Tyre Upsizing

In today's age while making a buying decision we have multiple choices and automobiles are no different. Though factors like price and performance play an important role but looks and aesthetics impact decision making to a large extent especially for automobile enthusiasts. Some of them like to have a sporty and different look for their vehicle.

Mostly vehicles come with regular tyres but many like to upgrade their tyres for reasons mentioned above. While upsizing adds to the appeal, it may also affect its performance significantly. Therefore, Vehicle owners may like to consider a number of factors before upsizing their tyres

Technically, tyre upsizing can be performed in two ways, such as:

  1. Mounting wider tyres while retaining the original wheels
  2. Upgrading to larger wheels and installing wider tyres

Benefits of Tyre Upsizing

Besides a cosmetic uplift in car's profile, tyre upsizing brings the following benefits for owners.

Personalization: For many car owners, tyre upsizing is one of the quickest ways to personalize their vehicle and add oomph to its side profile. In other words, wider tyres make your vehicle look cool, boosting its style quotient.

Greater Stance: Technically, wider tyres offer a larger contact patch generating more grip on the road. This helps the driver maintain greater control and stability, especially when the vehicle is cruising at a relatively higher speed.

Safe Breaking: Larger tyres significantly reduce the breaking distances offering better control while breaking. This also means little or no skid and therefore, more safety.

Easy Cornering: Suspension plays a key role in corning your car. Wider tyres tend to have slimmer sidewall flex which enables the driver to corner better even when the vehicle is moving at high speed.

Overall Control: Tyre upsizing enhances the overall performance of a vehicle with regards to its balance, stability and traction. This can prove to be an asset for vehicles that have understeering or oversteering nature since wider tyres help the driver balance the vehicle properly, making driving safe and secure.

Disadvantages of Tyre Upsizing

Despite the aforementioned benefits, tyre upsizing also has a few significant drawbacks that discourage many car owners.

Higher Cost: Tyre upsizing can be an expensive proposition for some, depending on factors such as the type of vehicle and tyres used. However, in general, larger wheels and tyres mean more expenses for the car owner.

Reduced Acceleration: While large wheels and wider tyres mean a great grip on the road, they can cost vehicle's performance in terms of affecting its acceleration. Wider tyres add to the overall body weight of the vehicle thereby increasing burden on the engine capacity and slowing down its acceleration.

Weighted Steering: With a larger contact patch, wider tyres and large wheels improve stability. However, at the same time, they mean a heavy steering, which requires more effort from the driver to manoeuvre and control the steering. This can cause a significant disadvantage to drivers who prefer to drive vehicles with a light steering, and in a slow traffic scenario.

Low Fuel Efficiency: Tyre upsizing can also affect the fuel efficiency of a vehicle. With wider tyres and larger wheels, the car has a better grip on the road, which affects the rolling resistance negatively. As a result, the car will need more revs to move efficiently, consuming more fuel in the process.

Wrong Speedometer Reading: Done incorrectly, tyre upsizing can affect the reading in your vehicle's speedometer. Car owners must exercise care in choosing the right tyre for upsizing. Tyre experts recommend upsizing tyres proportionately; meaning the increase in width of tyres should be equally proportionate to the decrease in tyre's sidewalls. If the diameter of upsized tyres goes higher than that of the original tyres, it may affect reading of the speedometer and hamper the performance many other modern systems such as ABS, ETC, ESP and TPMS.

Little Driving Comfort: Tyre upsizing can adversely affect the riding quality. With larger wheels and wider tyres, the length of the sidewalls goes drastically down, leaving little or no sidewall flex for the wheels to absorb shock on bumpy roads. Hence, this makes riding less comfortable for the driver and passengers alike.

So, Should one upsize or not?

While tyre upsizing is a compelling proposition from the standpoint of a vehicle's aesthetic appeal, vehicle owners must factor in a number of aspects related to their regular driving requirements. Moreover, it is highly recommended that vehicle owners consult professional tyre experts in order to determine if tyre upsizing is a wide move for them.

How to Calculate Tyre Upsizing

Tyre upsizing calculations are key to achieving optimal performance for your vehicle. There are two ways go about it.

Retaining Original Wheels/Alloys:

For safe upsize, you must ensure the OD (overall diameter) of the new tyres remains within the permissible tolerance, which is only up to 3% of the OD of stock tyre.

For example, if the OD of the stock tyre is 24.47 inches, then the OD of the new tyre should not go beyond 25.20 inches.

Here's how to achieve the permissible tolerance.

Tyre Width:

Let's assume the original tyre size is 185/65 R15 with an OD of 24.47 inches.

So, the width of our stock tyre is 185mm.

For safe upsize, let's add 20mm to the width of your stock tyre.

So, the width of your new tire should be 205mm.

Sidewall Height:

The sidewall height of our stock tyre is 65% of the thread width.

As per the thumb rule, for every 10mm increase in width of tyre, the sidewall height (or aspect ratio) should be reduced by 5 percent.

In our example, the sidewall height should be reduced by 10 percent since there was a 20mm increase in the width of our tyre.

So, the sidewall height of the new tyre should be 55% of the thread width.

Rim Size:

The Rim size or diameter should remain the same. In this example, it is 15 inches.

Therefore, the max upsize for a stock tyre size (185/65 R15) should be 205/55 R15.

Upgrading to Larger to Wheels/Alloys

If we want to upgrade to a bigger alloy, we still need to stick to the permissible tolerance mentioned in the previous example.

If we want to upgrade to a 16-inch alloy wheel, then size of the new tyre should be 205/55 R16, keeping the OD within 3% permissible tolerance, i.e., 24.87 inches.