Though performance plays an important role in deciding a vehicle, auto enthusiasts do give a lot of importance to aesthetics. They are eager to provide their vehicles with a muscular look, which often leads to modifications and customization. One common customization technique is Tyre Upsizing. A vehicle’s tyres have a direct impact on its performance, design and handling. Tyre upsizing gives vehicles a charismatic stance. However, it comes with its set of disadvantages if not done with care. Before looking in detail at the factors to consider while upsizing, let us look at both the pros and cons of this technique.

Pros

Aesthetics: As mentioned above, tyres have a direct impact on the overall aesthetics of the vehicle, especially in utility vehicles. They improve the overall sturdiness of the vehicle.

Handling: Increasing the tyre size, in turn, increases the width of the thread. This improves cornering and handling as the side walls are now made stiffer.

Braking: Upgrading the size translates to more rubber. This provides a better contact patch, which in turn improves the overall braking system.

Cons

Cost: The bigger the tyre, the higher the expense. Top-end cars come with a bigger rim size. Upsizing the tyres of these cars requires a lot of technical expertise and hence finding the right size becomes expensive.

Performance: Increasing the size of the tyre adds more weight to the vehicle. When the tyres get heavier, there is an increase in the strain taken by the engine. This directly affects both the mileage and acceleration of the vehicle.

Suspension System: The default suspension system of a vehicle is designed based on the vehicle’s original specifications. Increasing the tyre size strains the suspension system and causes easy wear and tear.

Faulty Speedometer: Speedometers are calibrated for a particular tyre size. If 18-inch wheels are upgraded to 20-inch wheels, the reading will not be accurate. The increase in the diameter will result in faulty readings.

Considering the above factors, should one choose to upsize or not?

Absolutely! From a vehicle’s aesthetic point of view, one can be compelled to go with upsizing. However, vehicle owners must exercise utmost care before upsizing. It is recommended to consult a professional’s advice before choosing the right tyres for your vehicle.

Before looking at the factors that influence tyre upsizing, let us first look at the various upsizing techniques.

1. The Plus Zero Method: In this method, the new tyre has a larger section width with a smaller aspect ratio than the factory-fitted tyre. However, the diameter of the tyre remains the same.

2. The Plus One Method: In this method, there is an increase of one inch in the overall diameter with a lower aspect ratio than the factory-fitted tyre.

3. The Plus Two Method: If there is an increase of two inches in the overall diameter with a lower aspect ratio, you are using the plus two method.

Tyre Upsize Calculation:

One major misconception regarding tyre upsizing is that it is possible to bring a major change in the diameter of the tyre. The truth however is that there is limited scope to increase the diameter of the OEM tyre.

The total diameter is the sum of the wheel (or rim) diameter and the Sidewall. For a safe upsizing, the total diameter should not be increased more than 3%.

Let us consider an example of a Honda City with a R15 175/65 tyre. Let us check if it would be ideal to change it to R16 185/55 tyres or if R15 195/60 tyres would suit better.

Diameter of the existing tyre = Size of the tyre (15 * 2.54 cm) + Sidewall width of both sides (17.5 * 0.65 * 2) = 60.85 cm

Diameter using R16 185/55 tyres = Size of the tyre (16 * 2.54 cm) + Sidewall width of both sides (18.5 * 0.55 * 2) = 60.99

Diameter using R15 195/60 tyres = Size of the tyre (15 * 2.54 cm) + Sidewall width of both sides (19.5 * 0.60 * 2) = 61.5

Based on the above calculations, the ideal choice would be to use R15 195/60 tyres since the difference falls within the 3% range. This eliminates the need to change the wheels as they are of similar size. The height of the tyre is also not reduced considerably.

Other factors to consider while upsizing tyres

Free movement: The most important factor to be considered during tyre upsizing is to ensure that the tyres are not making any contact with the body of the car. Cars are designed to be compatible with certain tyre sizes and increasing these limits can cause the tyres to rub against the body of the car.

Holding capacity: It is important to ensure that the new tyre’s load-bearing capacity is greater than or equal to that of the factory-fitted tyres. Loading cars over its holding capacity can cause the tyres to burst leading to accidents.

Recalibrating the speedometer: Since the speedometer is calibrated to account for the circumference of the tyre, it is important to accurately calibrate it after upsizing.

Proportional sidewall and width: If one chooses to go with a tyre with a larger width, the sidewalls should be proportionally decreased. Similarly, if one chooses a high profile tyre, then the width of the tyre should be decreased.

Impact on suspension system: As mentioned at the beginning of this article, upsizing has adverse effects on the suspension of the vehicle. Every car’s suspension system is designed to take a maximum load limit and increasing the weight of the car beyond the limit can lead to a lot of performance issues. Low profile tyres are softer in nature and are hence bad for the suspension of the vehicle.

There are quite a few things to consider before going in for tyre upsizing. The best way is to get experts to do it under professional guidance, so you can experience all the advantages both functionally and aesthetically.