Compara dos tamaños de neumático cualesquiera (por ejemplo, 225/45R17 frente a 245/40R18) en diámetro total, circunferencia, % de error del velocímetro y cambio de holgura.
| Métrica | Neumático A | Neumático B | Δ |
|---|
Formato P-métrico W/AR-D: flanco (mm) = ancho de sección × perfil / 100. Diámetro total (mm) = 2 × flanco + llanta × 25,4. Circunferencia = π × diámetro. Revoluciones/milla = 1 609 344 / circunferencia.
Error del velocímetro a la velocidad indicada = (diámetro B − diámetro A) / diámetro A × velocidad indicada. Positivo = la velocidad real es mayor que la mostrada al usar el neumático B.
Both sizes are parsed from the P-metric code. Sidewall height in millimetres is section width × aspect ÷ 100; overall diameter is twice that plus the rim in inches × 25.4. Circumference is π × diameter, and revolutions per mile are 1,609,344 ÷ circumference in mm. On the defaults, 225/45R17 works out at 634.3 mm and 245/40R18 at 653.2 mm, a +18.9 mm and +2.98% difference, and the table gives you the delta on every derived metric side by side.
Aspect ratio does most of the work, because the sidewall is counted twice. Dropping 225/45R17 to a 40-series costs 22.5 mm of diameter, close to the 25.4 mm a full inch of rim adds, which is exactly why plus-sizing pairs a bigger wheel with a shorter sidewall. Indicated speed and its unit feed only the speedometer line, where true speed = indicated × (diameter B ÷ diameter A); that is why 60 mph on the defaults becomes 61.8. The headline percentage is the number to judge a fitment by.
Everything derives from the printed code, not from a measured tire. Real diameters vary by several millimetres between brands at the same nominal size, and tread wear shrinks them further, so treat roughly a percent as noise. The figures also describe an unloaded tire: under vehicle weight the rolling radius is smaller and true revolutions per mile higher. Only metric sizes containing an R are parsed, so flotation codes are rejected, and clearance is reported as half the diameter change, saying nothing about width.
Just under 3%. The diameters are 634.3 mm and 653.2 mm, a +18.9 mm change, so an indicated 60 mph is actually 61.8 mph on the taller tire. Vertical clearance changes by about 9.5 mm per side.
It trades sidewall for rim diameter. Each inch of wheel adds 25.4 mm of overall diameter, and you claw that back by cutting the aspect ratio, which is why 225/45R17 to 245/40R18 nets only +18.9 mm: the shorter 40-series sidewall counts twice.
225 is the section width in millimetres, 45 is sidewall height as a percentage of that width, giving 101.25 mm here, R means radial construction, and 17 is rim diameter in inches. Overall diameter is two sidewalls plus the rim converted at 25.4 mm.
This only reports half the diameter change as clearance per side, which covers the vertical gap. It knows nothing about section width growth, wheel offset, backspacing or steering sweep, so inner clearance at full lock has to be checked on the car.
The parser looks for the metric pattern of width, slash, aspect, R, rim. Flotation sizes written in inches, and any code with no R in it, fall through and the tool shows its reminder to enter something like 225/45R17 instead.
Battery Life Runtime Calculator (mAh)
Calculate how long a battery lasts at a given current draw — mAh to hours, Wh, and screen-on time.
Fertilizer / Nutrient Dilution Calculator
Dilute liquid fertiliser concentrate to target PPM or EC for soil and hydroponics.
Paper Size Converter (A4 / Letter / B-Series / JIS)
Convert between ISO A/B/C, US Letter / Legal / Tabloid and Japanese JIS paper sizes in mm and inches.
Font Size Converter (pt, px, rem, em, %)
Convert font sizes between pt, px, rem, em and % for web and print typography.
Time Zone Overlap Calculator (Remote Teams)
Find overlapping productive hours across up to 8 time zones for distributed teams.
Word Count to Pages Converter (Book / Essay / Manuscript)
Estimate pages from word count by genre, font, size and spacing — novel, essay, manuscript, blog.
