The theory is that the beam bikes isolate you from much of the road shock of standard bikes and having ridden and raced a Softride Solo for a number of years I can say that this is indeed the case. The extention of that is your question - will this help you run faster. Again, in theory this should be the case, but from my direct experience I can't quantitativly say that riding on the Softride made my run splits faster.
One observation that I can make is that the harder you go ie the more force you appply to the pedals via your legs the less force you are actually applying to the saddle and the closer a beam bike comes to a standard bike in how it feels. My anecdotal onservation would be that for long easy rides, the beam does have a positive impact on how your body feels after the ride. You feel better. But after a hard 40K, 90K or 180K effort at race intensities, if you are really going for it, I can't really say that I felt "better".
Just some thoughts.
Steve Fleck @stevefleck | Blog