Understanding all the numbers on my tire

WHAT DO ALL THE NUMBERS ON MY TIRE REALLY MEAN??

In this blog entry, I will attempt to explain what all of the numbers on your tires really mean. Any tire retail website will have this same information, but their explanations still seem a little "techy" I hope to explain in such a way, that anyone can understand. 

To explain passenger tires I will use the photo below of a 195/65R15 Uniroyal Touring Trak A/S for my example: On sale at www.Onlinetiredeals.com for $70.00

SIZE:

The size is the obvious place to start. That is what determines what tire will fit on your vehicle. The size for this tire is a P195/65R15.

P = passenger designation

195 = the width of the tire in mm.. 195mm = 7.677 inches

65 = a percentage of sidewall to tread width... This tire's side wall is 65% of 195mm or 126.75mm or 4.99 inches on both sides of the rim.

R = Radial construction, 99.9% of the tires manufactured these days is a radial tire

15 = rim diameter.. This tire is to be mounted on a 15" Rim

So with this information, we can calculate the overall tire diameter.. 

65% of 195mm x 2 (both sides of rim) + 15 (Rim diameter)

4.99 inches x 2 + 15 = 24.99" tall 

MYTH ON SIZE:  The middle number doesn't not indicate width. So often, people say that they want a "wider tire". Popular belief is that "I'll go with a 55 series instead of my stock 60 series for a wider stance"

Without increasing the first number, all you are doing is getting a shorter tire by lowering the 2nd number. 

For Example: 

stock size is a 225/60R16 which is 26.63" tall and 8.86" wide

assumed "wider" tire: 225/55R16 is still 8.86" wide (225mm) but now only 25.74

YOU'VE LOST ALMOST AN INCH.

However, if you go with a 245/55R16 (if such a size) you maintain the same height 26.61" but get extra width 245mm or 9.65"

SERVICE DESCRIPTION:

The load index with speed rating is known at the service description our Uniroyal is a 89H

 

LOAD INDEX:

In layman's terms, this is load carrying capacity or how much weight the tire can carry. 

Our Uniroyal above has a Load Index of 89. With out the load index chart below, this number does not mean anything. The Load Index chart was created for a consistent value among all tire manufacturers. 

As we can see from the above chart 89 = 1279 lbs

Does this mean that your car's tires can carry 1279 x 4 = 5116 lbs?

NO, NOT EXACTLY.. The values on the above chart are weights at "maximum air pressure" The maximum air pressure for this tire is 44psi. HOWEVER, although auto manufacturer recommended pressures vary, for our size 195/65R15 28-32psi is common.

SPEED RATING:

This is a speed that a tire has been tested to safely run and maintain. Although you tire may be able to run and maintain a certain speed, it is never ever recommended to drive these speeds on public roads. 

Our Uniroyal above is a H speed rating (the speed rating always follows the load index value)

As we can tell from the following chart, an H speed rated tire has been tested up to 130MPH

• Q Up to 100mph
• R Up to 106mph
• S Up to 112mph
• T Up to 118mph
• U Up to 124mph
• H Up to 130mph
• V Up to 149mph
• W Up to 168mph
• Y Up to 186mph
• Z 149mph and over

Typically the higher the speed rating, the better performance the tire. Many of your sporty sedans have V rated tires on them and all of your sports cars have W,Y, or Z Rated tires.

DOT Quality Grades or UTQG:

Some manufactures call this a DOT Quality Grade, some call it a UTQG or Uniform Tire Quality Grade. This grade is an indicator of tread wear, traction, and temperature.

Our Uniroyal has a DOT Quality Grade of 460 A A

 

Tread wear 460: NOTE ON TREAD WEAR RATINGS.. THEY ARE NOT UNIFORM

 

This is what I mean: a 460 tread wear Uniroyal IS NOT the same tread wear as a 460 Goodyear, which IS NOT the same as a 460 Cooper.

 

 A tread wear is only comparable within a certain brand or a family of brands. Tread wear ratings are determined like this:

 

Goodyear tests a baseline tire and lets say this tire gets 40,000 miles of tread wear. Goodyear then will assign this tire a tread wear rating of 340 for argument sake.. They test another tire and it gets 80,000 miles. This tire will be assigned a 680 tread wear because it got twice the mileage of the baseline, thus getting a rating twice that of the baseline.

 

With that said, most manufacturers are a pretty close correlation between tread wear ratings and actual mileage. 

 

As a general rule of thumb, and a quick and dirty way to guesstimate tread life: For every 100 of tread wear rating you get 10k - 12k miles. I.E a tire with a tread wear of 320 can be guessed to be about a 35,000 mile tire

 

Traction: Traction ratings indicate the ability to stop from strait line movement on wet pavement. This rating is either AA, A, B, and C, AA being the best rating. Typically the higher performance the tire, the better the traction rating.

 

Temperature: Is the ability to dissipate heat. This rating is either an A, B, or C. A being the best rating. 

PLY/Load Range:

A Ply or Load range is found on tires for heavier vehicles. 3/4 and 1 ton trucks, vans and SUV require tires that are usually 10 ply or Load Range E. These tires will have an LT before the size, and a load range on the sidewall

 

Load Ranges and corresponding Ply Ratings:

 

Load Range C = 6 Ply

Load Range D = 8 ply

Load Range E = 10 ply

Load Range F = 12 ply

PLY / LOAD RATING MYTH:  

It is very common for owners of heavy trucks i.e Ford F250/350, Chevrolet/GMC 2500-3500 to move up in size from stock.

 

Let use a 2006 Chevrolet 2500 for example. Stock size was a LT245/75R16 10 Ply (Load Range E) The load index, as discussed above is a 121 or 3297 lbs per tire.

 

The owner wants to upgrade to a LT285/75R16, but the tire he wants only comes in an 8 ply, so the assumption is that it will not work on his truck. NOT TRUE.

The larger the tire, the lower the ply required to maintain the same load rating. A LT285/75R16 Falken Wild Peak A/T in an 8 ply has a load index of 122 or 3307 lbs per tire

The 8 ply is plenty heavy enough for his use and a 10 ply is NOT REQUIRED

A note/warning about this: Many of the newer vehicles come with tire pressure monitoring systems  or TPMS. The TPMS requires a certain air pressure to be maintained. The 8 ply tire has a lower maximum air pressure than the 10 ply. Without changing TPMS sensors, your tire pressure light may come on indicating low air pressure. This however has nothing to do with the tire's ability to carry your load.

 

Thank you for reading this blog entry. I hope that it was informative. Should you have any questions, please do not hesitate to contact us. And thank you for supporting OnlineTireDeals.com