Tyre Upsizing Guide

Tyre Upsizing: A Quick & Complete Guide For Beginners

The tyre upsizing seems like a buzz word but it is not. Simply put, when you upgrade your current set of wheels either by putting wider tyre or bigger wheel, it is known as upsizing. Though it looks easy when you actually go down to do the upsizing you need to take care of a number of factors. As any change in the tyre is directly linked to your safety and performance of your vehicle.

Types of tyre upsizing

There are two ways by which you can perform the tyre upsizing.

  1. When the wheel or alloy is kept the same and the tyre is replaced by broader or fatter tyres.
  2. When you upgrade the complete wheel or alloy along with its tyres to a bigger set of wheels and wider tyres.

In your efforts of upsizing, you need to be extremely cautious about the overall diameter of the tyre getting affected. Because, if the tyres are not proportionate, it may lead to severe damage to you as well as your vehicle. The overall diameter should not go beyond 3 percent of the company provided wheel size.

Things to know about the overall diameter of a tyre

You need to understand, what is an overall diameter (OD) of a tyre before you proceed for the tyre upsizing task. The overall diameter of a tyre is calculated from the outer surface of the tyre. Any alteration to the diameter has a direct, adverse impact on the vehicle’s gearing, steering response, suspension, handling, odometer reading and lastly its fuel mileage.

The thumb rule for tyre upsizing is, the wider the tyre the smaller is the sidewall so that the balance is maintained between the two. The good thing about upsizing is that it increases the visual appeal of the wheels manifold. However, on the flip side, the shorter sidewall has lower shock absorption capability compared to higher sidewalls. With lesser rubber area to flex, the ride on rough surfaces or uneven turfs becomes uncomfortable due to road bumps filtering directly into the cabin.

 

How to read a tyre

Before you go for upsizing, first you need to know what the figures on your tyre read and mean. You can easily find some alphanumeric text in big fonts on the sidewall of your vehicle’s tyre. Let’s take an example of Maruti Suzuki S-Presso’s tyre which reads 145/80 R 13 75S. Here is what it means.

Full Detail is here  – How To Read A Car Tyre?

 

145 It is the width of the tyre usually measured in millimetres. This is the portion of the tyre which is in contact with the surface.
80 This is the height of the sidewall and is the percentage of the tread width. In this case, it is 80 percent of the tread width. It is also termed as the aspect ratio. In upsizing, the wider tyre should have lower sidewalls to keep proportions of the tyre in check.
R It was meant to denote the radial construction of the tyres. Now, most cars and utility vehicles come with factory-fitted radial tyres.
13 This is the size of the rim and is measured in inches. It is basically the diameter of the wheel on which the tyre is fitted.
75 These numbers are the load index of a tyre that indicate its safe weight carrying capacity.
S The speed rating of the tyre. Mentioned in the alphabet (alphanumeric in some cases) they signify different speeds at which the vehicle can be driven. Here, ‘S’ stands for the highest speed of 180 km/hr with recommended tyre pressure.

 

Let’s dive deep into types of tyre upsizing

Only tyre upsize, no wheel or alloy

If you wish to upsize only the tyre and not the wheel or alloy, the safest option should be to go for a 20 mm rise in width over the currently fitted tyres in your vehicle. For instance, let’s consider a tyre of size 185/65 R 15. A bump of 20 mm would increase its width from 185 mm to 205 mm, which should work just fine with the SUV.

Now, as a thumb rule, the sidewall height should drop by 5 percent for every 10 mm increase in the width. For instance, here we are increasing the width by 20 mm so the percentage of drop would be 10 percent. Hence, in our case, the 65 percent aspect ratio now drops to 55 percent.

As we didn’t tweak the radial construction nor the rim size, rest other details remain the same. The figures of the newly added tyre now read 205/55 R 15.

Going by the equation of not going beyond the 3 percent of the original overall diameter, let’s see how much percent of alteration is done to the original tyre. The new overall diameter now reads 23.88-inch whereas the stock one read 24.47-inch; so the difference between the two is of 2.4 percent – well below the intended 3 percent mark. This makes for a safe upsizing.

Going for bigger wheels/alloys

If you want to upsize the whole wheel or alloy setup, the same rule of 3 percent applies here as well. For instance, you are considering to upsize a tyre of 185/65 R 15 measurement to 16 inches, then going for a wheel with 205/55 R 16 should be the ideal one. As we know the stock overall diameter was 24.47 inch, after calculating the value in inches for the new wheel we reach to a conclusion of 24.87 inches – 0.40-inches more than the stock one. When converting, it comes as 1.6 percent of variation compared to the stock tyre. Falling under the recommended percent of 3, the 205/55 R 16 falls in the safe category of upsizing.

Though it’s a subjective decision to upsize the tyres of your vehicle, they at times become necessary due to manufacturer providing very slim/puny tyres to save costs. Let’s have a look at the benefits one gets post upsizing.

What are the merits of Upsizing?

  1. Increased grip, traction and braking: The instant and most obvious benefit that you get with upsizing is better grip as you get increased contact with the turf due to fatter tyres. Moreover, the increased rubber also offers better traction and better braking.
  2. Spot on cornering: Since the fatter tyres have low sidewalls, the bumpy effect of the vehicle due to tyres is controlled to a great degree, giving you excellent experience while cornering.
  3. Jazzed up looks: The most common reason for upsizing is for the looks and it certainly elevates the appearance of the vehicle.

What are the demerits of Upsizing?

  1. Wet is a deterrent: With wider tyres having bigger contact patches, the tyre may be subjected to hydroplaning unless it is a wet tyre.
  2. Heavier steering: Going for broader tyres means putting the steering to additional stress.
  3. Low Mileage: In most cases, bigger tyres have reported to bring down the fuel efficiency of the vehicle as the same engine has to now drag a heavier vehicle.
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