Wheel Sizing & Conversion

Same-Rim Alternative Size Finder

Find alternative tire sizes that fit your current wheel. Compare narrower and wider options on the same rim diameter with diameter gaps.

Wheel Sizing & Conversion

Compare alternatives on one rim diameter.

Open Live Calculator

Same-Rim Alternative Size 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 Same-Rim Alternative Size Finder Works?

The Same-Rim Alternative Size Finder works by holding the rim diameter fixed and finding the aspect ratio for each width that comes closest to the stock diameter. The tool uses 3 steps.

Enter the stock size
Type the current size, for example 215/55 R17.
Pick the width range
Choose widths to test, for example 195 mm to 245 mm (7.7 in to 9.6 in).
Review alternatives
The finder lists the best aspect ratio for each width, the diameter and the gap from stock.

Same-Rim Alternative Size Finder Formula

The Same-Rim Alternative Size Finder picks, for each width W, the aspect ratio AR that minimizes |OD(W, AR, Rim) − OD_stock|.

Ideal aspect ratioAR* = (OD_stock − Rim × 25.4) ÷ (2 × W) × 100

Chosen aspect ratioAR = nearest multiple of 5 to AR*

GapΔ% = (OD − OD_stock) ÷ OD_stock × 100

W: Candidate width (mm)
AR*: Exact aspect ratio for equal diameter
Rim: Fixed rim diameter (in)

Worked example

On the 17-inch wheel of a 215/55 R17 tire (668.3 mm), a 235 mm width needs an ideal aspect ratio of 50.3%. The nearest real size is 235/50 R17 at 666.8 mm (-0.22%).

Same-Rim Alternative Size Finder Conversion Table

The Same-Rim Alternative Size Finder conversion table lists the closest-diameter size for 6 widths on a 17-inch (431.8 mm) wheel, using 215/55 R17 as stock.

Best alternative per width for a 215/55 R17 wheel
Size	Width change	Diameter (mm)	Diameter (in)	Gap vs stock
195/60 R17	-20 mm	665.8 mm	26.21 in	-0.37%
205/60 R17	-10 mm	677.8 mm	26.69 in	+1.42%
215/55 R17	+0 mm	668.3 mm	26.31 in	+0.00%
225/55 R17	+10 mm	679.3 mm	26.74 in	+1.65%
235/50 R17	+20 mm	666.8 mm	26.25 in	-0.22%
245/50 R17	+30 mm	676.8 mm	26.65 in	+1.27%

What is Same-Rim Alternative Size Finder?

A Same-Rim Alternative Size Finder is a tool that lists the tire sizes that keep the current wheels and stay close to the stock diameter. Changing tire size without changing wheels is the lowest-cost size change.

Each 10 mm width step changes sidewall height, so the aspect ratio shifts one step down for wider tires and one step up for narrower tires.

Each alternative still needs a rim width check. A 245 mm tire on a 6.5-inch rim falls outside most tire makers' approved range.

What are the uses of Same-Rim Alternative Size Finder?

There are 4 main uses of the Same-Rim Alternative Size Finder, including wider tires on stock wheels and winter narrowing.

Wider tires on stock wheels
Gain grip with a wider size that keeps the factory wheel.
Winter narrowing
Pick a narrower winter size for the same wheel.
Availability
Find a nearby size when the factory size is scarce.
Budget options
Find a common size with lower prices for the same wheel.