Car tyre size is a very important factor to consider if you are planning to upgrade or change your car tyres. It keeps your car safe and improves overall performance. With increasing automobile sales. The number of car owners who are planning to upgrade or change their car tyre is also increasing.
Thankfully finding the right wheel size is fairly simple. All the information required is available in the owners manual or somewhere in the car itself. The physical measurements like diameter and width of car tyre are some of the factors behind finding the car tyre size.
There are some additional details you should consider like load index and speed rating are also crucial to finding the car tyre size.
Where to find Car Tyre Size?
No matter which car model you own. You will always get car tyre size written on the owners manual. If by Chance the manual is not available with you. You can also find the tyre size in these locations.
- The driver’s side doorjamb
- Inside your glove box compartment
- Within your oil tank hatch
Assuming that your car already has original company fitted tyres. no matters where you are getting the car tyre size you always have to decode the letters written on the car tyre to know the size.
How to read car tyre size?
Let us take a look at each number or letter one by one. In order, they are written on the tyre. we will be using a tyre size as an example: 165/55R17 94H
Here 165 is the width of the tyre in MM, 55 stands for aspect ratio, The letter R stands for Radial (Radial construction). The Number 17 stands for internal diameter it is also called RIM size. the number 94 is the load index which determines how much load each tyre can carry.
The last letter H is tyre speed symbol marking. you can also consider it as maximum vehicle speed.
Meaning of The Letters P and LT
For most vehicles, you’ll see the letter “P” before the number sequence begins: P225/70R16 91S. The “P” is short for “P-metric” which is a designation by the Tyre and Rim Association for a “passenger car” tyre type.
This signifies the tyre was designed to primarily be used on passenger vehicles, which can include cars, minivans, SUV’s, and other light-duty pickup trucks.
If you see “LT” instead of “P,” it’s because you need “light truck” tyres – “LT” is short for “LT-metric” which is a designation by the Tyre and Rim Association for a “light truck” type tyre.
Light truck tyres are designed to be used on vehicles capable of carrying heavy cargo or pulling trailers. Similarly, “T” stands for “temporary” and is for your spare tyre. If you see “ST,” that means “special trailer.”
The first number to appear in your tyre size information is the width, in millimetres, of the correct tyres for your vehicle: 165/55R17 94H
Tyre width always refers to the measurement from one sidewall to another. Thus, a tyre with the measurement “165” is for a passenger vehicle and has a nominal width of 165 millimetres.
Car Tyre Aspect Ratio
After the slash mark, the next number you see is for the tyre’s aspect ratio, which essentially tells you how tall your tyre’s profile is: 165/55R17 94H. Aspect ratios are delivered in percentages. Tyre makers calculate the aspect ratio by dividing a tyre’s height off the rim by its width.
If a tyre has an aspect ratio55, it means the tyre’s height is 55% of its width. Lower aspect ratio tyres, such as a 45 series, generally offer vehicle handling performance advantages over higher aspect ratio tyres, such as a 55 series.
After the aspect ratio comes a letter that indicates the type of internal construction maintaining your tyre’s stability: 165/55R17 94H. There are two types of construction that you may see on the sidewall of a tyre:
- R – Radial
- D – Diagonal or Bias Ply
Radial construction means the tyre’s internal ply cords are oriented in a radial direction, from one bead over to the other, essentially perpendicular to the axis of rotation.
Tyre Rim Diameter
The next number is the diameter code, in inches, of the rim on which the tyre can be mounted. For example, a tyre with the 165/55R17 94H would fit a rim with a 17-inch diameter.
The next figure in the sequence is your tyre’s load index, which tells us how much weight, in kilograms, the tyre can support when fully inflated: 225/70/R16 91S
We call it the load “index” because the number doesn’t tell us the precise number of kilograms the tyre can carry, at least not by itself. However, the number does correspond to a specific load capacity listed in an index.
Beginning with 60 and ending with 179, numbers in the load index represent carrying capacities of 250 to 7750 kilograms.
The final figure in a tyre size sequence is the speed rating, which is indicated by a letter: 225/70/R16 91S. Just as your load index number corresponds to a particular load, your speed rating letter corresponds to a particular speed capability based on a standardised laboratory test.
For example, a tyre with a speed rating “S” is rated for up to 180 km/h, while a tyre rated “R” is up to 170 km/h. Remember that this isn’t a recommended cruising speed. Of course, you should always follow legal speed limits on the road.
Tyres with higher speed ratings, tend to offer increasing handling performance. Replacement tyres must have a similar or higher speed rating to maintain vehicle speed capability. If a vehicle has tyres with different speed ratings, it is the speed rating of the “slowest” tyre that dictates the vehicle top speed.
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