To be completely flexible with when to hide and show the tabs, you can also just use a CSS class like the following:
ion-tabs.hidden div.tabbar {
display: none
}
In your tabs.ts you can have a boolean variable to denote if the tabs should be hidden.
public hideTabs:boolean = false;
In tabs.html add ngClass to ion-tabs to apply the hideTabs style when the variable is true:
<ion-tabs [ngClass]="{'hidden': hideTabs}">
You can toggle the hideTabs variable in any function f.e. inside the function that navigates to a subpage, but also in ionic's ionViewWillEnter() functions.