I was on MTBR in the Spec SJ 6Fattie forum and saw a post about various suspension designs that I thought I'd repost here.
"Oh boy. I'll try to keep this short and simple and probably over-generalized, but if you google anti-squat, you will have the opportunity to go down a rabbit hole from which you need never emerge. I'm sure somebody will jump in to disagree or put a finer point on things, but I can tell you what I was thinking in saying that.
The Stumpjumper suspension is designed with less of an emphasis on inhibiting compression of the shock under pedaling forces than some other suspension designs. In general, modern bikes, are designed such that the force exerted by the chain on the rear triangle counteract the natural tendency of the suspension to compress during acceleration. Earlier designs of many bikes, including the FSR suspension platform used by Specialized, did not do this as well and, thus, significant portions of pedaling energy were wasted on movement of the suspension, rather than on moving the bike forward.
In recent years, the FSR suspension platform used by Specialized and others has been designed to achieve 100% anti-squat (pedaling forces exactly counteract the tendency of suspension to compress) when the bike is near its neutral sag point under rider weight, However, other suspension platforms, like Santa Cruz's VPP and DW Link designs, maintain that 100% anti-squat throughout the upper half of the bike's travel. (In the lower half of the travel, the rider is presumably charging downhill and the suspension absorbing bigger hits, and thus pedaling efficiency is not as big a factor.)
The FSR (as well as single pivot and split pivot) designs have relatively linear falling anti-squat rates, where the pedals offer progressively less resistance to suspension compression, the more the suspension compresses. A falling anti-squat rate results in less efficient pedaling compared to VPP designs (a generalized term including Santa Cruz, DW Link, and others) in situations where the suspension is compressed, such as when pedaling over rough terrain or when standing and mashing on the pedals. On the SJ, the anti-squat falls at a rate that is faster than that of competing bikes, like the Cannondale Bad Habit (a single pivot) and DeVinci Marshall (a split pivot). Thus, there are many bikes that pedal more efficiently than the SJ.
There are trade-offs to this greater efficiency, and in previous versions of suspension designs that emphasized anti-squat, those trade-offs often gave-up a lot in suspension performance. One trade-off for this loss of efficiency is that because pedaling forces do not resist compression of the shock as much, the shock is free to respond to bumps when pedaling, and thus traction is optimized. Also, because pedaling does not resist suspension compression as much, the pedals are less likely to kickback when an obstacle is encountered that forces the shock to compress, as on suspension systems emphasizing anti-squat behavior. The degree to which each of these trade-offs (and others) is an issue varies with the specific design. These trade-offs were much more problematic when anti-squat levels much greater than 100% were incorporated into some suspension designs, but there are definitely characteristics of each design that annoy or appeal to different people riding different terrain.
The way that I perceive these differences is that the FSR suspension is more plush and responsive and, in some cases, provides better traction than some of the VPP designs. The advantages of the FSR platform are diminishing as VPP designs get better, however, while internal shock damping performance has also improved, allowing for the inefficiencies of the FSR and other similarly sensitive platforms to be compensated somewhat. That said, were I to be buying a bike now, I'd likely get something with a more efficient pedaling design, as I prefer the firm pedaling platform and not having to worry about flipping the compression damping mode switch on my shock. YMMV"
From my limited experience with FS bikes, it seemed to me the OP knew at least a bit about what he is talking about.
