FWIW, I had BST Rapid Teks on my VR4 track bike. Noticed a difference between them and the stock forged rims in that once the BSTs were mounted, the bike was over damped. The lower unsprung weight allowed for less rebound damping which made the bike more compliant which is probably more of a benefit on the road than on a smooth track to be honest. The "downside" of the BST wheels (or any lightweight wheel) is that you reduce the moment of intertia and gyroscopic effects that would otherwise keep the bike stable (and pointing straight) at higher rotational speeds. For a large liter bike that is ridden in a more point-and-shoot manner, I'd argue that the bike can feel a bit more flighty with very light rims. At least for me, it felt more like a change than an outright improvement. Of course, I'm no professional racer and I'm sure a truly latented rifer will be able to take advantage of the added nimbleness without getting spooked by the lesser stability.
On the road, however, the effects of the BST wheels were more obvious and universally appreciated. More suspension compliance and better bump absorption (due to being able to run less fork and shock damping. Which made the bike more stable over mid corner bumps. With more time spent in the lower gears, the rate of acceleration due to lower MOI, resulted in more effortless acceleration (limited by TC/traction of course). Bike just felt lighter in all respect which was a great thing. The flightiness felt on the track wasn't reproduced on the road due to the lower speeds and lesser lean lean angles. And all these differences were abundantly noticeable on the V4R which already had reasonably light forged rims. I did the same test on my KTM Superduke which came stock with heavy cast boat anchors for wheels. And the difference was truly profound. Even more obvious than the effects I felt on my Duc.
