Does the calculator account for wheel width and offset?

No. It calculates nominal tyre geometry; wheel width, offset, centre bore, fixings and arch clearance are not assessed.

Why can actual tyre diameter differ from the calculation?

The formula uses nominal markings. Brand, model, wheel width, pressure, load and tread wear alter the real dimensions.

Tyre Size Comparison

Enter two tyre sizes

Current sizeStarting point

Tyre dimensions

Width Aspect ratio Rim

New sizeSize you are considering

Tyre dimensions

Width Aspect ratio Rim

205/55 R16 means a 205 mm width, 55% aspect ratio and 16-inch rim.

Very small difference

205/55 R16 → 225/45 R17

Diameter change+0,38 %

Visual comparison

205/55 R16Current

225/45 R17New

Key changes

Ground clearance+1,2 mmthe vehicle would theoretically rise

Actual speed100,4 km/hwhen the speedometer shows 100 km/h

Actual distance100,4 kmwhen the odometer records 100 km

Check another indicated speed

km/h

Detailed tyre dimension comparison

Nominal theoretical dimensions calculated from the tyre marking.

Measurement	205/55 R16	225/45 R17	Difference
Tyre width
Sidewall height
Rim diameter
Overall diameter
Theoretical circumference
Revolutions per kilometre

Speedometer comparison

Theoretical road speed if the vehicle was calibrated for the first tyre size.

Indicated speed	Theoretical road speed	Difference

Important: this calculation isolates the effect of nominal tyre size. Factory calibration, pressure, load, tread wear and actual model dimensions also affect the reading.

Extra tool

Equivalent tyre sizes

Using 205/55 R16 find the closest nominal-diameter options for your chosen rim.

Mathematically close diameter options for rim R17. This does not confirm availability or suitability for a particular vehicle and wheel.

Tyre size	Diameter difference	Ground clearance	Speed at 100 km/h	Action

How to compare tyre sizes

From the sidewall marking to clear diameter and speedometer changes

Find your current size

Check the tyre sidewall or vehicle placard and enter a size such as 205/55 R16.

Enter the new size

Select the size you are considering; the standard 225/45 R17 format is used.

Compare the changes

Review sidewall height, diameter, circumference, clearance, revolutions and theoretical speedometer readings.

Check the vehicle documents

A mathematically close size is not automatically suitable. Always use sizes approved by the vehicle manufacturer.

What does tyre size 205/55 R16 mean?

Three main numbers describe the nominal tyre dimensions

205/55R16

205 – width

Nominal section width in millimetres.

55 – aspect ratio

The sidewall height is 55% of the width: 112.75 mm here.

R16 – construction and rim

R means radial construction and 16 is the rim diameter in inches.

205/55 R16 vs 225/45 R17

Tyre size calculator FAQs

Answers about sidewall height, changing R16 to R17, speedometer difference and equivalent sizes

How do you calculate tyre sidewall height?

What is the difference between 205/55 R16 and 225/45 R17?

Which tyres can replace 205/55 R16?

Can R16 tyres be changed to R17?

How does tyre size affect the speedometer?

What tyre-diameter difference is acceptable?

How does ground clearance change?

Does the tool check wheel width and offset?

Why can actual tyre size differ from the result?

Does the calculator save entered sizes?