Arrangement applied to an envelope for retreading tyres

An envelope for tire retreading in which a tire carcass is covered by a pre-molded tread having a top with a certain standard of grooves, the envelope being comprised of two parts, the first part having a sidewall from which extends a flap, the sidewall having a form that is able to cover at least part of an external portion of a first side of the carcass and a first shoulder of the tread, and the flap having a form that is able to cover at least part of the top of the tread;

• and the second part having a sidewall from which extends a flap, the sidewall having a form able to cover at least part of an external portion of a second side of the carcass and a second shoulder of the tread, and the flap having a form that is able to cover a remaining part of the top of the tread;
• wherein an end region of the flap of the first part is covered by an end region of the flap of the second part in order to form an overlapping joint;
• and at least one of the parts of the envelope having an air valve, wherein a free end of the flap of the first part has at least one differentiated cross section whose thickness is greater than the thickness of a remainder of the flap of the first part, wherein the free end and the remainder of the flap of the first part have an inner surface able to be entirely in contact with the at least part of the top of the tread, wherein a free end of the flap of the second part has at least one differentiated cross section whose thickness is greater than the thickness of a remainder of the flap of the second part, wherein the second part is identical in shape and size to the first part, and wherein the overlapping joint is covered by an elastic ring that is wide enough to cover the differentiated cross section of the first part.