Tire Comparison Calculator

Updated Jun 25, 2026 By Jehan Wadia

Introduction

Changing your tire size affects more than just how your vehicle looks. A different tire can change your speedometer reading, ride height, and how your car handles on the road. Before you buy new tires, you need to know exactly how they compare to your current ones.

This tire comparison calculator lets you enter two tire sizes and see all the key differences side by side. It calculates overall diameter, sidewall height, section width, circumference, and revolutions per mile for both tires. It also shows you how much your speedometer will be off if you switch to a different size. You can view a visual comparison, follow the step-by-step math, and browse alternate tire sizes that are close in diameter to the size you want.

Just enter your current tire size and the new tire size you are thinking about. If you don't know your stock tire size, use the built-in vehicle lookup tool to find it by year, make, and model. Hit Compare Tires and get your results in seconds.

How to Use Our Tire Comparison Calculator

Enter your current tire size and the new tire size you want to try. The calculator will show you the differences in diameter, width, sidewall height, and speedometer accuracy between the two tires.

Current Tire Width: Type the section width of your current tire in millimeters. This is the first number in your tire size code, like 265 in 265/70R17.

Current Tire Aspect Ratio: Type the aspect ratio of your current tire. This is the middle number in your tire size code, like 70 in 265/70R17. It tells you the sidewall height as a percent of the width.

Current Tire Rim Diameter: Type the rim size of your current tire in inches. This is the last number in your tire size code, like 17 in 265/70R17.

New Tire Width: Type the section width of the new tire you want to compare, in millimeters.

New Tire Aspect Ratio: Type the aspect ratio of the new tire you want to compare.

New Tire Rim Diameter: Type the rim size of the new tire in inches.

Vehicle Lookup (optional): If you do not know your current tire size, click the lookup button. Pick your vehicle's year, make, and model, and the tool will fill in your factory tire size for you.

Unit Toggle: Use the inches/millimeters switch above the results table to change which unit of measurement shows first.

Press Compare Tires to see your results. Press Reset to clear all fields and start over.

What Is a Tire Size Comparison?

A tire size comparison shows you how two different tires stack up against each other. Every tire has three numbers in its size code, like 265/70R17. The first number is the width of the tire in millimeters. The second number is the aspect ratio, which tells you how tall the sidewall is compared to the width. The last number is the rim diameter in inches. When you change any of these numbers, it affects the overall height, width, and shape of your tire. If you need to convert a single tire size into actual dimensions, our tire size calculator can help with that.

Why Tire Size Matters

Switching to a different tire size changes more than just how your vehicle looks. A larger tire covers more ground per rotation, which means your speedometer will read lower than your actual speed. A smaller tire does the opposite. You can use a speed calculator to better understand the relationship between distance, time, and velocity. This also affects your odometer, fuel economy, and how your vehicle handles. Most experts recommend staying within 3% of your original tire diameter to avoid problems with your vehicle's systems.

How to Read a Tire Size

Look at the side of your tire. You will see a code like 225/65R17. Here is what each part means:

225 — Section width in millimeters (how wide the tire is)
65 — Aspect ratio (sidewall height is 65% of the width)
R — Radial construction (the most common tire type)
17 — Rim diameter in inches

When to Compare Tire Sizes

You should compare tire sizes before upgrading to bigger wheels, fitting off-road tires, or replacing your stock tires with a different size. If you are moving to a larger or smaller wheel, use a wheel offset calculator alongside this tool to make sure the new setup fits your vehicle without rubbing. You should also check your bolt circle to confirm the new wheels match your hub pattern. Comparing first helps you avoid rubbing against fenders, incorrect speedometer readings, and potential safety issues. If you are unsure of your current tire size, check your driver-side door jamb sticker or your owner's manual for the factory-recommended size. Once you have settled on new tires, you may also want to explore fuel cost differences or estimate monthly payments with an auto loan calculator if you are financing wheels and tires together.

Formulas used

Sidewall Height

H = \frac{A}{100} \times W

Overall Diameter

D = (R \times 25.4) + 2 \times H

Circumference

C = \pi \times D

Revolutions per Mile

N_{\text{mile}} = \frac{5280 \times 12 \times 25.4}{C}

Revolutions per Kilometer

N_{\text{km}} = \frac{1{,}000{,}000}{C}

Actual Speed (Speedometer Correction)

V_{\text{actual}} = V_{\text{indicated}} \times \frac{C_{\text{new}}}{C_{\text{old}}}

Frequently asked questions

What does the difference in tire diameter mean for my car?

A bigger diameter means your tire is taller. This raises your ride height and makes your speedometer read slower than your real speed. A smaller diameter does the opposite. Most mechanics say you should stay within 3% of your original tire diameter to keep everything working right.

How does tire width affect driving?

A wider tire puts more rubber on the road. This can give you better grip when turning and braking. But wider tires can also rub against your fenders, lower your fuel economy, and make your steering feel heavier. A narrower tire does better in snow and uses less fuel.

What are revolutions per mile and why do they matter?

Revolutions per mile tells you how many times your tire spins to travel one mile. A bigger tire spins fewer times, and a smaller tire spins more. Your car's computer uses this spin count to figure out your speed and distance. If the count changes a lot, your speedometer and odometer will be off.

Can I put a different rim size on my car?

Yes, but you need to adjust the tire's width and aspect ratio so the overall diameter stays close to stock. This is called plus-sizing. For example, going from a 17-inch rim to an 18-inch rim means you need a shorter sidewall. The alternate sizes section of this calculator shows you options that keep the diameter similar.

What is sidewall height and why does it matter?

Sidewall height is the distance from the rim to the outer edge of the tire. A taller sidewall absorbs more bumps and gives a smoother ride. A shorter sidewall gives sharper handling and a sportier feel but makes the ride rougher. This calculator finds sidewall height by multiplying the width by the aspect ratio.

How accurate is the speedometer discrepancy table?

The speedometer table is based on math that compares the circumference of both tires. It assumes your speedometer is perfectly calibrated to your current tire. In the real world, factory speedometers can already be off by 1–2%, so treat these numbers as close estimates.

What does the aspect ratio number mean?

The aspect ratio is the middle number in your tire size code. It tells you the sidewall height as a percentage of the tire's width. For example, an aspect ratio of 70 on a 265 mm wide tire means the sidewall is 70% of 265, which is 185.5 mm tall.

Will bigger tires hurt my gas mileage?

Usually, yes. Bigger and wider tires are heavier and create more rolling resistance. This makes your engine work harder, which uses more fuel. The difference is usually small, but it adds up over time. Taller tires can also change your gear ratio, which affects efficiency.

What does the alternate sizes section show me?

It shows tire sizes that have a similar overall diameter to your new tire. These are options you could use instead. Each one is within 1.5% of your chosen tire's diameter. You can click any alternate size to load it into the calculator and compare it right away.

Can I compare tires with different rim sizes?

Yes. You can enter any rim size between 10 and 30 inches for each tire. The calculator will figure out the overall diameter for both and show you exactly how they differ. This is useful when you want to move to bigger or smaller wheels.

How do I find my current tire size?

Look at the sidewall of your tire. You will see a code like 225/65R17 printed on it. You can also check the sticker on the inside of your driver-side door or look in your owner's manual. If you still cannot find it, use the vehicle lookup tool at the top of this calculator to search by year, make, and model.

What do the colors in the results table mean?

Green cells mean the new tire is larger or faster in that category. Blue cells mean the new tire is smaller. Orange cells in the speedometer table mean your actual speed is slower than what the speedometer shows. Gray means there is little to no difference between the two tires.

Is it safe to switch to a much bigger tire?

Going too big can cause problems. Large tires may rub against your fenders or suspension parts when you turn or hit a bump. They can also throw off your anti-lock brakes, traction control, and stability systems. Stay within 3% of your original diameter unless you plan to modify your vehicle.

What is tire circumference used for?

Circumference is the distance around the outside of your tire. It determines how far your car moves with each tire rotation. Your vehicle uses this distance to calculate speed, mileage, and shift points. A bigger circumference means you travel farther per rotation.

What is the difference between the side-by-side, profile, and overlay views?

Side-by-side shows both tires next to each other with width and sidewall info. Profile shows them next to each other with circumference and revolutions per mile. Overlay puts one tire on top of the other so you can see the exact size difference. All three views are drawn to scale.