By Sophia ReedAirless metallic tire technology originally engineered to carry robotic rovers across the jagged craters of Mars is transitioning to everyday terrestrial cycling. Developed through a space agency commercialization partnership, the METL bicycle tire replaces pressurized inner tubes with a woven radial mesh of superelastic nickel-titanium that never punctures or goes flat.
From Damaged Martian Wheels to Superelastic Spring Mesh
Designing wheels for planetary exploration presents extreme mechanical challenges because inflatable rubber degrades rapidly in vacuum and freezes solid at minus 100 degrees Celsius. Early Apollo lunar rovers relied on woven piano-wire steel mesh, while the Curiosity Mars rover used rigid machined aluminum wheels to support its nearly one-ton chassis. However, after sharp, cemented Martian sandstone punctured and cracked Curiosity’s aluminum treads, materials engineers at the Glenn Research Center sought a metallic structure that could deform over sharp rocks without suffering permanent plastic bending.
Their solution replaced conventional spring steel with an interlocking radial weave of NiTinol, a stoichiometric alloy composed of roughly equal atomic parts of nickel and titanium. While standard spring steel can stretch by less than one percent before yielding permanently, superelastic NiTinol can endure reversible strains of up to eight to ten percent—roughly thirty times the elastic deformation of ordinary steel. A rover tire woven from this alloy can flatten right down to the axle over a jagged boulder and snap back to its exact original circular shape.
Atomic Phase Transitions Inside Nickel-Titanium Wire
Unlike conventional airless polymer tires that rely on heavy cellular foam or rigid plastic spokes, a shape-memory alloy tire absorbs impacts through a reversible solid-state phase transition at the molecular level. At normal operating temperatures and resting loads, the nickel-titanium atoms arrange themselves in a symmetric cubic crystal lattice known as the austenite phase. When the wheel rolls over an obstacle or supports a rider’s weight, mechanical stress triggers an instantaneous, diffusionless shift into a more flexible monoclinic crystal structure called martensite.
Because this stress-induced martensitic transformation occurs through coordinated atomic shear rather than the breaking and slipping of metallic bonds, the wire does not suffer metal fatigue like ordinary steel springs. The moment the wheel rotates past the bump and mechanical load drops, the crystal lattice automatically reverts to the rigid austenite phase, releasing stored elastic energy with minimal rolling resistance. By tuning the alloy composition and thermal processing profiles, engineers can calibrate the exact radial stiffness of the metallic carcass to mimic specific road or gravel inflation pressures.
Commercializing METL Tires for Cycling and Micromobility
Through a space technology startup licensing initiative, The SMART Tire Company adapted this radial mesh architecture into the consumer METL bicycle tire. The production design encases a lightweight, gold-or-silver-anodized NiTinol wire core inside a replaceable poly-rubber outer tread that provides dependable wet and dry cornering grip. Because the metallic lattice lasts for the entire operational lifespan of the bicycle, riders only need to retread the thin outer rubber casing after thousands of miles, cutting rubber waste by roughly half compared to disposable pneumatic tires.
Eliminating pressurized air also removes the threat of roadside flats, rim pinch punctures, and messy liquid sealant maintenance for daily commuters, bikepackers, and electric delivery fleets. As manufacturing scales up across advanced materials and mobility engineering, developers are testing heavier-duty shape-memory radial tires for electric scooters, commercial transport trucks, and upcoming crewed lunar terrain vehicles.
