305/30R20
Overall diameter 691 mm
305/30R20 — 691 mm tall, and what it swaps with
305/30R20 is 305 mm wide with a 30% sidewall on a 20-inch wheel. That sidewall is 91.5 mm, so the tyre stands 691 mm tall and turns 460.7 times per kilometre.
- Section width
- 305 mm
- Aspect ratio
- 30 %
- Wheel size
- 20 in (508 mm)
- Sidewall height
- 91.5 mm
- Overall diameter
- 691 mm (27.2 in)
- Circumference
- 2170.8 mm
- Turns per km
- 460.7
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.
235/55R17690.3 mm · -0.1% you go slower235/50R18692.2 mm · +0.17% you go faster215/60R17689.8 mm · -0.17% you go slower265/35R20693.5 mm · +0.36% you go faster235/60R16688.4 mm · -0.38% you go slower235/45R19694.1 mm · +0.45% you go faster255/45R18686.7 mm · -0.62% you go slower255/40R19686.6 mm · -0.64% you go slower255/35R20686.5 mm · -0.65% you go slower225/70R15696 mm · +0.72% you go faster215/65R16685.9 mm · -0.74% you go slower225/45R19685.1 mm · -0.85% you go slower
Same profile, different width
Other sizes for this wheel
20-inch wheels
235/35R20 672.5mm235/45R20 719.5mm235/55R20 766.5mm245/30R20 655mm245/35R20 679.5mm245/40R20 704mm245/45R20 728.5mm245/50R20 753mm255/30R20 661mm255/35R20 686.5mm255/40R20 712mm255/45R20 737.5mm255/50R20 763mm265/30R20 667mm265/35R20 693.5mm265/40R20 720mm265/45R20 746.5mm265/50R20 773mm275/30R20 673mm275/35R20 700.5mm275/40R20 728mm275/45R20 755.5mm275/55R20 810.5mm285/30R20 679mm285/35R20 707.5mm285/40R20 736mm285/50R20 793mm295/30R20 685mm295/35R20 714.5mm305/30R20 691mm315/35R20 728.5mm
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 305/30R20?
691 mm — the 508 mm wheel plus the 91.5 mm sidewall at top and bottom.
Q. How many turns per kilometre does 305/30R20 make?
Its circumference is 2170.8 mm, so 460.7 turns.
Q. What can I swap it for?
12 sizes stay within 3% of its diameter — the closest is 235/55R17 at 690.3 mm.
Q. Why is the sidewall 91.5 mm?
Because it is 30% of the 305 mm width. The aspect ratio is a proportion of the width, not a length.