The rear axle path tangent will determine how the suspension will react to pedaling at any given moment. This means that, neglecting friction in the mechanism, each particular geometry will have its maximum effectiveness only in certain “ideal” gears (from a practical standpoint, this could mean one gear or several). The further the gearing from ideal, the more reactive any suspension geometry will be.
For a given deviation away from ideal gearing, “suspension rate” (spring stiffening) will determine the amount of reaction from a pedal stroke. Shorter travel suspensions tend to be less reactive to pedaling then longer travel versions, since short travel designs should have higher, more rising rates. However, the difference between linear and rising rates will be small in the shallow regions of travel where pedaling is affected. In practice, the actual rates in these shallow regions will largely be a function of the total travel, or rear axle path length.
It is common these days for designers to take into account the slight tendency of a bike to fold or “squat” under acceleration. To do this, one adjusts the rear axle path so as to increase, by some significant amount, the distance of the rear axle from the bottom bracket (BB) as the suspension compresses. This allows chain tension (mainly) to counter the squat. But this also creates significant bump feedback. We want to be clear on one thing: There is no free lunch here. Have an increasing effective chain length between the cogs – get some degree of bump feedback.
The one area where some multi-links (this usually means 4-bars) may have a slight benefit over conventional mono-pivots is in bump feedback to the pedals.
4-bars offer the possibility of both variable curvature and tight, circular curvature as the rear axle moves relative to the main triangle. Both of these possibilities allow for a center of curvature inside the rear wheel radius. Tight curvature above equilibrium allows the suspension to counter squat at equilibrium, while more effectively limiting feedback. Bikes with tight circular curvature should be run with little or no sag to prevent problems from feedback under suspension extension.
However, as we have noted, 4-bars on the market today do not provide significantly varying curvature and only the Giant NRS, The Rocky Mountain ETS-X70, and Cannondale Scalpel, have significantly tighter curvature (though one might find that the ETS-X70 does not have a small enough radius, nor the Scalpel enough travel for this to be significant for him or her, with regard to pedaling).
This means that almost all non-URT designs on the market today (with the three exceptions) must make essentially the same compromises between feedback and anti-squat. Some prefer the rearward tilting axle path and the generally increased efficiency provided by the anti-squat. Others prefer the smoother pedaling over bumps provided by a more vertical path tangent at sag.