26 March 1999

Michelin guide to puncture repairs

By Andy Collings

OUR tubeless tyre feature in last weeks issue (Tyres and Wheels special p 72) prompted Michelin to make some interesting comments – particularly in the puncture department.

The company says the introduction of tubeless tyres has resulted in punctures being less urgent problems when they occur. In many cases the penetrating object, if it stays in place, prevents most of or all of the air escaping.

A tubed tyre, on the other hand, goes down rapidly when it is punctured because the tube under tension, tears away from the point of penetration.

Michelin also says the increasing use of low profile tyres has made the use of tubes less satisfactory because of the risk of air becoming trapped between the tube and tyre during inflation. This is also true for most other tyre products and many problems have been caused by attempts to put tubes of incorrect size and shape into low aspect tyres.

Trapped air also increases the risk of damage by chaffing of tyre against tube due to the components not being in close contact.

Repair of a puncture in a tubeless assembly by fitting a tube is not considered to be good practice. Besides being expensive, the benefits of the tubeless concept is lost. If the tyre is radial, with steel bracing, it is possible for the new tube to be damaged by the tyre fabric which was pushed into the tyre when it was punctured.

And now for the matter of actual puncture repair in tubeless tyres. Repair, says Michelin, cannot be achieved satisfactorily unless the tyre is removed from the rim. It points out that there may be much more damage inside the tyre than can be seen on the exterior – a problem which might manifest itself as a catastrophic event sometime in the future.

External plugging is at best a "get-you-home" solution. The recommended patch for this purpose has a mushroom head on the inside which minimises the risk of air infiltration from the area of repair into the tyre casing which could result in separation of the tyre fabrics. &#42