Are Towing Mirrors Legal in the US?

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Towing (extended) mirrors are legal in the US, and in many states they are required when you tow something wide enough to block your standard mirrors. The rule is about having an adequate view to the rear, not the mirrors themselves.

Why?

State law requires a driver to have a clear rearward view, usually defined as being able to see a set distance behind the vehicle. When a trailer, camper or wide load blocks the factory mirrors, extended towing mirrors are how you meet that requirement, and a number of states specifically mandate them for wide towing.

The mirrors have to be securely mounted and actually deliver that rearward view. Clip-on or bolt-on towing mirrors are fine as long as they are stable and correctly adjusted.

So towing mirrors are road-legal and often required while towing. When you are not towing, mirrors that extend the vehicle's width are generally meant to be folded in or removed, since running unnecessarily wide mirrors is its own issue.

What decides if it's legal

The driver must have an adequate view to the rear of the vehicle and trailer.
Many states require extended mirrors when a trailer or load blocks the standard mirrors.
The mirrors must be secure and give a clear rearward view.
They should be folded or removed when not towing if they extend the width.

Does it depend on your state?

Yes. Whether extended mirrors are required, and the exact rearward-view distance, is set by state law and depends on what you are towing. The general need for an adequate rear view applies everywhere.

Related legality guides

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Sources

This page is general guidance, not legal advice, on the rules in the US for towing mirrors. The detail varies by exact vehicle and changes over time - confirm with your insurer and the EPA, NHTSA and your state DMV before modifying.