Old Tire Size Conversion – A Complete Guide

Last Updated on 8月 15, 2019 by Carusedjp

Think wiping wax all over your car is enough? Think again! Any car expert would agree that regular maintenance is the life of a vehicle. Old or new, vehicles need to be pampered and checked from roof to tires. Otherwise, you’d jeopardize both your comfort and safety, especially if you don’t pay attention to the little details.

Today, we’d be looking into one very important car part: the tires. Checking tire size and integrity is critical in vehicle maintenance. If the size of your new tires doesn’t match the old ones, the speedometer and the anti-lock braking system may not function optimally. Similarly, irregularities in tire size can also affect the car as a whole since it makes the chassis more vulnerable to bumping into the surface of the road.

With this in mind, it is important that you take a proactive approach in maintaining your vehicle, specifically your tires. To get you started, below are some of the important things you need to know about checking and changing tires.


What is a Tire Size Conversion Chart?

A tires size chart is a tabular presentation that contains information on tire measurements. If, for instance, you need to change the tires of a used or a vintage car, this chart can guide you in choosing the right tire size.

Nonetheless, since tire size is highly dependent on factors like wheel diameter and size, a tires size chart may not display measurements that perfectly match your car’s needs. In cases like this, you’d need to either ask advice from your mechanic or learn how to read tire size.

Size Matters: How to Read Tire Size

All tires were manufactured with a number sequence at the sidewall at the front. The sequence gives you information on the tire size, along with other important details. To demonstrate how to read tire size, let’s assume that P205/55R16 95H is our sequence.

  • Tire Type: In the sequence, letter “P” represents the tire type. While “P” means “passenger,” “LT” means “light trucks.” Between the two, “LT” tires need higher inflation pressure.  
  • Tire Width: The 3 numbers that follow the letter pertains to the width of the tire in millimeters. In our sequence, the tire’s width is 205 mm.
  • Tire Aspect Ratio: The 2 digits after the slash represent the tire aspect ratio, which describes the relationship between the tire’s cross-section height with its width. In the sequence, for instance, 55 means that the tire height is around 55% of the width. As the tire aspect ratio increases, the sidewall of the tire also grows bigger.
  • Tire Construction: In the sequence, letter “R,” which is written after the tire aspect ratio, refers to the construction of the tire. Here, letter “R” means radial, which indicates that the speed rating of the tire is lower than 150 mph. Vehicles exceeding 150 mph carry the letters “ZR”.
  • Rim Diameter: The next two digits pertain to the rim diameter the tire is designed for. In the example, the tire can fit a 16-millimeter rim.
  • Load Index: This refers to the maximum load capacity of the tire once it is fully inflated. In the sequence, “95” is the load index of the tire.
  • Speed Rating: The last letter in the sequence represents the tire’s speed rating, which gives drivers an idea on the maximum speed capability of the the tires.

By learning how to read the tire size, you can easily decide whether a tire best fits your vehicle or not. If you’re still confused on how to find the ideal tire, pay a visit to your mechanic. After all, you’re always better safe than sorry.

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