They are nylon but it was a bad landing. I wouldn't expect anything to have survived that. I was carrying speed to and it landed square on the wheel, so it took all the impact.
My last bashing session I ragged the car around badly and nothing gave way, so I'm very impressed with the quality. There was an original HPI 5b ss converted to sc that also broke a few things today, so I suppose it could happen to anyone on any car.
I managed to get a cheap set of KM monster tyres, so now I have one spare when I'm out of luck with them I'll go for the hostiles.
If you would like me to post the broken rear 5b tyre+rim so you could size it up let me know. Will be free of charge.