Tired?

OK, This post has nothing to do with herbs.

For some of you this may be boring, for some it may be interesting, for some it may be a review, but I wanted to share it.

We had to replace the tires on both of our vehicles this week. They have both been riding on a wing and a prayer for several thousand miles. The Original Equipment tires for our F150 were rated for 40,000 miles and we just passed 60,000 on them.

As for the tires on the Ranger, I have no idea how many miles they had, but they were dry rotted so bad that they were starting to leak, and I had to keep adding air to two of them. We put it off long enough. It was time to bite the proverbial bullet and buy new tires.

Some things to keep in mind when buying tires.

When comparing the cost of tires between different dealers, make sure and ask for "out the door" pricing.

Some shops will charge you for mounting, balancing, valve stems, old tire disposal, and anything else they can sneak in, while others will just charge a flat rate for tires. This is important to know when comparing prices.

For example. WalMart sells tires. They charge $5 to mount and balance, $2 for new valve stems, (they won't mount a new tire without a new stem) and $1.50 to throw away your old tire. So there is a minimum of $8.50 per tire added on to the price they quote you. They also do not include sales tax in their quote. So, a tire that they sell for $100 will cost you "out the door" $114.51. That $14.51 doesn't seem like that much until you multiply it by 4.

If a Mom & Pop shop tells you $450.00 out the door, for four tires and Walmart tells you the tires are $100 each, the Mom & Pop shop costs less.

The most important thing to remember however, above anything else, and I cannot stress this enough.
Never, ever let a salesman sell you a tire with a lower service description than your vehicle had originally. Even if they have them on sale, for a really great price, this is never a good deal.

How do you know your service description? It's one of that big string of numbers on the side of the tire. Have you ever looked at all those numbers and wondered what they mean?

Because I delivered tires for years, all those numbers made sense to me, but it occurred to me, as I was tire shopping, that not everyone delivers tires for a living. Before I had that job, those numbers would have all just been a meaningless stream of mumbo jumbo.

So, let's take a minute and explore the number on the side of a tire.

Our F150 Tires are P265/70R17 100S

For those who like secret codes, get your Goodyear Decoder Ring and lets go to work. First let's break the string up a little.

P -- 265 -- 70 -- R -- 17 -- 100 -- S

Now lets go to work:

The first letter indicates the service type, or what the tire is intended to be used for.

P = Passenger tires.
They could also say "LT" for Light Truck.

The difference between Passenger and Light Truck Tires, is the thickness of the rubber in the sidewall of the tire. An LT tire has a thicker sidewall and can hold more air. This allows your truck to carry more weight without damaging your tires. If you haul a lot of weight, if you use your truck for industrial work, or if you pull a fifth wheel trailer, LT tires may be a better choice.

If you use your truck mostly for light hauling, P Metric tires (as they are commonly called) will do the job just as well, and, as they have less rubber in the sidewalls, they will be a little more flexible and therefore will ride a little smoother.

If the first letter is a "T", these are temporary tires, such as an emergency spare, and are not intended for long term use or for highway speeds. (In the tire industry, these Mini spares are often referred to as Donuts)

"ST" indicates a Special Trailer tire, designed for use on a trailer. These tires should never be used on cars or trucks.

There may not be a letter at all. In that case, you probably have a Euro-Metric tire. Although they are used mostly in Europe, a few have found their way here, mostly on mid sized SUVs and mini vans. Euro-Metric tires are comparable to "P" metric tires, with only very minor weight differences.

The next number is the tread width.

265 - Means that the tire is 265 Millimeters across. This is the measurement of the amount of tire that touches the road, and not, as some people believe the width of the tire from sidewall to sidewall.

For those of us non metric people, 300 millimeters is about a foot, so 265 is about 10 inches. Those of you who are perfectionists can figure it our exactly if you want, but for most of us, That's close enough.

The next number is known as the Aspect Ratio.

This is a fancy term for the height of the sidewall, or the distance from the road to the rim. This number is a percentage of the tread width, so 70 means that the sidewalls of my tires are 70% of 10 inches, or about 7 inches tall.

The R indicates that these are Radial tires.

This used to be much more relevant than it is today. Most tires on the road today are radials.

This is a reference to the internal construction of the tire. There are cords, generally steel or fiberglass that run back and forth inside the tire and add strength. Radial tires have those cords running straight across the tire, while Bias ply tires have the cords running diagonal and criss crossing.

Radial tires get better fuel economy, and wear longer, since the cords do not rub back and forth against each other as the tire spins. Bias tires are almost obsolete.

The next number is the rim size.

For whatever reason, tires are measured in millimeters, but rims are measured in inches, so 17 means my rims are 17 inches across.

I was never much of an artist, but this may help:


The final numbers are what is known as the Service Description

The first part is the weight capacity and the second is the speed rating.

There are charts and tables available to break down service description codes, in fact you can find a good one, (and a lot of other helpful tire information) here
Click Me

By looking it up on the chart, I can see that the 100 S on my tires means that each tire can carry up to 1764 pounds and be safe at speeds up to 112 miles per hour.

If I ever decide to drive faster than 112 mph, I will run the risk of overheating my tires. My tires are simply not capable of dissipating heat at speeds higher than 112 mph.

Of course I also run the risk of getting a ticket, losing my license and having my wife take my truck keys away, but those are all insignificant when compared to a blowout at over 100 mph.

So, to recap,

P265/70R17100S Breaks down like this:

P..........Means my tires are designed to be used for standard highway use,
265/70......are about 10 inches wide and about 31 " tall (7+17+7)
R...........are radial tires
17..........Have a 17 inch opening in the center
100......And should be safe carrying a vehicle no more than 7056 lbs (1764 X 4) S ..........at speeds of less than 112 miles per hour.

Now that you understand my tires, you should be able to figure out your own. Armed with a basic understanding of what the numbers mean, you should be better equipped next time you have to go to the tire store. Remember, knowledge is power.

And the most important thing to remember? Above everything else, do not EVER put tires on your vehicle that have a lower service description code than the original tires.

If you do, your tires will not be designed to carry the weight of the car at the speed the car is designed to run.

Putting a lower Service Description tire on a car is like asking for a blowout.

As for the rest of the numbers, be familiar with what they mean on a general basis, but a good rule of thumb is to just buy the same size, and type that the vehicle came with.

You can find more helpful information about tires at these places:

How Stuff Works

Tire Tech, Tire Info.

If you want help with metric conversions, a handy guide can be found here: