265/40R21
Overall diameter 745.4 mm
265/40R21 — 745.4 mm tall, and what it swaps with
265/40R21 is 265 mm wide with a 40% sidewall on a 21-inch wheel. That sidewall is 106 mm, so the tyre stands 745.4 mm tall and turns 427 times per kilometre.
- Section width
- 265 mm
- Aspect ratio
- 40 %
- Wheel size
- 21 in (533.4 mm)
- Sidewall height
- 106 mm
- Overall diameter
- 745.4 mm (29.35 in)
- Circumference
- 2341.7 mm
- Turns per km
- 427
Sizes you can swap to
Only sizes whose overall diameter stays within 3% are listed. A different diameter covers a different distance per turn, and that gap becomes speedometer error.
265/45R20746.5 mm · +0.15% you go faster265/35R22744.3 mm · -0.15% you go slower265/50R19747.6 mm · +0.3% you go faster305/30R22741.8 mm · -0.48% you go slower245/70R16749.4 mm · +0.54% you go faster235/55R19741.1 mm · -0.58% you go slower245/65R17750.3 mm · +0.66% you go faster295/35R21739.9 mm · -0.74% you go slower245/60R18751.2 mm · +0.78% you go faster275/35R22751.3 mm · +0.79% you go faster235/60R18739.2 mm · -0.83% you go slower245/55R19752.1 mm · +0.9% you go faster
Same profile, different width
Other sizes for this wheel
21-inch wheels
245/35R21 704.9mm245/40R21 729.4mm245/45R21 753.9mm255/35R21 711.9mm255/40R21 737.4mm265/35R21 718.9mm265/40R21 745.4mm265/45R21 771.9mm275/30R21 698.4mm275/35R21 725.9mm275/40R21 753.4mm275/45R21 780.9mm285/30R21 704.4mm285/35R21 732.9mm285/40R21 761.4mm295/35R21 739.9mm305/30R21 716.4mm315/30R21 722.4mm
How the code reads
The 205 is millimetres, the 55 is a percentage of that width, and only the 16 is inches. The R stands for radial construction.
How to read this
- The first three digits are the width in mm, the middle two are the aspect ratio in percent, the last two the wheel in inches.
- Sidewall height = width × aspect ÷ 100. For 205/55 that is 112.75 mm.
- Overall diameter = wheel diameter + twice the sidewall. A 16-inch wheel is 406.4 mm.
- Once the diameter shifts by more than 3%, the speedometer and odometer drift by the same amount.
Frequently asked questions
Q. What is the overall diameter of 265/40R21?
745.4 mm — the 533.4 mm wheel plus the 106 mm sidewall at top and bottom.
Q. How many turns per kilometre does 265/40R21 make?
Its circumference is 2341.7 mm, so 427 turns.
Q. What can I swap it for?
12 sizes stay within 3% of its diameter — the closest is 265/45R20 at 746.5 mm.
Q. Why is the sidewall 106 mm?
Because it is 40% of the 265 mm width. The aspect ratio is a proportion of the width, not a length.