Silca has launched a range of three TPU inner tubes. That’s despite Josh Poertner, Silca’s boss, previously having had bad experiences with the ultra-light tubes.
Poertner says he put his whole family's bikes on orange TPU tubes from an unnamed brand a few years ago, but because the valve stems are narrower than standard ones, and unthreaded they’re difficult to engage with a pump.
Within six months, all the tubes failed at the junction between the valve and the tube, he explained.
We've also had bad experiences with TPU tubes, with Jack Luke rating them his worst upgrade.
Poertner delved further and found that dyes in the TPU could reduce their strength. “The dyes can reduce the peak elongation, they can reduce the ultimate tensile strength and the yield strength of the material,” he says. They can also increase rolling resistance, Poertner claims.
Therefore, the Silca Ultimate TPU inner tubes are made in Germany using undyed thermoplastic polyurethane. Silca is not the only brand to make undyed TPU tubes: Continental, Schwalbe and Vittoria, for example, all sell undyed TPU tubes.
Lower weight and rolling resistance
TPU inner tubes offer lower weight and a more compact size than a traditional butyl inner tube, plus they’re more air-tight than latex tubes, so you don’t need to pump them up before every ride.
Rolling resistance is usually lower than butyl tubes, too, although bicyclerollingresistance.com, testing a range of brands of inner tubes, has found them in general to be slightly less free-rolling than latex tubes.
Nevertheless, Silca claims a rolling resistance reduction of between 2 and 4 watts versus a butyl tube and that its tubes are only 0.2 watts slower than latex.
Designed to address weak points
TPU tubes tend to have two weak points, depending on how they’re made: the valve stem can break if it’s made of plastic rather than metal, and the tube can fail at the junction between the valve and the tube.
Silca has a patented bonding system between its aluminium valve and the tube, which uses two aluminium flanges to sandwich the TPU, with a rubber gasket on top to protect the tube around the valve drilling in the rim. Poertner claims many brands use a plastic one-sided flange, even with a metal valve.
It also uses a threaded valve with a locking nut to avoid tube failure due to movement and friction when pumping by hand. The valve has a removable core, making it compatible with valve extenders.
The Silca TPU tubes are also claimed to be heat resistant, so they’re suitable to use with an electric pump, although Silca recommends inflating in 15psi steps to avoid overheating. Some TPU tubes are not recommended for use in rim-brake wheels, but Silca’s tubes are rated for both disc-brake and rim-brake wheels.
Most TPU tubes are glued together along their length, which can also cause failure. Poertner says Silca’s tubes are friction-welded with a turned-back overlap between the two sides, while many tubes are only glued with a flat overlap.
“The joint is guaranteed air-tight and the tubes are 100% tested at the factory,” Poertner says. “It’s significantly stronger and has significantly higher elongation before failure. That’s what allows us to have two sizes of tube in a space where others might have three or four sizes of tube.”
Silca packages its TPU tubes with an alcohol wipe and an adhesive repair patch, so if you are unlucky enough to puncture twice on a ride, you’ve still got the means to repair the tube.
The Silca Ultimate TPU inner tube is available in two widths, covering a wide range of tyre sizes: 24-43mm and 44-64mm. The narrower tube is sold with either a 50mm valve, with a 44g claimed weight, or a 70mm valve with a 45g claimed weight.
The wider tube comes with a 50mm valve only and weighing a claimed 64g. All are priced at £39 / $39 each.
