Is a “likely OK” fit street-legal?

This tool does not certify legality. Wrong load/speed ratings or rubbing arches are still failures. Ask a tyre fitter.

Where is the DOT code?

On the sidewall, often near “DOT”. The last four digits of the complete code are week and year of manufacture.

Can I mix sizes front and rear?

Only if the manufacturer specifies a staggered setup (common on performance cars). Do not invent your own staggered fitment.

Tyre tools

Tyre size, tread & age checkers

Check whether a plus-size tyre is in the safe diameter ballpark, read tread depth against UK law, decode DOT week/year ageing, and convert PSI ↔ bar.

Can I fit these tyres?

Stock size (from door sticker)Proposed size

Likely OK

Diameter within ~1.5% and modest width/rim change — still confirm load/speed ratings and arch clearance.

205/55R16 ⌀632mm → 225/45R17 ⌀634mm (+0.38%)

Tread depth

Depth (mm)

Monitor

Still decent for many conditions. Recheck monthly and before long trips.

Tyre age (DOT code)

Last 4 digits of DOT (WWYY)

Week 23, 2019 · ~7.4 years old

Ageing rubber — inspect for cracks/bulges yearly even if tread looks fine.

PSI ↔ bar

PSIbar

What these checkers do

Size fit compares overall diameter of a stock size vs a proposed size. Staying within ~1.5–3% is a common rule of thumb — load/speed ratings, offset and arch clearance still matter.

UK legal minimum tread is generally 1.6mm across the central three-quarters of the tread around the full circumference. Many drivers renew nearer 3mm for wet grip.

DOT date codes end in four digits (WWYY). Tyres can look fine but crack with age — makers often advise inspection/replacement around 6–10 years.

Examples

205/55R16 → 225/45R17

A common plus-one look. Diameter is often close — still confirm with a tyre professional before buying alloys.

2.0mm tread

Still legal, but wet braking is already compromised versus a new tyre. Plan replacement.

DOT 2319

Week 23 of 2019 — check age against today’s date and inspect sidewalls.

Frequently asked questions

Is a “likely OK” fit street-legal?: This tool does not certify legality. Wrong load/speed ratings or rubbing arches are still failures. Ask a tyre fitter.
Where is the DOT code?: On the sidewall, often near “DOT”. The last four digits of the complete code are week and year of manufacture.
Can I mix sizes front and rear?: Only if the manufacturer specifies a staggered setup (common on performance cars). Do not invent your own staggered fitment.

Related tools and guides

MotorTools calculators give planning estimates only. Confirm figures against GOV.UK, your V5C, handbook or a qualified garage before buying, renewing tax or carrying out work.