Surly TPU Tube - 24 x 6.2 48mm Presta ValveSurly TPU Tube 24 x 6. 2 48mm Presta Valve. The Surly TPU or Thermoplastic Urethane tube is a tough airtight material lighter than traditional butyl innertubes. It is designed exclusively for the Surly Molenda tire and allowed for a custom oversized 6. 2" width that maintains its structure even when operating at low pressures. With the TPU tube installed you can air down your Molenda tire to maximize contact patch for better flotation traction and