I got some really short valve stems from; http://www.patchboy.com
I think there around 3/4" long. I like using the shortest valve stems so there out of the way from getting hit with sticks when i'm in the brush.
3/4" valve stems TR#412 rubber snap in #17-412 50 for $13.50
Using this short stem allows you to use the wide frame cub cadet rims turned around on the narrow frame spindles.