That is going to be hard if you want to adapt what you have already modelled. You could start the wheel again, model a portion of the wheel with that tyre tread, then duplicate along a circle curve with an array. If you want to do it more easily then why don’t divide the mesh a few more times and apply the image as a displacement?
yer the tire in the pictures ive already posted are just place holders and i have been using the technique you mentioned…using the displacement modifier might work…hmmm i shall investigate.
[edit] ive done a test displace and it works…but its pixelated and doesn’t match when you add an array…also its very dense [edit]
Add a subsurf before the displacement. It needs lots of verts to work. And move the array to the top of the stack.
thanks for the tip 
Love the detail on those wheels 
there is a lot of detail lol…i wanted to make something for once which is detailed and can really improve my modelling abilities