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Old 11-15-2007, 06:55 PM   #1
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Tires 101

Hi folks.

Last week I had one of those dread weeks at work. Some of you in the technology field can relate. Work some in the daylight, then come back in and work all night doing software upgrades and moves between servers. Incredibly exciting stuff that consists mostly of starting a software load and waiting an hour for the server to do its thing. Anyway, in the midst of all this boredom, I was able to do some reading here on the forum. Tires. Maybe the only subject less exciting than say, watching paint dry, ordering hardware or watching the progress meter on a server upgrade.

Somewhere around the middle of the night (can’t remember which day, they all seemed to run together) I had an idea. There are many threads here concerning tires for our Airstreams. A couple of really good ones like this: Tire stuff. The problem is that you have to wade thru pages of opinions on the subject and posts that assume you understand the terminology and concepts. Sorry, I’m still just a rookie. What I know about my Airstream tires can be summed up thusly: They are made of some kind of rubber compound and were once more or less round. Oh yeah, they need to be replaced. Apologies to Jean Shepherd.

So here’s the pseudo-official rules. No Highjackin' by bashin’ your least favorite country of tire origin. No arguin’, try and keep the opinions to a minimum, just the facts ma’am. And please, explain the concepts in terms even I can understand.

Humor is welcomed, nay, encouraged! A subject as dry as this needs something to prop it up!

So here’s the first question for somebody in the know: What I know about “Load Range” has to do with how much junk you can pack into the bed of a truck and carry it down range for a while. Presumably, the further up the alphabet you go, the more weight a tire can handle. Is there really a load range “C” and is it useful?

Thanks in advance for the replies. Your turn.

Jim
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Old 11-15-2007, 07:38 PM   #2
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Originally Posted by Jim & Susan
. . . can be summed up thusly: They are made of some kind of rubber compound and were once more or less round.
Jim
Some are made out of polyurethane.

I've heard that moving servers is just like moving toasters. You just unplug them over there and plug them back in over here. Pretty simple.
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Old 11-15-2007, 07:45 PM   #3
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Originally Posted by markdoane
....I've heard that moving servers is just like moving toasters. You just unplug them over there and plug them back in over here. Pretty simple.
Unless they're Sun 1290's, then you have to get a work permit form the Gov'ment and three very hefty guys to help lift the danged heavy things.
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Old 11-15-2007, 08:23 PM   #4
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Mine are Load Range C tires:

Yokohama RY215 in 7.00 x 15 radial. A long-time trailer size, roughly comparable to 235/75-15 (a wider tire)

An LT tire with 65-psi max cold rating, at 2,040-lbs. This range is what is specified in my 1983 Owners Manual (Silver Streak Trailer Co.); the original size recommendation is H78-15. They are currently at 90% of gross, and, what with a reasonably conservative rating by Yokohama, I expect long life from them.

I purchased this tire through DISCOUNT TIRE (who, in turn, ordered it from The Tire Rack; size 7R-15 ). After mounting, they all balanced out on a HUNTER GSP-9700 to 24-ozs or less ("Road Force Balancing"). I mounted them myself with new heat-treat lug nuts against CENTRAMATIC Wheel Balancers. I retighten nuts before every trip, and keep tires at a "perfect" 65-psi cold.

The tires run about 90-95F on a 75-85F day (Interstate; 63-mph, 7,400# trailer), and 125-130F on a 100F day (same). The trailer tracks well in all conditions (no heavy rain, yet, to check braking), and has no trouble about picking up gravel/stones.

A nice, heavy-duty commercial tire.

The specs on the tires are:

29.4" tall
4.9" tread width
7.7" section width on a 6" rim
tire weighs 32#
tread depth is 13/32"

I'm a believer in staying very close to the manufacturers recommendation (not as simple as it sounds) as their experience and testing tends to cover the majority of situations in re durability, safety and reliability.

One may educate oneself quite easily these days via the Internet. The above two retailers have good info (especially T-R) and the manufacturers websites are also good, if not in great depth. You are correct that tires have a good deal of "science" in them, and the folks I've talked with who have business or racing interests often have fine insights.

As to trailer tires -- what with the "standard" disappointments of the past few years vis-a-vis ST tires -- one is still advised to inspect tires before, during and after any trip, every day on the road. And on a regular schedule when off. Similar to truck/bus drivers, pilots, etc. No matter the tire brand or size (perfectly stock, brand-stinkin' new), the owner MUST exercise caution, control and care.

I think what is a bit off-putting about trailer tires is that one cannot really hear, feel or even see them while going down the road; there is no "relationship", no positive or negative feedback. Thus, my attitude towards them is to do as much as possible (see Andy/Inland RV Ctr posts and company website about balancing, for instance), replace them often (a few years, hopefully many miles), and keep them clean and shiny as I also inspect suspension, brakes, hubs and wheels . . .

. . then, if I lose one, it is more to bad luck than p-poor attitude and practices. A blown tire can really take the pleasure out of a trip; I find that "unscheduled maintenance" (on the side of the road) tends to reverberate for a few days. And, it causes me to question myself which is not the reason I am on the road with the trailer.

Take care.
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Old 11-16-2007, 12:37 AM   #5
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Jim,

Here's a try at your load range question. The letters are an attempt to simply the tire selection process for Americans.

Over simplified ----
LR "B", 35psi, is passenger cars for good ride
LR "C", 50psi, is light truck (150/1500vans & pickups) for good ride
LR "D", 65psi, is light truck (150/1500/2500 vans & pickups)for hauling/work vans,15 pass vans, & pickups
LR "E", 80psi, is light truck (250/350/3500 vans & pickups) for heavy towing & hauling

"light truck" is probably a misused term. A guy driving a class 8 tractor trailer running at 80,000 lbs thinks vans & pickups are light. And the industry does too.

Detroit is in a weight race right now and the lines between 1500/2500/2500HD/3500 are very blurred.

LR "C" is a bit more complicated.

I think you would find that a LT LR C ( light truck load range c) tire as compared to a LR B (pass) would have
(1) more turns of wire in each bead
(2) probably a slightly larger carcass fabric, still 2 plies
(3) more carcass fabric wrapping around the bead with a gum filler inside the wraparound area
(4) larger dia. belt wires
(5) possibly a 3rd belt either wire or fabric
(6) heavier tubeless liner for higher air pressure
(7) heavier tread for deeper traction bars

I have summarized a table as follows: From Goodyear
"B" 35psi 1760 lbs
40psi 1990 lbs
45psi 2020 lbs
"C" 50psi 2150 lbs
55psi 2270 lbs
60psi 2380 lbs
"D" 65psi 2540 lbs

I hope this answers your question.

In my case, I like to caravan & the leader insists on full water tanks plus we haul cook stove, table, air pump, tools, jumpers, etc. and we can exceed 7300 lbs. The trailer had LR C's when I bought it but, I have replaced them with the Marathon LR D's. Therefore at 65psi cold, I am at 7300lbs-600 for hitch on truck or 6700lbs/4 = 1675lbs/tire / by 2540 = 66% load factor.
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Old 11-16-2007, 11:44 AM   #6
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Size Primer

Also, in case you didn't already know this, is how the sizes work:

235/75-15

235 is the section width of the tire in mm, so measure from outside of one sidewall to the outside of the other sidewall and it should measure 235mm, that's before it squishes under the weight of the vehicle.

The 75 is the aspect ratio of the tire in percent. That means if you measure from the edge of teh wheel to the outside of the tire, that distance is 75% of the section width. So in our example, from the top of the rim to the top of the tire is 0.75 * 235mm = 176mm.

The 15 is the diameter of the rim in inches.

So to compute the height/overall diameter of the tire, you get:
D = ( ( 2 * Aspect Ratio * Section Width ) / 25.4 ) = 15

The 25.4 converts the mm to inches, and you have twice the aspect ratio because you have that amount of rubber under the rim and above it.

So the height of our example is 2*.75*235/25.4 + 15 = 27.88"

Now in the older standard way of measuring, a 31x10.50-15 is a little easier; the tire is 31" tall, 10.5" wide, and on a 15" rim.

A 7.00R15 doesn't tell you anything; you just have to look it up.

Hope this helps,
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Old 11-16-2007, 06:13 PM   #7
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Thanks guys, this is exactly the kind of information I was hoping we could get here. Karma coming at ya!

So here's my next question. I bought a set of pick up truck tires last year for the F150. On the sidewall of the tire are a bunch of numbers and letters after the "DOT" stamp. The last four numbers of that alphanumeric string are "1006". Am I correct in understanding that this indicates these tires were manufactured in the 10th week of 2006? Did this "code" change in the last few years? It seems like I remember reading the manufacturer date code used to be fairly straight forward, 4 digits indicating the week and year the tires were made. Now, there is a bunch of extra stuff in the string. Can anybody decode those, or does it matter to me what all that stuff means?

Thanks for the help! Your turn.

Jim
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Old 11-17-2007, 02:38 PM   #8
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It's the data used to track the worker down in case of a blow out. So they know who to fire.

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Old 11-17-2007, 08:59 PM   #9
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Secret decoder ring discovered

All those letters do actually mean something.

From the NHTSA website (and in plain English!):

U.S. DOT Tire Identification Number
This begins with the letters "DOT" and indicates that the tire meets all federal standards. The next two numbers or letters are the plant code where it was manufactured, and the last four numbers represent the week and year the tire was built. For example, the numbers 3197 means the 31st week of 1997. The other numbers are marketing codes used at the manufacturer's discretion. This information is used to contact consumers if a tire defect requires a recall.

Heres the link if you want to read all that stuff: Tire Safety, Brochure (DOT HS 809 361 October 2001)

Jim
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Old 11-20-2007, 08:56 PM   #10
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Somewhere on one of a gazillion tire threads I asked the question: what's the difference between LT and trailer tires. The answer: trailer tires have stronger sidewalls. I think it came from either Andy or lewster. I take no credit. If Discount Tire (#4 above) is recommending LT for a trailer, I wonder about that. I buy tires from them in Grand Jct., but am really careful about what they tell me.

I also take no credit for a suggestion that a microphone be installed next to the tires so we could hear: "ssssss, blam, flap, flap, crash". I did do the dialogue though.
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Old 11-20-2007, 10:09 PM   #11
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Hisssssss.... away, Gene! That's kinda why I started this thread, to seperate fact from opinion. And that was my next question also:

LR stands for "Load Range"
LT stands for "Light Truck"

I seem to remember a few others like (maybe) SR? or RT? Maybe I'm not remembering it right. Can anybody fill in the blanks?

Jim
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Old 11-20-2007, 10:25 PM   #12
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CrawfordGene,

I have read something similar on two or three threads on this site. Namely, that ST trailer tires have stronger sidewalls, etc, etc.

That is probably true if they are comparing to passenger tires but, a comparison to a real LR "C" or "D" Light Truck Tire, it is highly unlikely. "Stronger sidewalls" is really a misnomer. A light truck tire should have heavier bead wire, more ply fabric wrapped around the bead, and a filler inside the ply fabric wrap around area. These items should make the sidewall at least as strong as an ST trailer tire.

The only construction item that an ST tire has that might make it better than an LT tire is a "belt edge reinforcement". This is a 1" nylon strip that runs circumferentially around the tire and is located at the edge of the belts. These nylon strips (one on each side) help to hold the belt edges and prevent tiny cracks from starting at the edges of the belts due to stress, heat, speed, etc. Belt separations & tread separations probably start at the edge of the belts in most cases.

With the exception of the belt edge reinforcement, I would expect the materials & construction in LT tires to be superior to trailer tires. Why? Because the LT has to stand up to front wheel steering inputs, drive wheel torque and I am fairly certain they are tested to 80mph.

All trailer tires do is roll, brake, & take some side load when turning plus they are only rated to 65mph.

A really good tire dealer should be able to take a person through the differences in construction that does not get labeled on the side of the tire.
If they can't, their people have not been sent to the various schools that all major manufacturers hold.

The major manufacturers should be very close to each other. They buy each others tires & cut & analyze them so there are very few secrets.

I was not a tire engineer but, spent quite a few years in the business.
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Old 11-20-2007, 10:48 PM   #13
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So ST stands for "Special Trailer" tire?
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Old 11-20-2007, 10:48 PM   #14
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Wing, Do you know of a source that can confirm what you are saying in post 12? Everything you say there, logically, makes perfect sense. Still, there are are those who mount truck tires on their trailer axles. I can only assume that they have a belief that the truck tires are somehow superior to the trailer tires.

Jim
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