Tire Size Comparison Tool – Compare Two Tire Sizes Side by Side
Tire Specifications & Comparison
Select sizes from dropdowns or chart, then compare side by side
TIRE 1CURRENT
WIDTH
Select
ASPECT RATIO
Select
RIM DIAMETER
Select
VS
TIRE 2NEW
WIDTH
Select
ASPECT RATIO
Select
RIM DIAMETER
Select
Select both tire sizes
Calculated Specifications
Sidewall Cross Section
Revolutions Comparison
Comparison Results
Tire 1
Tire 2
Size Differences
Metric
Tire 1
Tire 2
Difference
Speedometer Error
Tire Size Chart
Click rows to select tires for comparison (max 2)
Tire Size
Overall Dia.
Width
Sidewall
Circumference
Revs/Mile
Revs/Km
For reference only. Always verify fitment with a professional before purchasing tires. Diameter difference within 3% is generally safe.
Need to convert tire sizes? Use our free Tire Size Converter for fast and accurate results.
How to Read a Tire Size
A tire size such as 265/70R17 looks like a code, but each part tells you something useful.
The first number is the tire’s section width in millimeters, measured sidewall to sidewall.
The second number is the aspect ratio — the sidewall height shown as a percentage of that width,
so a lower number means a shorter, sportier sidewall. The letter R simply confirms the tire uses
radial construction, which is standard on almost every tire sold today. The final number is the
rim diameter in inches, and it must match your wheel exactly — this is the one measurement that
has zero room for rounding. Once you know these four values, you can calculate the tire’s actual sidewall
height, overall diameter, and circumference, which is exactly what the breakdown below does for you.
265
Section Width
Width in mm, sidewall to sidewall. 265 mm ≈ 10.4″
70
Aspect Ratio
Sidewall height as % of width. Lower = sportier.
R
Radial
Plies run radially at 90°. Standard on all modern tires.
Enter both tire sizes, width, aspect ratio, and rim diameter, into the comparison tool above. It instantly calculates the difference in overall diameter, sidewall height, circumference, and revolutions per mile, so you can see exactly how the two sizes differ before buying.
What tire size difference is considered safe?
As a general rule, a diameter difference within 3% between your old and new tire size is considered safe for most vehicles. Going beyond this range can affect speedometer accuracy, ABS and traction control calibration, and ground clearance.
Can I put a different size tire on my car?
Yes, as long as the new tire’s overall diameter stays close to the original, ideally within 3%. Even if the size numbers look different, two tires can have a very similar overall diameter and roll fine together.
How does tire size affect my speedometer reading?
A tire with a larger overall diameter travels farther per rotation, making your speedometer read slower than your actual speed. A smaller tire makes it read faster. Our comparison tool calculates this speedometer error automatically.
What do the numbers in a tire size like 265/70R17 mean?
The first number, 265, is the section width in millimeters. The second number, 70, is the aspect ratio, or sidewall height as a percentage of width. The R means radial construction, and the last number, 17, is the rim diameter in inches that must match your wheel.
How do I know if two tire sizes will fit the same rim?
The rim diameter, the last number in the tire size, such as 17 in 265/70R17, must be identical between both tires. Width and aspect ratio can vary slightly, but the rim diameter has zero tolerance for rounding.
Does changing tire size affect fuel economy?
Yes. A taller or wider tire increases rolling resistance and rotational mass, which can slightly reduce fuel economy. A shorter or narrower tire may improve it marginally, but the difference is usually small unless the size change is significant.
What is the difference between tire circumference and diameter?
Diameter is the straight-line measurement across the tire from top to bottom. Circumference is the distance around the tire’s outer edge, calculated as diameter multiplied by pi. Circumference determines how far your car travels in one tire revolution.
Can I mix two different tire sizes on the same vehicle?
It’s not recommended for most vehicles, especially those with AWD or 4WD systems, since even small diameter differences can strain the drivetrain. If sizes must differ, keep the difference within the same axle within the 3% safety margin.
Why do revolutions per mile matter when comparing tire sizes?
Revolutions per mile show how many times a tire spins to cover one mile. A tire with more revolutions per mile is smaller in diameter, while fewer revolutions per mile means a larger tire, which directly impacts speedometer accuracy and odometer readings.