You can go down one tongue size, but with a size 30 you couldn use the smallest tongue. Thre is some wiggle room, the front or bottom part of the tongue just isnt as long, but the metal clips they use to attach slide and provide some iggle room so they just slid back. In your particular case, with size 29.5's these particular tongues will work, thats the size I have on my 31's. It is a little small but you wont notice a difference when you are skiing