? I see, of course, that light truck tires have different ply ratings - but, as noted, that may not be very important for this application given the load rating of the tires (108 or 2205 lbs). These passenger tires do have a specified load rating on them (at a given PSI). When I look at the tire rack descriptions they state that passenger tires of standard load type have a max PSI of 35 - but clearly that is not the case for these tires (stated 51 PSI).

The OEM tires were 235/75 R17 - these replacement tires are 245/70 R17. My guess is that there isn't much of a difference... If my calculations are correct it is a 2.8% size difference (which may explain why the speedometer and the gps don't agree on speed ). Someone probably bought these tires not so much for performance, but for price (value)...

Oh, and, yes, I tow around 60-65 mph - the speed rating would be may be more important without towing. I can't imagine that the truck is very responsive, in general, and going fast is will not make anything better. The speed limits in Colorado go up to 75 mph and without towing I would probably manage to do that. And, I'm limited - I can't do more than 100 as the vehicle is governed.

Ref - max psi of passenger tires - standard load:
http://www.tirerack.com/tires/tirete....jsp?techid=55
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Old 11-06-2014, 01:52 PM   #11
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Tire Age Code

One very important thing that nobody covered above (unless I missed it) was the DOT age or mfgr date code:

"I have a DOT information - but I can't figure out much about that either DOT H2CS YP5T (4513?)."

45 = week of the year (note that just one day 1/1 will count as week #1)

13 = 2013 year

So those tires are relatively new mfgr'd about November-ish (52-45 = 8 weeks).

Cars & trucks are recommended to be let go no more than 7 or 8 years old - sooner change if sidewalls &/or tread has cracks, tread down, etc.

I've been recco'd by trailer pro's to only go 5 years on the trailer tires (whether you're using ST trailer tires or LT light truck ones), with the same wear & cracking caveats.

Cheers!
Tom (the other half)
///////

PS - the Tire Rack & most tire websites have good explanatory info on all this inf - many with good pix.

Some also have the online calculator to compare tire sizes for speedometer/odometer error.
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Old 11-07-2014, 07:21 AM   #12
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Quote:
Originally Posted by ukulele2010 View Post
.......So we have passenger tires? How do passenger tires differ from light truck tires?........
Basically the difference is about load carrying capacity. LT type tires are designed for higher load carrying capacity than P type tires. There is obviously a crossover area where large P type tires have more load carrying capacity than small LT's - but the principle is there..

Also, there is a fundamentally difference in the way those 2 type are designed. LT type tires use high unit loading - that is, a high load carrying capacity compared to their physical dimensions. They do that by using high inflation pressures.

Quote:
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....... When I look at the Tire Rack's descriptions they state that passenger tires of standard load type have a max PSI of 35 - but clearly that is not the case for these tires (stated 51 PSI). .........
Uh ...... Mmmmmmm ......... not exactly.

I think you'll find that Tire Rack says that the load carrying capacity of passenger car tires (SL) maxes out at 35 psi. - and that there may be some situations where more pressure is suggested, such as higher speeds, hence the maximum pressure listed on the sidewall being higher than 35 psi.

Quote:
Originally Posted by ukulele2010 View Post
.......The OEM tires were 235/75 R17 - these replacement tires are 245/70 R17. My guess is that there isn't much of a difference......
There isn't much difference, but there are some. As you point out, there is a difference in rolling diameter - among others.

Quote:
Originally Posted by ukulele2010 View Post
.......
Ref - max psi of passenger tires - standard load:
http://www.tirerack.com/tires/tirete....jsp?techid=55
Yup, just as I suspected. Tire Rack talks about max load and what pressure that occurs at, not what the max pressure is.
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Old 11-07-2014, 12:07 PM   #13
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Ack! OK, so yes, I fundamentally misunderstood max pressure (PSI) and max load pressure. So, the my tires say max load 2205 lbs and max pressure 51 PSI. But my maximum load pressure is 35 PSI because I have a passenger/standard load tire? That is, I can carry the largest load for the tire at 35 PSI? And, how does an increase of PSI will change the maximum load performance (or characteristics of the tire/truck performance)? Or is this that maximum load requires a minimum of 35 PSI? How does increasing the PSI beyond 35 affect anything? That is, I really don't know the relationship between tire pressure and carrying capacity - is it an increasing function (more psi - better load capacity)? Is it u-shaped (beyond a certain point it, more psi - better load capacity)? or upside-down -u-shaped - optimum at some value, then decreasing at greater psi. All of these questions are for psi within the allowable range...
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Old 11-08-2014, 06:08 AM   #14
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Quote:
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......So, the my tires say max load 2205 lbs and max pressure 51 PSI. But my maximum load pressure is 35 PSI because I have a passenger/standard load tire?........
That is correct.

Quote:
Originally Posted by ukulele2010 View Post
...... That is, I can carry the largest load for the tire at 35 PSI? And, how does an increase of PSI will change the maximum load performance (or characteristics of the tire/truck performance)?..........
It's a little complicated, and there are a lot of things affected, but the short answer is that it has no affect on load carrying capacity.

Quote:
Originally Posted by ukulele2010 View Post
......Or is this that maximum load requires a minimum of 35 PSI?........
Yes, that is part of the reason it is a bit complicated.

Quote:
Originally Posted by ukulele2010 View Post
...... How does increasing the PSI beyond 35 affect anything?......
Well it stiffens the tire giving a more precise feel, but increases the harshness of the ride. It also improves the speed capability - up to a point (just like what happens with load carrying capacity).

Quote:
Originally Posted by ukulele2010 View Post
...... That is, I really don't know the relationship between tire pressure and carrying capacity - is it an increasing function (more psi - better load capacity)?.......
Yes

Quote:
Originally Posted by ukulele2010 View Post
......Is it u-shaped (beyond a certain point it, more psi - better load capacity)?.....
Absolutely not.

Quote:
Originally Posted by ukulele2010 View Post
...... or upside-down -u-shaped - optimum at some value, then decreasing at greater psi.....
Yes, which is why the load charts stop at 35 psi for SL P metric tires. The tire manufacturers don't want you to worry about what happens above that value, but it does slowly drop off.

Suffice it to say, the relationship of load to pressure is more or less a a straight line that does not go through the origin, and peaks at some pressure (and load), and doesn't drop off enough to worry about after that.
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