Are arch extensions legal in United Kingdom?

Conditional. A legal way to cover a wider track. Mudguards must cover the full width of the tyre tread. The extension must be securely fitted, without sharp edges or dangerous protrusion.

Are arch extensions legal in United States?

Legal. Legal to fit in every state. Several states require the tread to be covered by the fender or flare. Flares must be securely mounted with no sharp edges, and very wide setups can hit state width limits.

Are arch extensions legal in Germany?

Conditional. ABE or certificate plus change inspection. Wheels need effective covering of the tread. Universal extensions without test documentation end up at individual inspection, and edges must be rounded and firmly mounted.

Cross-jurisdiction

Arch extensions and fender flares: UK vs US vs Germany

Flares exist to solve a legal problem rather than create one: they are how a wider track stays inside the coverage rules.

By Brandon · Sources last reviewed July 2026.

The verdict is not the same in all three markets, so the column that matters to you depends on where the car is registered.

Market	Verdict	The rule that decides it
United Kingdom DVSA / GOV.UK	Conditional	A legal way to cover a wider track Mudguards must cover the full width of the tyre tread. The extension must be securely fitted, without sharp edges or dangerous protrusion. Full UK guide →
United States EPA, NHTSA and state codes	Legal	Legal to fit in every state Several states require the tread to be covered by the fender or flare. Flares must be securely mounted with no sharp edges, and very wide setups can hit state width limits. Full US guide →
Germany StVZO / KBA	Conditional	ABE or certificate plus change inspection Wheels need effective covering of the tread. Universal extensions without test documentation end up at individual inspection, and edges must be rounded and firmly mounted. Full Germany guide →

What the split actually means

The US is outright legal because flares are the remedy, not the offence. Germany still wants the extension itself approved, since it is a body part.

Why the answers differ

Are arch extensions legal?

Flares are unusual in this dataset because they exist to solve a legal problem rather than create one. Every market requires the tyre tread to be covered, and a flare is how a wider track stays legal, which is why the US verdict is outright legal in every state. The UK reaches the same conclusion, treating extensions as a legitimate way to cover a wider track provided they are securely fitted and free of sharp edges. Germany agrees on the function but still treats the extension as a body part needing approval, so universal extensions without test documentation end up at individual inspection. All three add the pedestrian-safety condition that rounded edges and secure mounting matter, and the US notes that very wide setups can hit overall width limits.

Verdict at a glance

The same three markets, grouped by where they land.

Legal

United States. No approval step and no conditions worth planning around in this market.

Conditional

United Kingdom and Germany. Permitted, but only once the condition in the table above is met.

Sources

Primary legislation and regulator guidance behind each market's verdict.

Other cross-market comparisons

This is a comparison of national rules, not legal advice for your vehicle. Rules change, and the US row in particular summarises federal law where one exists and the common pattern across states where it does not. Confirm the position in your own state or region before you buy or fit anything. Sources last reviewed July 2026.