Why tubeless?

December 5, 2006 at 5:39 am Leave a comment

Can you believe that there was a time when every tyre had a tube in it! Punctures were frequent, and to ‘pinch the tube’ when fitting the tyre was common. It still happens with bicycle tyres. They need airtight rims to be tubeless. Nowadays practically the only time a motor tube is fitted is when an off-roader has a puncture, hasn’t the gear to inflate a tubeless tyre, and goes to the toolkit to fit the spare tube which an experienced off-roader always carries.

The most graphic way to illustrate the benefits of a tubeless tyre, is to inflate a party balloon. Stick a strip of masking tape to the balloon, and pierce it with a pin. The balloon goes down, but slowly. Now prick it away from the strip, and it goes ‘bang’. The balloon surface is not under tension to the same extent under the strip of tape.

In other words, a puncture in a tubeless tyre gives a ‘slowout’ not a ‘blowout’, gaining in safety and reliability. Indeed, depending on where the tyre is punctured, you may only notice an annoying slow leak before you wake up to the cause. Often, you can hear the puncturing object hitting the road, before you realise that is causing you problems.

To discard the tube was a revolutionary modification to the way tyres were serviced. Previously anyone with a small compressor could fit a tyre and tube assembly. However, a tubeless tyre requires a high volume blast of air injected into the tyre interior, to force the beads out of the wheel well onto the bead ledges, and seal. The tyre-fitting machine incorporates this into its design, so that fitting tubeless requires a reservoir of air and a fitting machine, taking it out of reach of the handyman. Once the beads are seated, it is a different matter.

Early tubeless tyres struck problems. Air that leaked into the casing could gather at a particular spot, and cause a bubble to develop. Rubber itself is permeable to air, so the design incorporates a relatively thick layer of rubber (the tubeless liner) on the interior surface of the tyre. The inside of the bead area has to be sealed too, and exposure of the casing cords due to tearing of the bead toe during fitting can leak air into the casing. That’s why the tyre levers used have no burrs, and a lubricant is used on the beads.

Big improvements have been made in the compounds bonding the layers of rubber and casing cord reinforcement over the years as well. The adhesives used to bond the rubber to the plies are quite sophisticated, because they have to be flexible and long lasting, over the life of the heat prone tyre.

The type of valve used with a tubeless tyre snaps into the hole in the rim, under compression, to maintain the seal. Tubes could retract their valve stem into the interior of the tyre when the tube deflated, and ruin the casing. With tubeless, provided you change the tyre before the sidewall is damaged from being run flat, there is a good chance that the tyre is capable of being returned to service. It should always be examined INSIDE after a puncture.  If the serviceman recommends that you fit a tube to your punctured tyre, you should realise that you are robbing yourself of the many benefits that a tubeless tyre bestows.

However, when a tyre is punctured in an area that cannot be repaired with a tubeless repair satisfactorily, then it is an option to fit a tube, albeit an expensive one. There are limitations to which part of the tyre can be repaired. The shoulder-buttress area where extensive flexing takes place is such an area.

Entry filed under: Tyre Technology. Tags: , , .

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