Tire Size Calculator — Compare 225/65R17 vs 205/55R16

Quick answer

Compare tire sizes instantly: a 225/65R17 is 28.5″ tall and 8.9″ wide.

Enter two sizes to see diameter, sidewall, revs/km and speedometer difference — free.

Figures are estimates from this calculator’s standard formula — adjust the inputs in the tool below for your exact number.

Common tire sizes and their overall diameters

Size	Overall diameter (in)	Width (in)
195/65R15	25.0	7.7
205/55R16	24.9	8.1
225/65R17	28.5	8.9
245/45R18	26.7	9.6
275/55R20	31.9	10.8

How Tire Size Calculation Works

Diameter = (2 × Section Width × Aspect Ratio / 25.4) + Rim Diameter | Circumference = π × Diameter

Tire sizes use a standardized notation (e.g., 225/45R17). The first number is width in millimeters, the second is aspect ratio (sidewall height as % of width), and the third is rim diameter in inches. This calculator converts these to actual dimensions.

1
Enter Tire Size
Input tire notation like 225/45R17
2
View Dimensions
See calculated width, height, diameter, and circumference
3
Compare Sizes
Optionally enter second tire size for comparison
4
Check Fitment
Review speedometer error and clearance impact

Use Cases

Size Comparison

Compare dimensions when considering alternative tire sizes

Speedometer Accuracy

Calculate speedometer error when changing tire sizes

Fitment Planning

Ensure new tires will fit without rubbing

Plus Sizing

Calculate correct tire size when upgrading wheel diameter

Tips

1
Stay within 3% of overall diameter to maintain accurate speedometer
2
Larger diameter tires will make speedometer read slower (actual speed is higher)
3
Lower profile tires (lower aspect ratio) provide better handling but harsher ride
4
Wider tires may rub on suspension or fenders when turning
5
Always verify fitment with manufacturer specifications or fitment guides

Common Mistakes

Ignoring speedometer error when changing tire sizes
Not checking clearance for width changes, especially on lowered vehicles
Assuming same aspect ratio means same diameter (it doesn't if width changes)
Forgetting that load rating and speed rating must meet or exceed OEM specs

FAQs

What do tire size numbers like 225/65R17 mean?

225 is the tire width in millimetres, 65 is the sidewall height as a percentage of the width, R means radial construction, and 17 is the wheel diameter in inches. Overall diameter = rim + 2 × sidewall height.

How does changing tire size affect my speedometer?

A taller overall diameter makes your real speed higher than the speedometer shows. Enter both sizes in the calculator to get the exact percentage difference and the speed error at 100 km/h.

How much diameter difference is acceptable?

The practical rule is to stay within 3% of the original overall diameter so the speedometer, ABS and stability systems keep working within tolerance.

Can I fit wider tires than stock?

Usually yes within a narrow range, but check wheel-arch clearance at full lock and full suspension compression, and keep the load and speed indexes at or above the original specification.

How do I read load and speed indexes like 94V?

94 is the maximum load per tire (670 kg) and V is the maximum speed rating (240 km/h). Neither should be lower than the indexes on your car’s original tires.

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