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Show GUARD AGAINST STONE BRUISES This Form of Injury to Tires Is One of Most Common and Expensive to Owner. BREAK i:J FABRIC IS INSIDE Inexperienced Driver Who Gets Hard Bump Against Corb or Any Other Object Usually Looks for In-Jury In-Jury wn the Outside. A "sfone bruise" is the term used to describe an injury to a tire caused by striking some object with sufficient foDce to cause the tire fabric to be broken. It need not be a stone that causes the damage. The break In the fabric may be in only one ply or it may be in all of them ; but in any case It is always the Inside ply that breaks first. An inexperienced driver whose tire gets a heavy blow from a stone or a curb usually looks over the outside of the tire to see if any damage has been Bump Against Curb Will Cause "Stone Bruise." done. But the old driver knows that If harm has been done the place to look for it is in the Inside and that any break In the fabric will be registered on the Inside ply first. Inside Ply Shorter. Normally the inside ply Is shorter than the rest and each ply is shorter than any of the others which are located lo-cated outside of it. This is because it is on the inside of the curvature of the tire. Now if the tire is suddenly compressed com-pressed at some point to a considerable extent, such as shown In the illustration, illustra-tion, the relative position of the plies is reversed ; that is, the ouside ply becomes, at this particular point, the Inside ply as regards the curvature and the inside ply becomes the outside ply as regards curvature. If it should happen, as it often does, that only one or two inner plies are broken, therewill not be any signs of the injury on the outside until a considerable con-siderable time afterward. This Is because be-cause the other plies still unbroken will continue to hold against the air pressure pres-sure even though they will be under excessive strain. But continued flexing flex-ing will eventually break them also, and the result may be a blowout, which may occur at any time, even on a perfectly per-fectly smooth pavement. Other Effects. Another effect of a break In one or two Inner plies may be that from continued con-tinued bending the broken edges of the fabric rub a hole in the inner tube at that point. Sometimes the break is so pronounced, especially in a fabric tire, that the air pressure forces the lnnet tube into the break, and as this is continually con-tinually closing and opening, as the tire rolls, the action is like a pair of pinchers and cuts he tube. If the tube is chafed through or cut after a bruise, such as described, the air will pass directly through the carcass car-cass and force the rubber side covering, cover-ing, and sometimes the tread, loose from the fabric. When this happens the user generally terms it a blowout, and as a mutter of fact it Is ; but, contrary con-trary to the opinion often held, It is seldom the result rf a defect in manufacture. manu-facture. It can generally be traced to an Injury sustained some time prior to the final breaking down of the tire. |