Wheel Sizing & Conversion

Equivalent Diameter Tire Finder

Find every tire size within a chosen percent of your stock diameter across several rim sizes. Ranked list with mm, inch and percent gaps.

Wheel Sizing & Conversion

Find sizes near a target diameter.

Open Live Calculator

Equivalent Diameter Tire Finder: Tire Size Inputs

Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.

ISO/TRA Compliant

Baseline Tire (T1)Stock OEM

Width (mm)

Aspect (%)

Rim (in)

Comparison Tire (T2)Proposed Setup

Width (mm)

Aspect (%)

Rim (in)

Baseline OD634.3 mm24.97"

Comparison OD637.2 mm25.09"

Diameter Variance+2.9 mm+0.46%

Speed @ 60 MPH60.3 MPH-4 revs/mi

How Equivalent Diameter Tire Finder Works?

The Equivalent Diameter Tire Finder works by testing every standard width, aspect ratio and rim combination and keeping the sizes whose diameter falls within the chosen tolerance of the stock tire. The search runs in 4 steps.

Enter the stock size
Type the original size, for example 225/45 R17, to set the target diameter of 634.3 mm (24.97 in).
Choose rim sizes
Select the wheel diameters to search, for example 16 to 20 inches.
Set a tolerance
Pick a limit such as ±1% or ±3% of the target diameter.
Review the matches
The finder lists every match sorted from the smallest to the largest diameter gap.

Equivalent Diameter Tire Finder Formula

The Equivalent Diameter Tire Finder keeps a candidate size when |OD_c − OD_t| ÷ OD_t × 100 ≤ Tolerance.

Candidate diameterOD_c = 2 × W × AR ÷ 100 + Rim × 25.4

Match test|OD_c − OD_t| ÷ OD_t × 100 ≤ T

Search spaceW = 185…335 (step 10), AR = 25…85 (step 5), Rim = chosen set

OD_t: Target diameter from the stock size (mm)
OD_c: Candidate diameter (mm)
T: Tolerance (%)

Worked example

With 225/45 R17 as the target (634.3 mm), the candidate 245/40 R18 measures 653.2 mm. The gap is +2.98%, which fails a ±1% search and passes a ±3% search. The candidate 225/40 R18 sits at +0.46% and passes both.

Equivalent Diameter Tire Finder Conversion Table

The Equivalent Diameter Tire Finder conversion table lists the 10 closest equivalent sizes for a 225/45 R17 tire across 5 rim diameters.

10 closest matches for 225/45 R17 on 16–20 inch rims (±1%)
Size	Diameter (mm)	Diameter (in)	Gap vs 225/45 R17
225/45 R17	634.3 mm	24.97 in	+0.00%
215/35 R19	633.1 mm	24.93 in	-0.19%
255/30 R19	635.6 mm	25.02 in	+0.20%
255/35 R18	635.7 mm	25.03 in	+0.22%
255/40 R17	635.8 mm	25.03 in	+0.24%
195/45 R18	632.7 mm	24.91 in	-0.25%
255/45 R16	635.9 mm	25.04 in	+0.25%
205/55 R16	631.9 mm	24.88 in	-0.38%
205/50 R17	636.8 mm	25.07 in	+0.39%
215/30 R20	637.0 mm	25.08 in	+0.43%

What is Equivalent Diameter Tire Finder?

An Equivalent Diameter Tire Finder is a search tool that returns every tire size with nearly the same overall diameter as a reference tire. The finder replaces trial and error with a full search of standard sizes.

A typical search for one target diameter across 5 rim sizes returns 15 to 40 sizes inside ±3% and 5 to 15 sizes inside ±1%.

The results are nominal. A shortlisted size still needs a load index, speed rating and rim width check before purchase.

What are the uses of Equivalent Diameter Tire Finder?

There are 4 main uses of the Equivalent Diameter Tire Finder, including wheel upgrades and availability problems.

Wheel upgrades
List sizes that keep speedometer accuracy on a larger wheel.
Availability problems
Find a substitute size when the stock size is out of stock.
Cost savings
Find a more common, lower-cost size with the same diameter.
Width changes
Find a wider or narrower size with the same height.