nearby for some testing. I hear you on that. The NBR kinda works both ways because of it's length I think. Being so long and so often used for testing means a low time stands out but yeah, it does make getting that low time or accurate time difficult for exactly the reasons you said. Just one slow 3-series Bimmer or some tourist taking a bad line and it can be an issue.
I'm not sure what they did with the GT-R or will do for something like the ZR1 (if anything at all) but hopefully they'd give it a handful of runs on a clear day to minimize those issues. If only TG got big enough that all manufacturers used their track ;)
