Tyre Size Visualizer
The smarter way to plan a premium-brand tyre or alloy upgrade. See — to the millimetre — how a new size changes your wheel's diameter, sidewall and speedometer reading before you commit.
Precision sizing
Millimetre-accurate diameter, sidewall and circumference comparisons.
Speedo & ABS safe
Stay within the 2–3% tolerance the DVSA and your ECU expect.
Premium-brand ready
Plan fitments around Michelin, Continental, Pirelli, Goodyear & Bridgestone.
How a tyre size works
Example: 225/45 R17
225 — Width
Tread width in millimetres.
45 — Aspect ratio
Sidewall height as % of the width (45% of 225 = 101 mm).
17 — Wheel diameter
Rim size in inches (× 25.4 = mm).
The size you have now
mm — tread width across the tyre
% — sidewall is 113 mm (55% of 205)
inches — × 25.4 = 406 mm
The size you're thinking of fitting
mm — tread width across the tyre
% — sidewall is 101 mm (45% of 225)
inches — × 25.4 = 432 mm
Side-by-side comparison
Overall diameter
632 → 634 mm
+2.4 mm (+0.38%)
Sidewall height
113 → 101 mm
-11.5 mm (-10.20%)
Rolling circumference
1985 → 1993 mm
+7.5 mm (+0.38%)
Diameter change
+0.38%
Speedo reading at actual 70 mph
69.7 mph
Within ideal tolerance (≤ 1.5%).
UK Construction & Use Regulations: indicated speed must never be lower than actual, and no more than 10% + 6.25 mph higher. Keep diameter change within 2–3% as a rule of thumb.
Ready to shop?
Browse tyres & alloy wheels from UK suppliers.
Reading a tyre size
Example: 205/55 R16 91V
- 205 — section width in mm
- 55 — aspect ratio (sidewall as % of width)
- R — radial construction
- 16 — wheel diameter in inches
- 91 — load index (615 kg)
- V — speed rating (240 km/h)
Load & speed checklist
- • New tyres must equal or exceed the original load index.
- • Speed rating must match or exceed your vehicle's V-max.
- • Run-flat (RFT) and standard tyres should not be mixed on one axle.
- • Re-calibrate TPMS after a wheel size change.
- • Check arch clearance and brake caliper clearance with bigger rims.
Why fit premium tyres?
Tyres are the only part of your car that ever touches the road — four contact patches each the size of a postcard. Premium brands such as Michelin, Continental, Pirelli, Goodyear, Bridgestone and Dunlop consistently top independent wet-braking, dry-handling and tread-life tests run by Auto Express, Auto Bild and the ADAC. Choosing a premium tyre — and fitting it in the correct size — is the single biggest safety and refinement upgrade you can make to any car.
What this visualizer is for
Our Tyre Size Visualizer is a free, professional-grade fitment calculator. Enter your current tyre size and the size you're considering and you'll instantly see the overall diameter, sidewall height, rolling circumference and the resulting speedometer error rendered against a true-to-scale side-by-side preview. It's the same maths a fitting bay uses — only faster, and without the upsell.
- Plan a plus-1 or plus-2 alloy upgrade without breaking your speedometer or ABS calibration.
- Check whether a winter tyre on a smaller rim keeps the same rolling diameter as your summer set.
- Verify load and speed ratings before you commit to a premium-brand set.
- Confirm arch and caliper clearance before ordering new alloys.
Buying tyres the right way
We only recommend new tyres from reputable manufacturers with full UK type-approval, a current EU tyre label and a date code less than two years old. Buy from established fitters and authorised distributors — your tyres are a safety component and deserve the same standard of care as your brakes. A correctly specified premium tyre will out-brake, out-last and out-quiet a cut-price alternative on every measurable axis, and the cost-per-mile is usually lower over the life of the tyre.
When the visualizer shows a size you like, jump straight into our Tyres & Wheels marketplace to compare current pricing from UK suppliers, or use the Tyre Finder and Wheel Finder to narrow by brand, size and load rating.
FAQ
What is plus-sizing?
Fitting a larger-diameter wheel with a lower-profile tyre to keep the overall rolling diameter (and therefore speedo accuracy) the same. Plus 1 = +1" wheel, Plus 2 = +2", etc.
How much speedo error is acceptable?
UK law requires the indicated speed must never be lower than actual, and no more than 10% + 6.25 mph higher. Aim to keep the new size within 2–3% of the original diameter.
Will plus-sizing affect my ride?
Yes — lower profiles give sharper steering response but a firmer ride and more risk of pothole damage. Heavier alloys can also reduce acceleration and economy slightly.