Tire Size Converter & Comparison Tool
Convert P-Metric ↔ Flotation and explore results across 4 live tabs: Stats, Visual SVG diagram, Speedometer gauge, and Charts.
REAL-WORLD EXAMPLE
You’re running a stock-size 265/70R17 all-terrain tire on your SUV or truck. That size is roughly 31.6" tall and 10.4" wide, which converts to about 31.6x10.4R17 in flotation format. Stepping up to a 285/75R17 gives an overall diameter of roughly 33.8" — about +2.2" (+7%) taller. Our converter shows the exact diameter, circumference, revs per mile, and speedometer difference so you can see how far that change pushes you beyond the commonly recommended ±3% window for safe plus-sizing.
Tire 1
P-Metric presets:
Tire 2
P-Metric presets:
Acceptable
+1.42%Diameter difference: +0.35" (+1.4%) — acceptable for most builds
225/45R17 Ø
24.97"
634.3mm
235/45R17 Ø
25.33"
643.3mm
Ø Difference
+0.35"
9.0mm
Speedo Error
+1.42%
Speedo reads LOW (taller tire)
Changes within about ±3% are commonly considered a safe starting range for stock vehicles.
| Specification | Tire 1 | Tire 2 | Difference |
|---|---|---|---|
| Section Width (mm) | 225 | 235 | +10 (+4.4%) |
| Aspect Ratio (%) | 45.0 | 45.0 | — |
| Rim Diameter (in) | 17 | 17 | — |
| Sidewall Height (mm) | 101.3 | 105.8 | +4.5 (+4.4%) |
| Sidewall Height (in) | 3.986 | 4.163 | +0.177 (+4.4%) |
| Overall Diameter (mm) | 634.3 | 643.3 | +9.0 (+1.4%) |
| Overall Diameter (in) | 24.97 | 25.33 | +0.35 (+1.4%) |
| Circumference (in) | 78.45 | 79.57 | +1.11 (+1.4%) |
| Revs per Mile | 808 | 796 | -11 (-1.4%) |
| Revs per km | 502 | 495 | -7 (-1.4%) |
Difference = Tire 2 − Tire 1 with % change relative to Tire 1. Values are geometric estimates based on nominal sizes.
AI Insight
Powered by AIGet a plain-English explanation of your results — what they mean for your vehicle and driving experience.
Popular Tire Size Conversions
| From | To | Dia. Diff | Width Diff | Speedo Effect |
|---|---|---|---|---|
| 225/45R17 | 245/45R18 | +1.68" (+6.7%) | +0.79" | ≈ 6–7% low |
| 265/70R17 | 285/75R17 | +2.2" (+7.0%) | +0.79" | ≈ 7% low |
| 235/75R15 | 33x12.5R15 | +4.1" (+14%+) | +2.0" | ≈ 14% low |
| 275/65R18 | 295/65R18 | +0.79" (+2.4%) | +0.79" | ≈ 2–3% low |
These examples illustrate how diameter and width changes translate into speedometer error. Use the converter with your actual sizes to see precise values and whether your change stays within the commonly recommended ±3% diameter window.
How to Use This Converter
- Choose the format for your original tire (P-Metric like 265/70R17, or Flotation like 33x12.50R15).
- Enter the exact size printed on your current tire sidewall.
- Choose the format and enter the new or comparison tire size you are considering.
- Results update live as you type — there is no calculate button.
- Use the four tabs to explore: Stats for the full spec table and P-Metric ↔ Flotation equivalents; Visual for a to-scale SVG side-by-side diagram; Speedometer for the dynamic needle gauge and speed table; Graphs for bar, radar, and speed-curve charts.
- The color-coded Safety badge above the tabs turns green (≤3%), amber (3–5%), or red (>5%) based on the overall diameter difference — use it as a quick fitment sanity check.
Calculation Formulas
About Tire Size Conversion & Plus-Sizing
P-Metric vs Flotation Sizing in Practice
P-Metric sizing (like 225/45R17 or 265/70R17) is standardized and widely used on cars, crossovers, and many SUVs. The three-part code encodes section width in millimetres, aspect ratio as a percentage, and rim diameter in inches. Flotation sizing (like 33x12.50R15) is popular for trucks and off-road builds and expresses overall diameter and section width directly in inches. Understanding both systems is key when you are moving between OEM-style sizes and the “33-inch / 35-inch” language common in off-road communities.
Why Accurate Conversion Matters
Even a seemingly small diameter change alters gearing, engine rpm at cruise, speedometer and odometer readings, and electronic systems that depend on wheel-speed inputs. Width and sidewall changes affect clearance, ride quality, and handling. This converter makes those impacts visible by showing exact changes in diameter, circumference, revs per mile, and speedometer error before you buy tires, helping you avoid combinations that exceed your vehicle’s tolerances or require unexpected modifications.
Using the ±3% Rule as a Starting Point
Many tire and fitment specialists use a ±3% limit on overall diameter as a general guideline for safe size changes on stock vehicles. Staying within that range keeps most speedometers, ABS systems, and traction control logic working as intended and minimizes the risk of rubbing. Larger changes are possible on some platforms, especially with lift kits or bodywork changes, but they demand more careful planning and testing. Use this tool to quickly see where your new size falls relative to that threshold, then combine it with real-world fitment checks for a complete picture.
Four Ways to Read Your Results
The Stats tab gives you the complete numeric breakdown — diameter, width, sidewall height, circumference, and revs per mile in both imperial and metric, plus the P-Metric ↔ Flotation equivalent for each tire. The Visual tab renders both tires as a to-scale SVG so a +2" diameter jump is immediately obvious rather than just a number. The Speedometer tab shows a dynamic needle gauge alongside a table of actual vs indicated speed at common highway readings. The Graphs tab offers a bar chart for direct dimension comparison, a radar chart showing a multi-metric fingerprint of both tires, and a speed-curve chart plotting how actual speed diverges from indicated speed across the full range.