Tire Size Calculator
Decode any tire size code — get diameter, sidewall height, circumference, and revolutions per mile. Compare two sizes and check speedometer accuracy.
Tire Size Calculator
Decode · Compare · Speedometer
28.52in / 724mm
Overall Diameter
5.76in / 146mm
Sidewall Height
89.58in
Circumference
707
Revolutions/Mile
HOW TO READ A TIRE SIZE
Decoding the Tire Size Code — 225/65R17
Every metric tire has a standardized code on the sidewall. Here's what each number means.
COMMON SIZES
Popular Tire Sizes — Dimensions at a Glance
All dimensions computed live from the section-width / aspect-ratio / rim formula above.
| Tire Size | Diameter (in) | Width (in) | Sidewall (in) | Circumference (in) | Rev/Mile | Common Vehicles |
|---|---|---|---|---|---|---|
| 195/65R15 | 24.98" | 7.68" | 4.99" | 78.48" | 807 | Honda Civic, Toyota Corolla (older) |
| 205/55R16 | 24.88" | 8.07" | 4.44" | 78.16" | 811 | VW Golf, Toyota Camry, Honda Accord |
| 215/60R16 | 26.16" | 8.46" | 5.08" | 82.18" | 771 | Toyota Camry, Honda CR-V |
| 225/45R17 | 24.97" | 8.86" | 3.99" | 78.45" | 808 | BMW 3 Series, Audi A4 |
| 225/65R17 | 28.52" | 8.86" | 5.76" | 89.58" | 707 | Toyota RAV4, Honda CR-V, Mazda CX-5 |
| 235/55R17 | 27.18" | 9.25" | 5.09" | 85.38" | 742 | Ford Edge, Chevy Equinox |
| 235/65R17 | 29.03" | 9.25" | 6.01" | 91.19" | 695 | Ford Escape, Jeep Compass |
| 245/45R18 | 26.68" | 9.65" | 4.34" | 83.82" | 756 | BMW 5 Series, Audi A6 |
| 255/55R18 | 29.04" | 10.04" | 5.52" | 91.24" | 694 | Ford Explorer, Chevy Traverse |
| 265/70R17 | 31.61" | 10.43" | 7.30" | 99.29" | 638 | Ford F-150, Chevy Silverado (stock) |
| 275/60R20 | 32.99" | 10.83" | 6.50" | 103.65" | 611 | RAM 1500, GMC Sierra |
| 285/50R22 | 33.22" | 11.22" | 5.61" | 104.37" | 607 | GMC Yukon Denali, Cadillac Escalade |
⚠️ Stay Within 3% of Original Diameter When Upsizing
Exceeding a 3% difference in overall diameter affects speedometer accuracy, ABS and traction control calibration, and odometer readings. A 3% larger diameter changes your speed reading by roughly 3% without recalibration. Always check for rubbing at full lock and over bumps. Most wheel/tire shops recommend staying within this range.
📏 Low Profile vs High Profile
Low profile (aspect ratio 30-50): shorter sidewall, better handling precision, less cushion through corners, less comfortable on rough roads. Common on sports and performance vehicles.
High profile (aspect ratio 60-80): taller sidewall, more cushioning for rough roads, better for off-road, slightly less precise steering. Common on trucks, SUVs, and economy vehicles.
➕ Plus-Sizing Explained
Plus-sizing means fitting a larger wheel rim with a lower-profile tire while maintaining approximately the same overall diameter. Plus 1 = increase rim by 1 inch with reduced aspect ratio; improved steering response (shorter sidewall flex), better braking, and improved appearance.
The key rule: keep overall diameter within 3% of stock. Going from 225/65R17 to 235/55R18 keeps diameter virtually identical (28.5 vs 28.2in) while improving the wheel-to-tire look and handling feel.
How to Calculate Tire Size Dimensions
All tire dimensions can be calculated from the three numbers in a metric tire code: section width (mm), aspect ratio (%), and rim diameter (inches).
Complete Tire Dimension Formulas
Given tire code: W/A/R (e.g. 225/65R17) W = Section width in mm A = Aspect ratio (%) R = Rim diameter in inches Sidewall height (mm) = W × (A / 100) Overall diameter (mm) = (R × 25.4) + (2 × Sidewall height) Overall diameter (in) = Diameter (mm) / 25.4 Circumference (in) = Diameter (in) × π Revolutions/mile = 63,360 / Circumference (in) Example: 225/65R17 Sidewall height = 65 × 225 / 100 = 146.25mm = 5.76in Overall diameter = (17 × 25.4) + (2 × 146.25) = 431.8 + 292.5 = 724.3mm = 28.52in Circumference = 28.52 × π ≈ 89.58in Revolutions/mile = 63,360 / 89.58 ≈ 707
Speedometer Error Formula
% Diameter change = ((New diameter − Old diameter) / Old diameter) × 100 Actual speed = Indicated speed × (New diameter / Old diameter) If new tire is LARGER: speedometer reads LOW (actual speed > indicated) If new tire is SMALLER: speedometer reads HIGH (actual speed < indicated) Example: Original 28.52in → New 29.50in (+3.4%) At indicated 60 mph: actual = 60 × (29.50/28.52) = 62.1 mph (reads 3.4 mph slow)
Load Index and Speed Rating
After the tire code you'll often see a number and letter (e.g. 95H). The number is the load index — 95 means the tire can support up to 1,521 lbs (690kg). The letter is the speed rating — H means approved for sustained speeds up to 130mph (210km/h). Common speed ratings: T (118mph), H (130mph), V (149mph), W (168mph), Y (186mph).
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