The bet that Petruchio makes with his friends comes in the final scene of the play, Act V scene 2, and seems to be organised by him to demonstrate his final mastery of Katharina, his wife, and his success in "taming the shrew" that he has taken on. Notice how, when Petruchio makes his bet, he is swift to force Lucentio to raise the wager to 100 crowns which serves to increase the suspense.
Then, of course, a major way in which suspense is built is the order of the wives who are called to attend their husbands: Bianca is called first, followed by Hortensio's wife with finally Petruchio's "shrew" being summoned. From what we know of the characters of Bianca, the widow and Katharina, we would expect Katharina to be the most likely to disobey her husbands proposal. Thus seeing the other two wives do this before Katharina really serves to raise suspense in both us and the characters on stage. Note how Hortensio, whilst Petruchio's servant is summoning Katharina, predicts (incorrectly) that she will not come.
Thus it is that suspense is raised concerning this bet by the wager being increased and the order in which the wives are summoned, with Katharina being left until last.