A retread is a tire whose old, worn tread has been mechanically buffed off and replaced with a new layer of rubber on the original casing. It's a different thing from a used tire — and people regularly confuse them.
How retreads are made
The original casing — sidewalls, bead, internal cords — is inspected with high-pressure leak detection and X-ray imaging. If sound, the old tread is buffed away. New tread is bonded on under heat and pressure, similar to vulcanizing. The result is a tire with a new tread face on an existing casing.
Where retreads make sense
Retreading is enormous in commercial trucking. A semi tire costs $500+ new. A retread costs $200 and on a fleet truck running 100,000 miles a year, the savings are huge. Tire casings on commercial trucks are engineered for multiple retread cycles.
Aircraft tires are also retreaded heavily — sometimes a dozen times each — for the same reasons.
Where retreads don't make sense
Passenger-car tires are rarely retreaded today. The economics don't work — a new passenger tire is cheap enough that the labor cost of retreading approaches the price of new. And passenger casings aren't built for multiple service lives the way truck casings are.
Don't confuse a retread with a used tire. A used tire is one that came off a vehicle with tread still on it — never modified, just cleaned and inspected. A retread is a manufactured product.
Are retreads safe?
Well-made commercial retreads from major manufacturers (Bridgestone Bandag, Michelin Recamic, etc.) are safe and perform within a few percent of new tires. Bargain-basement retreads from unknown sources are a different story — failure rates are higher and the casings may be marginal.
The famous highway-debris myth
Many drivers blame retreads for the rubber chunks they see on highways ('alligators'). Studies by the NHTSA found that most of these come from underinflated tires of any kind — new and retread — not specifically from retread failures. Pressure neglect, not retread quality, is the leading cause.
Used vs retread for your car
For passenger and light truck use, a quality used premium tire beats a cheap retread on almost every metric: cost, performance, ride, and tread life. Save retreads for commercial vehicles.
Retreads are a commercial-truck story, not a passenger-car one.