I have a 4mm optional chassis for my r40 and it didn't care for parking lot style tracks. So I put the standard chassis back on. Worked fine. Experiment 2 was that I ran the stiff chassis on 301's track after they raced and the stiff worked better. I'm gonna run my 720 on the same style track as I run the 960. It's just my observation that the smoother and faster the surface, the stiffer the chassis should be. It just feels like it to me.. (somebody correct me if I'm wrong)
P.S. I will install my blade swaybar.