I have installed JConcepts 8th scale buggy foams in my SCT Goosebumps. What I can say is that the form of the tire is different which seems to effect the contact patch of the tire. Using them on carpet has been fantastic as long as I keep them from drying out.

I have not run them with the stock foams. The 8th scale foams have a wider form facter. They also crown the surface and control inertial growth of the tire when at high revs.

I was using this set-up on hard bumpy clay with loose surface dirt. They were not optimal for that surface. A softer insert would probably be better. I will be trying other tires this weekend.