Rubber wedges--old tire?

[JohnV]

There's a big old tractor tire washed up on the shore near me, with fat, thick bar treads. I keep thinking I should saw off some of the bar treads and shape them into mast wedges. I researched a little and found that store-bought wedges are a harder grade of rubber than typical tire rubber, but I don't know whether that difference is significant.
For me, making my own gear for the boat is half the fun of owning it, but it still has to work.
Any thoughts on this?
PS I'm still figuring out how to get the tire off the shore and off to a dump but that's a different project.