Do bigger tyres affect fuel economy and acceleration?

They can. A larger overall diameter effectively lengthens the gearing, so acceleration softens slightly and the engine turns fewer revs at motorway speeds, while heavier or wider tyres add rolling resistance and aerodynamic drag. Differences within the usual 2% diameter window are rarely noticeable day to day; the further you move from the original size, the more you will feel it.

Sizes & pressures

Tire Size Calculator

Q: How do I read a tyre size like 205/55 R16?

The first number (205) is the tyre's width in millimetres. The second (55) is the profile, or aspect ratio - the sidewall height as a percentage of the width, so here the sidewall is 55% of 205mm. The R means radial construction, and the final number (16) is the rim diameter in inches. A full marking usually ends with a load index and speed rating, for example 91V.

Q: How much speedometer error is acceptable?

The calculator estimates the change caused by tyre diameter, not your vehicle’s existing speedometer error or legal compliance. A larger diameter increases distance travelled per wheel revolution; the displayed road-speed estimate assumes the original calibration was exact.

Q: What are plus sizing and minus sizing?

Plus sizing fits a larger rim with a wider, lower-profile tyre while keeping the overall diameter close to standard - Plus 1 means a one inch larger rim, Plus 2 two inches. It typically sharpens steering response at some cost in comfort. Minus sizing is the reverse - a smaller rim with a taller sidewall - and is popular for winter tyres, because narrower tyres cut through snow better and smaller sizes usually cost less.

Compare tire dimensions, alternative sizes and the change in your speedometer reading.

Use this tool

Single Size: Enter your tire size to view specs and find alternatives

Compare Two: Enter both sizes to see diameter differences and speedometer errors

Quick Compare: Click any alternative size to instantly compare it

Try these popular comparisons: 225/45R17 vs 235/40R18 265/70R17 vs 275/60R20 245/40R19 vs 255/35R20 205/55R16 alternatives

The 3D view compares two tires. Add a second size to see it.

Original Tire Size

Width (mm) / Profile (%) R Rim (")

New Tire Size (optional)

Width (mm) / Profile (%) R Rim (")

Your size change, explained

205/55 R16

Nominal geometry, not fitment approval. A small diameter difference does not prove that a tire fits your vehicle.

Diameter: 631.9 mm
Rim: 16.0″
Sidewall Height: 112.8 mm
Width: 205.0 mm

The 3D view compares two tires. Add a second size to see it.

To-scale nominal diameters and rims. Illustrative cross-sections, not a vehicle clearance simulation.

Calculator Results Charts Visual Alternatives

Measurement	Original	New	Difference	%
Width
Diameter
Circumference
Sidewall Height
Revolutions per km

Diameter

Speedometer

Ride Height

Sidewall Height

Visual Comparison

Wheel Spacing

Rotation Speed

● Original (Gunmetal) ● Comparison (Bronze)

Tip: Click Overlay to stack both tires on top of each other and see the exact size difference. Use the camera buttons to view from different angles.

Drag to rotate • Scroll to zoom • Right-click to pan

Alternative Tire Sizes

Alternative sizes are geometric suggestions, not a verified stock list or fitment approval. Diameter tolerances are search filters, not safety limits.

These alternative sizes maintain a similar overall diameter (within ±2%) to your original tire.

Tire Size FAQs

How do I read a tire size like 205/55 R16?

The first number (205) is the tire's width in millimeters. The second (55) is the profile, or aspect ratio - the sidewall height as a percentage of the width, so here the sidewall is 55% of 205mm. The R means radial construction, and the final number (16) is the rim diameter in inches. A full marking usually ends with a load index and speed rating, for example 91V.

Can I fit a different tire size on my car?

Use a vehicle-approved size and check wheel specifications, load and speed ratings, and clearance. A close diameter match alone is not approval. Ask a qualified tire professional if the proposed fitment is not documented.

How much speedometer error is acceptable?

The calculator estimates the change caused by tire diameter, not your vehicle’s existing speedometer error or legal compliance. A larger diameter increases distance travelled per wheel revolution; the displayed road-speed estimate assumes the original calibration was exact.

What are plus sizing and minus sizing?

Plus sizing fits a larger rim with a wider, lower-profile tire while keeping the overall diameter close to standard - Plus 1 means a one inch larger rim, Plus 2 two inches. It typically sharpens steering response at some cost in comfort. Minus sizing is the reverse - a smaller rim with a taller sidewall - and is popular for winter tires, because narrower tires cut through snow better and smaller sizes usually cost less.

Do bigger tires affect fuel economy and acceleration?

They can. A larger overall diameter effectively lengthens the gearing, so acceleration softens slightly and the engine turns fewer revs at motorway speeds, while heavier or wider tires add rolling resistance and aerodynamic drag. Differences within the usual 2% diameter window are rarely noticeable day to day; the further you move from the original size, the more you will feel it.

Also try our Tire Pressure Calculator.

How the calculator works

This calculator uses the size marked on the sidewall. The result is unloaded, theoretical geometry; actual dimensions vary by tire model, wheel width and operating conditions.

Sidewall (mm): width × aspect ratio ÷ 100
Diameter (mm): rim inches × 25.4 + 2 × sidewall
Circumference (mm): π × diameter
Calculated speed: indicated speed × new diameter ÷ original diameter

Worked example: 205/55 R16 → 225/45 R17

The nominal diameters are 631.9 mm and 634.3 mm: an increase of about 0.38%. Radius increases by 1.2 mm, sidewall height falls by 11.5 mm, and an indicated 100 km/h corresponds to about 100.4 km/h under the calibration assumption above.

Before you change size

Check the vehicle-approved sizes, wheel width and offset, load and speed ratings, brake and bodywork clearance, and any AWD or staggered-fitment requirements. This tool cannot approve any of these.

Source: Michelin guidance on changing tire size

Important Notice

All measurements, diameter calculations, speedometer error estimations, and alternative size suggestions provided by this calculator are theoretical values derived from nominal tire size specifications using standard industry formulas.

Actual tire dimensions may vary from calculated values. Tire manufacturers are permitted to produce tires within established manufacturing tolerances as defined by industry standards (ETRTO, T&RA). Actual tire dimensions can differ based on manufacturing tolerances, tread design, inflation pressure, rim width, and load conditions. Always verify fitment compatibility with your vehicle manufacturer's specifications and consult a qualified tire professional before making any tire size changes. This tool is provided for informational purposes only and should not be considered as professional advice or a guarantee of fitment or safety.