It can be run as a rubber car if you change your springs and all but the chassi will work. It doen't have to torsional flex most of the newer cars have but that doesn't seem to affect anything. I ran the RDX Phi and it had the foam tire chassi in a rubber tire class and was very competative.
I'm pretty sure my RDX is a foam chassis, but I run it in Stock Sedan on rubber tires with very good results. I used to race it in VTA before I stepped up to the sedan class.
I'm pretty sure there are still upper decks of different thickness available if you're concerned about the chassis having too much torsional rigidity. I haven't gone that route yet, I've simply experimented with how snug or tight the upper deck screws are to the bulkheads - you can vary the amount flex depending on how tight those screws are.
Enjoy your RDX, they are on par with every hight end touring car being made to this very day.
I've seen a few foam cars converted to rubber w/ success.
put 3 or 4 degree castor blocks on, slap on 12.5 or 14lb rear springs, and 19lb fronts and run it.
+1. We have a few people, myself included running converted foam chassis. Just need to soften the suspension up get the right caster blocks and you should have a fine car. If your car has a one way or diff up front you may want to invest in a spool or tighten the diff down. That seems to be the ticket for rubber tire on carpet these days.