The Catalan original has:Tirant lo Blanc chapter 71 (b) wrote:Unnerved by the two blows, Tirant struck him again in the same spot, snapping the piece of leather that held his straps in place. The knight's rerebrace was tied to his arm by a thick silk cord, and the straps held firm because they were raw hemp. Though the rerebrace stayed on his arm, it was too loose to protect him, and thus they fought many passes, one with his right rerebrace damaged and the other with his left one."
Edit: here is a photo of this passage in the edition of 1490 tirant-lo-blank-ch-71b-malfunction-full-hl-scaled.jpgE alaltra
carrera que feren Tirant lo torna
ha encontrar en aquell guardabraç:
e rompe lo cuyro per hon passen
les tiretes: e tenia lo guardabraç li
guat de parte de dins ab vna corda
de seda tan grossa com lo dit: e les
tiretes nos pogueren rompre: per
que eren de cor de canem cruu: e lo
guardabraç li fora del tot caygut si
no per lo cordo de seda: e daltra part
li daua gran enpediment: perque
dalt era desset que pochvtil li fehia
E ari feren moltes carreres: que al
hu fallia lo guardabraç dret: e alal
tre lo esquerre.
Edit: you can find a Spanish translation of this scene in Joanot Martorell and Martí Joan de Galba (tr.) Tirant lo Blanc. 2 volumes (El Libro de Bolsillo: Alianza Editorial, Madrid, 1969) vol.1 p. 183
So Tirant struck his opponent in the left guardabraç, and broke lo cuyro through which pass les tiretes (Spanish tirillas); the guardbrace was held by a corda de seda tan grossa com lo dit; the thing which held was de canem cruu (Spanish de cáñamo crudo) ...
What do you folks think happened? Did the arming tab on the pauldron tear but the strap around the triceps hold? Ken M. thinks the lance might have hit the upper cannon of the bracer (what some curators call the rerebrace) and burst the points at its top end.
Edit 2021-10-30: This dictionary of Catalan has
tireta
1 1 f. [LC] Tira estreta. (narrow band / strip)
1 2 f. [LC] [ED] Cordó o tira estreta capçada amb llauna o filferro, usada per a cordar gipons o altres peces.
2 f. [IMI] [ED] Peça estreta de pell que, posada a la part posterior de la sabata, serveix per a reforçar la unió de les dues peces que formen la talonera.