There is a ton of information branded into the side of a tire and as confusing as it seems, I promise those numbers will all make sense when we are done.
The numbers designate the type of tire, size, usage, and speed rating if applicable.What do all those numbers on the side of a tire mean?
The first letter indicates the tire’s usage. For example P means Passenger, L T means light truck, T means temporary spare. That wasn’t too bad was it? By the way, if there isn’t any letter, it means a passenger car tire with a couple of small changes. Also passenger car tires also apply to mini vans, small trucks, and small SUV’s.
The next three numbers indicate the width of the tire. This is determined after the tire is mounted and measured from the outermost edge to the innermost edge. A 225 tire is 225 millimeters across. The technical term for this measurement is ‘section width.’
Okay. Take a deep breath and grab a fresh cup of coffee because here is where we put some tape on our glasses.
The next two numbers indicate the tire’s profile or aspect ratio. For example a 50 indicates that the tire’s sidewall height, the distance between the edge of the rim to the tread, is 50% of the section width. Remember the section width from the previous paragraph? Okay let’s put together what we have learned so far. A P225/50 is a passenger car tire with a width of 225 millimeters from the outer edge to the inner edge and the height of the tire, the distance between the outer edge of the wheel to the tread is 50% of the width. Phew! Let’s do one more. An LT245/75 is a light truck tire that is 245 millimeters from edge to edge wide and the distance between the outer edge of the wheel to the tread is 75% of the width.
The next character is an R which stands for radial, meaning the plies of the tire ‘radiate’ from the center of the wheel. There are two other types. B which stands for belted and D which is for bias ply but these types have gone the way of the dodo bird and need no discussion. If you see an F after the R there is a bladder inside the tire that allows the tire to be used on a limited basis with out air. These tires are called ‘Run Flats’ and are standard equipment on high performance cars such as the Corvette. Some of the older model tires do not use the ‘F’ but the later ones do.
The next two numbers indicate the diameter of the wheel and tire and are expressed in inches. If we go back to our 225/60/R example and add the number 16 we have a passenger car tire that has a section width of 225 millimeters, and the distance between the wheel and the tread is 50% of the width and the diameter of the wheel and tire is 16′. Our LT245/75T16 comes out to be a light truck tire that has a width of 245 millimeters, a side with (from wheel to tread) of 75%, and a 16′ diameter tire for a 16′ diameter wheel. Some of the bigger trucks use 17.5 or 19.5 diameter and it means what it says. A 17.5 diameter is 17 ½ inch and a 19.5 is a 19 ½ inch wheel.
The last characters indicate the load index (what the tire is designed to carry) and the speed rating. The higher the number or letter the higher the load capacity and/ or speed. However if a tire has a ‘Z’ speed rating, it is included in the tire size after the construction. i.e. ZR.
The following are a couple of charts which explain load range and speed rating.
Load Rang Index
89 = 1,279 pounds
88 = 1,235 pounds
87 = 1,201 pounds
86 = 1,168 pounds
85 = 1,135 pounds etc.
Speed ratings
L 75 mph 120 km/h
M 81 mph 130 km/h
N 87 mph 140km/h
P 93 mph 150 km/h
Q 99 mph 160 km/h
R 106 mph 170 km/h
S 112 mph 180 km/h
T 118 mph 190 km/h
U 124 mph 200 km/h
H 130 mph 210 km/h
V 149 mph 240 km/h
Now let’s put it all together.
The tire we are going to be working on is a P225/50R16 91S
Okay here we go.
We have a passenger tire with a section width of 225 millimeters and a side profile which is 50% of the width. The tire has a radial construction and fits a 16′ diameter wheel. The load index is 1356 lbs and the speed rating is for 112 MPH.
Now wasn’t that easy?
To find the best place to purchase tires, please visit SAW Automotive Parts Network..
Steve Wagner
Steve Wagner has been in the automobile business as a parts manager for over 40 years and is presently retired living in Florida.
Where can i pump air into my bike tires for free in philadelphia?
I don’t own an air pump and was wondering if this can be done for free anywhere in philadelphia? Preferably west philadelphia or center city area?
Both types? I guess I would get a pump, but im unsure what the both types refers to
Answer
Go buy a bicycle pump, every one that owns a bicycle should have one. There are two different valve types, shrader valves are found on cars and presta valves are more common on thin tired bikes like road and hybrids. The time spend going to a gas station will cost more then the pump itself. You should have a patch kit and a spare tube handy also.
http://bicycletutor.com/presta-valve/
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