Like most car owners and enthusiasts, you’ve probably thought of swapping out your tires for a bigger or smaller set.
The question is, how much difference in tire size is acceptable? Well, experts recommend staying within a three percent range of the original tire size.
Contrary to what many believe, bigger isn’t always better. So even though bigger tires offer higher road clearance and look cooler, they also affect the car’s handling and ride comfort.
This article delves deeper into acceptable tire sizes and the consequences of going over the limit.
What Is an Acceptable Difference in Tire Sizes?
The acceptable tire size difference depends on the type of car you have. For passenger cars – any vehicle designed for the carriage of passengers – the general rule of thumb is to stick within 3% of the size of the current tires.
But for SUVs and pick-up trucks, you can upsize by up to 15% of the initial tire size.
So how can one establish the particular tire sizes that fall within this threshold? The first thing you need to do is figure out the size of your current wheels.
Generally, tire measurements are printed on their sidewalls. So this shouldn’t be too hard to find. What might be tricky is knowing how to read the printed text. Here’s a quick guide to help you decipher the code:
- Type – the first part of this code is a letter(s) describing the intended use of the vehicle. The letters you’ll typically find are:
- P for passenger car
- LT for light truck
- ST for special trailer
- T for temporary; used to describe spare tires
- Tire width – following the letter is a 2- or 3-digit number. This refers to the tire width, which is measured from one sidewall to the other.
- Aspect ratio – the aspect ratio is the number that appears after the forward-slash symbol. It’s a measurement of the tire’s height relative to its width.
- Internal construction – this next part will have one of these three letters: B, D, or R. It describes the interior construction of a tire as follows:
- R – referring to a radial construction. This means the cords inside the tire run along its circumference, just perpendicular to the axis of rotation.
- D – referring to a diagonal construction. Here, the cords also run along the tire’s circumference. However, they’re positioned at 30° to 40° from the bead (the point of the tire that comes into contact with the rim).
- B – used to refer to bias-belted tires. It’s a type of construction that entails adding an extra layer above the uppermost ply layer of the tire.
- Wheel diameter – measured in inches, this figure indicates the tire diameter as estimated from the road’s surface to the topmost part of the wheel.
- Load index – another metric you’ll find in the tire measurement is the load index. It determines the amount of weight that can be supported by the tire at a particular inflation level.
- Speed rating – the last part of the code is the speed rating. It’s a measure of the tire’s highest speed capability that aligns with its load index.
Although the tire measurement will consist of different letters and digits, the main parts you should pay attention to are the tire width and diameter.
Once you’ve identified this, use a tire size calculator such as this one, to determine the extent to which you can upsize or downsize.
Is It Okay to Put Slightly Bigger Tires?
Yes, it’s okay to put slightly bigger tires in your vehicle. But as advised earlier, don’t exceed the 3% range of the original tire size.
Here are some of the perks you stand to gain from installing bigger tires:
- Improved aesthetics – the number one reason why people like replacing tires with bigger ones is to give their car a sportier look.
- Better traction – aesthetics aside, using larger tires also improves your car’s traction. Here’s the thing, a wider tire has a bigger contact patch with the road’s surface. And this improves the grip or traction.
- Easier cornering – a bigger tire has a wider thread and stiffer sidewall. All of these traits improve your car’s cornering ability.
Effects Of Changing Tire Size
Despite the benefits, bigger wheels aren’t always better.
As you’ll see below, changing tire sizes affects multiple aspects; from the fuel efficiency to the suspension, ABS, and more.
When you change tire size, your car’s fuel economy is affected in two ways: rolling resistance and engine efficiency.
Rolling resistance is the ability of a particular tire to resist rolling. If the rolling resistance is high, your car will consume more gasoline to keep moving.
So, it’s important that you change to the right tire size.
Using overly big tires increases the rolling resistance; hence, compromising your car’s fuel efficiency. On the other hand, switching to smaller tires decreases the rolling resistance, making your vehicle more fuel efficient.
The same principle applies when it comes to engine efficiency. Bigger tires force your engine to work harder, increasing your car’s fuel consumption.
Ride Comfort and Braking Distance
If you’re contemplating buying new tires, know that altering their size also impacts the car’s performance. Specifically, it affects the quality of the ride and braking distance.
With regards to braking, bigger tires enable the car to stop faster. Conversely, small tires mean the car travels a longer distance before stopping.
This principle holds true even in ride comfort.
Bigger tires have better shock absorption capability, which makes for a smoother ride. However, small tires are less efficient at this, leading to a bumpier ride.
A lesser-known fact is the impact of tire sizes on a car’s safety features.
Here’s the deal, putting tires that are either too small or too big for your car elevates the risk of a tire failure, especially a blowout. This can occur if the new tires aren’t capable of supporting the car’s weight.
Still on safety, using different tire sizes affects how the suspension and braking systems work jointly.
If the newly-installed tires aren’t compatible with your car’s suspension or brakes, this can lead to premature tire wear and less responsive brakes.
What to Consider When Selecting a Tire Size?
There are a few points you should consider when choosing the new tire size. These are:
First, think about how you plan to use the vehicle after installing the new tires.
For example, if you want to go for off-road adventures, then upgrading to reasonably bigger tires will serve you better.
But, if you’ll only drive the car when running minor shopping errands, switching to smaller tires can help you conserve fuel.
This is one factor that deserves utmost attention. That’s because buying new tires that are too small or too big in circumference affects the car’s handling significantly.
It changes the vehicle’s gearing, speedometer reading, safety systems, and underground clearance. And this means the wheels might start rubbing on the body of the car.
Tire width is another crucial factor to consider. If you buy overly wide tires, there’s a good chance that they won’t fit within your car’s wheel wells.
And when you try turning, the wheels will rub on the suspension components.
Dangers From Selecting Unacceptable Tire Size
Based on the information provided above, it’s important to choose the correct size of tires. Failing to do this will not only affect the car’s handling but also the quality of your ride and your safety.
In fact, installing tires that are too big can affect the function of safety systems, such as anti-lock brakes.
Usually shortened to ABS, the anti-lock brakes restore traction to the wheels in emergency situations; hence, preventing your car from sliding uncontrollably.
Can You Go From 265 to 275 Tires?
Yes, you can. It’s safe to change from a 265 to a 275 tire size as it’s not too far off from the 3% threshold mentioned earlier.
Here’s the exact calculation: (275 mm -265 mm = 10 mm) 10mm/265mm * 100 = 3.77%
Can I Use 65 Instead of 70 Tires?
Yes, you can. If you’re wondering whether it’s okay to swap your 70-sized tires with a 65, the answer is yes.
However, keep in mind that this will change the car’s performance slightly.
The 70-sized tires have a higher sidewall and a bigger overall diameter, which translates to a smoother ride. Meanwhile, the 65 tires have a wider contact patch that improves their traction on paved surfaces.
If you’ve been wondering how much difference in tire size is acceptable, the answer is 3%. Put simply; you shouldn’t choose tires that are not within the 3% size threshold of your original tires.
Doing so can lead to adverse effects, such as tire blowouts, compromised braking and suspension systems, and poor gas mileage.