Inner tubes were the standard fitment for the original wire-wheel-equipped classic MGs and for the earlier steel-wheel applications before the tubeless construction became universal in the late 1960s. Modern tubeless wire wheels do not need inner tubes, the rim is sealed against the spokes during manufacture, but the original wire-wheel cars and several specific classic-MG applications still need a tubed fitment, and the Wheel Tubes section gathers the inner tubes in the diameters and patterns required.
Natural and Butyl Rubber Construction
Inner tubes are produced in two principal rubber specifications. Natural rubber tubes are the original specification, the rubber compound used through the original production years, with the visual appearance and the slight permeability characteristic of the natural-rubber compound. Natural rubber tubes are the period-correct choice for concours restoration work where the original specification matters. Butyl rubber tubes are the modern alternative, a synthetic rubber with substantially lower air permeability than natural rubber (so the tyre holds its pressure longer between top-ups), better aging resistance, and longer service life.
Butyl tubes are the practical choice for owners running cars on a daily-driver or weekend-touring basis where the lower maintenance is worth the small departure from period specification.
Sizes and Application
Inner tubes are stocked in the sizes used across the classic-MG and wider British classic range, sized to the tyre diameter and width fitted to the wheel. Common applications include 145/155 x 13 for the Midget on its original specification, 165 x 14 for the MGB on its original specification, and the various other sizes used across the MGA, MGC and MGB GT V8 range. The valve pattern is matched to the rim, typically a TR-13 or TR-15 short-stem pattern for most applications, with longer-stem variants available where the rim design or the wheel-arch clearance requires it. The tube is sized slightly smaller than the tyre's inflated internal volume, allowing it to inflate snugly into the tyre without being stretched beyond its design limits.
Fitting and Care
Inner tube fitting requires care during tyre fitting, the tube is positioned inside the tyre with the valve aligned to its hole in the rim, the tube is partially inflated to give it shape, and the tyre is then mounted onto the rim with the tube in position. Care during fitting prevents the tube being pinched between the bead of the tyre and the rim edge, a pinched tube will fail within minutes of the tyre being inflated to road pressure. After fitting, the tyre is inflated to road pressure and the tube settles into its operating position. Wire wheels with inner tubes also need a rim band, the protective strip of cotton or rubber that fits inside the rim, covering the spoke nipple heads so they cannot puncture the tube.
A missing or perished rim band is one of the most common reasons for inner-tube failure on wire-wheel applications, and the rim band should always be inspected and renewed at the same time as the tube. For owners with tubeless wire wheels, neither the inner tube nor the rim band is needed, the wheel is built to run tubeless and the supporting items are for tubed fitments only.