How to: Calculating Tyre Size for Upsizing

by Tyres S. car tyres in Shrewsbury

There is a fair chance that you must have heard a lot about upsizing and have made up your mind to get it done. Here is a brief of everything that you need to know. In the tyre upsizing process, the original tyre is replaced by a larger tyre and a low profile one is fixed. However, not many changes are made to the diameter and circumference to prevent any drastic changes in the performance. Before upsizing, you need to understand the terms related to the tyre and calculate the right size of the same. Let's see how.

Basics of Calculation

To find the right side of the tyre, you first need to understand all the basic terms. So, the size of the tyre is mentioned on the sidewall. It is represented using numbers and letters. The terms are:

Tyre width
Aspect ratio
Tyre construction
Rim size
Load capacity or index
Speed rating

For example, consider a tyre size 210/50R15/90V. Let’s see how to interpret it.

The first three numbers, i.e. 210 stands for width in mm (millimetres). 50 specifies the aspect profile. The aspect ratio is the height difference from tread to the rim and is mentioned in percentage. Here 50 implies that the tyre height is 50% of its width.
The letter R represents the Radial ply type tyre construction. The next two digits indicate the rim diameter in inches. In this case, the diameter is 15 inches. Please note that 15 inch is the rim diameter and not the tyre diameter.
Next, the digits 90 represent the load index of the tyre. You can check the maximum load on the tyre per lbs using a car tyre load index rating table. For an index of 90, the max load for the tyre is 600 lbs.
The letter V also stands for a code that shows the maximum speed at which a tyre can be used and is called speed rating. For tyres having the speed rating V, it can operate at a speed of up to 240 miles/h.

Mathematics: Calculating Formula

You can use various calculators accessible on the internet for this purpose. You will need to input the data such as the original tyre and upsizing the tyre’s width, aspect ratio, and rim size. The results will show you the difference in the circumference in mm as well as %.

Other than this, you can also try manual estimations. For this, you only need the rim diameter. In the above example, the rim diameter is 15 inches. So, you need to find the total diameter of the tyre. The formula is as follows:

Width in cm+ (aspect ratio % × Width in cm) + (rim diameter in inch × 2.54)

Here, 2.54= 1 inch

So,

21+ (50% of 21) +15×2.54=49.04

Now, perform the same calculation for the tyres Ludlow that you are looking forward to purchase for upsizing. The difference between both should not surpass 3%. If the difference increases by 3%, then you may experience unfavourable changes such as reduced fuel efficiency and difficulty in handling the car.

After calculating the right tyre size, always remember that you will also have a speedometer & odometer error. This means once the upsizing is done, you need to re-calibrate the scales. The speedometer will usually over-read after upgradation and the value depends on the new tyres Berrington. Moreover, it is always recommended to get the tyre sizes examined by experts. Your calculation may or may not be very precise, so getting professional help will be beneficial.