Compare Tyre Sizes Calculator

Comparison only. Leave at 0 to compare against the tire entered above.
Leave at 0 for a single-tire calculation with no comparison.
Used to show what the new tire is really doing when the dial reads this figure.
Diameter difference
-0.08 %
Tire Size Calculator
Tire size
205/55R16
Sidewall height
112.75 mm
Sidewall height
4.439 in
Overall diameter
631.90 mm
Overall diameter
24.878 in
Section width
8.071 in
Circumference
1,985.17 mm
Circumference
78.156 in
Revolutions per mile
810.68 rev/mi
Revolutions per kilometre
503.73 rev/km
Original tire diameter
631.90 mm
New tire size
225/50R16
New tire sidewall height
112.50 mm
New tire diameter
631.40 mm
New tire revolutions per mile
811.32 rev/mi
Diameter difference
-0.50 mm
Circumference difference
-0.08 %
Ride height change
-0.25 mm
True speed when the dial reads the indicated speed
59.95
Speedometer error
-0.08 %
Worked out from NHTSA, Tire terminology and size designation and 4 other sources.
These are nominal dimensions derived from the size code. A mounted tire measures slightly differently depending on rim width, inflation pressure, load and wear.

How this is worked out

6 steps
  1. Sidewall height h = 205 x 55 / 100 = 112.75 mm.
  2. Overall diameter d = 16 x 25.4 + 2 x 112.75 = 631.9 mm.
  3. Circumference c = pi x 631.9 = 1985.1724 mm.
  4. Revolutions per mile = 1,609,344 / 1985.1724 = 810.682.
  5. New tire diameter = 631.4 mm, a change of -0.5 mm (-0.0791%).
  6. At an indicated 60 mph the vehicle is really doing 59.953.

Results are general information, not financial, tax, legal, medical or engineering advice.