c3 He encontrado un articulo que me ha gustado bastante, un analisis sobre diferentes sistemas de suspension con dibujos de como funcionan estos sistemas. Ademas de los analisis que copio y pego, podemos poner nustras sensaciones del modo mas subjetivo posible, sin meternos en temas de que bonitas o es la mejor del mundo, simplemente las sensaciones al montar, las reacciones en diferentes situaciones etc. Con esto seguro que podeis decidir que sistema os gusta mas Está en Ingles :joystick Typical Horst Link Designs. “Horst link” designs refer to frames with lower rear pivots mounted on the chain stays, forward and below the height of the rear axle. We have not bothered to plot the Ellsworth bikes, since these will be even more circular then the designs pictured. There has been a persistent myth circulating that chainstay pivot suspensions “isolate” forces on the rear link and thus are not affected by pedaling or braking. But as has been noted in the “‘Internal Force’ Theories.” section, this is entirely false. Typical Horst link designs such as the ones below are all very circular and will perform identically to the analogous mono-pivots under pedaling. Under braking, the pictured suspensions will have a tendency to extend. The virtual pivots on some, such as the Tracer, are a bit farther back then is the case in any standard mono-pivots, but the virtual pivots are not within the rear wheel radius. Intense tracer La titus switchblade Sistema Tuner Specialized FSR The Rocky Mountain ETS-X70 Figure 4.7) shows the paths for the rear axle, IC, and center of curvature, as well as the lines perpendicular to the rear axle path for the Rocky Mountain ETS-X70. There is a fairly well defined virtual pivot located well above and behind the bottom bracket. The height is similar to that of the NRS, but farther forward. This will give the bike characteristics similar to that of a very high pivot mono-pivot; though the virtual pivot is located a bit farther back then could be the case on a standard mono-pivot. One should find quite a bit of both anti-squat and kickback with this frame, though the tradeoff will be a tad less then in conventional mono-pivots. Shock absorption should be good, in spite of the relatively tight wheel path curvature, due to the high virtual pivot and rearward sloping wheel path through travel. Having the links located above the chain line is a nice feature, however, this does raise concerns regarding lateral stiffness. Preliminary observations for frame flex, taken by pressing laterally on a pedal located at six o'clock, seem to indicate that the bike has lateral stiffness on par with typical XC dualies. The author has done some accelerations on this bike and found that the frame has adequate stiffness with regard to pedaling. Perhaps a greater concern, however, is high-speed cornering, above say 25 to 30 mph. To date, we have no observations on how the frame reacts under these conditions. This is a very unique frame design, which will probably prove well suited for some, but not for others. As always, we say that test rides should always be taken. The Giant NRS Figures 4.5) depicts the virtual pivot, while Figure 4.6) shows the centers of curvature and lines perpendicular to the wheel path for the Giant NRS. Note that the “virtual pivot” on the NRS is well within the rear wheel radius and relatively high above the bottom bracket. This design will behave very much like a “split-pivot mono”, described above. The idea behind this suspension, as explained on the Giant web site, is to have the suspension run just at no sag, with the rider's weight exactly countering the force from the shock. The wheel path is tilted well back relative to the frame, so that the chain force will want to extend the suspension. In this way, the NRS eliminates suspension activation through pedaling. The effect of a pedal stroke on the suspension is like a momentary increase in force from the shock. Force from a bump must overcome this additional force before the shock will activate during pedaling. The small radius of the wheel path reduces what will probably be considerable bump feedback. These bikes should accelerate very well, but will probably not handle pedaling through technical obstacles as well as lower-pivot designs. Tight curvature generally reduces suspension performance over large bumps to some degree, however, in the NRS, this is largely mitigated due to the high and rearward virtual pivot. In addition, the configuration of links will probably induce some locking effect of the suspension, under braking (see the “Braking.” section for a full analysis). We have no idea of precisely how Giant arrived at their geometry, or if the ideas behind any quantitative force theory they are using are completely sound. But as far as the information that they do provide goes, there is no overt error. Figure 4.5 Figure 4.6 The Cannondale Scalpel. The Scalpel is another tight-radius design. The bike was inspired by a “split-pivot mono” prototype, which can be viewed on the Cannondale web site. Figure 4.8 ) shows a picture of the rear suspension, taken from Cannondale's web site (with permission). The thin, flexible section of the chain stays is meant to act like a pivot. The path tangent starts out at nearly vertical and curves forward. The chain stay length is initially increasing, since the BB is centered below the height of the rear axle. We have not bothered to plot the path, since the center of curvature is going to be at the thin part of the stays. The intended benefits, as explained on the Cannondale web site, are an increasing effective chain stay at sag, with a tight curvature to reduce bump feedback. There is not much more to say here, since the concepts are fairly straightforward. The one thing to add is that chain stay bending does not have to be localized, as it is in the Scalpel, to produce a rear axle path radius of curvature smaller then the wheel radius. However, there is a potential advantage in localizing the bend in that the exact curvature can be more precisely controlled. The location of the bend in the Scalpel probably produces a radius of curvature similar to typical “soft-tail” designs. The initial path tangent is tilted just slightly more rearward, relative to typical soft-tails, since the bend is centered at the thin part of the stays near the top of what are otherwise rather thick stays. The extremely short travel of most soft-tail designs makes the above path considerations essentially irrelevant. However, in the Scalpel, there may be just enough travel for the tight wheel path to make a difference in bump feedback. The limited travel means that the Scalpel will essentially have no big hit performance, so tight curvature is preempted as a drawback. As always, each rider should test ride, to determine for himself or herself, whether or not any of the design considerations are significant. The Virtual Pivot Point. Starting on September 10, 1996, a series of patents was granted for bicycle suspensions with “S-shaped” paths similar to the region around equilibrium for the path in Figure 3.11 C) [U.S. patent 5,553,881,U.S. patent 5,628,524, U.S. patent 5,867,906, and U.S. patent 6,206,397]. The original design, essentially a 4-bar with reinforcing upper links, was produced under the name “Outland”. The bikes are no longer in production due to serious errors in application – the frame members and pivots were severely under-built. A second Outland design, covered in the last patent, will shortly be introduced by Santa Cruz and Intense. This design also has the potential to produce an “S-shaped” path. We will now give an explanation of the VPP concept, with an explanation of the original mechanism and some important commentary. We will then do an analysis of the current design configurations being developed by Santa Cruz and Intense. The following explanation for the VPP concept comes from the abstract of the latest patent: “A rear suspension system for a bicycle. The system directs the rear wheel along a predetermined, S-shaped path as the suspension is compressed. The path is configured to provide a chainstay lengthening effect only at those points where this is needed to counterbalance the pedal inputs of the rider; at those points in the wheel travel path where there is a chainstay lengthening effect, the chain tension which results from the pedal inputs exerts a downward force on the rear wheel, preventing unwanted compression of the suspension. The system employs a dual eccentric crank mechanism mounted adjacent the bottom bracket shell to provide the desired control characteristics.” The intent of this system is similar to that of the path we explored in Figure 3.11 C), which is to provide anti-squat during pedaling through a rearward tilting path near sag, while reducing the effects of bump feedback by turning the curve back toward a more constant radius about the bottom bracket, away from sag. Figure 4.9) shows the original VPP mechanism, at sag, with path pictured. Note that the axle is near the bottom of the region where the path takes a backward turn. Being currently unique in its ability to produce significantly variable curvature, the VPP concept is probably the most intriguing design out at the present time. The VPP concept will really prove a significant departure from prior designs if manifestations can strike the right balance in having a curve above equilibrium tight enough to reduce bump feedback significantly, but not so tight that suspension performance is compromised through the travel range. This must also be done while maintaining reasonable weight, strength, and durability. The first of these drawings, Figure 4.15), depicts the wheel axle path and the IC path (one inch intervals in wheel travel marked) as the suspension moves through its travel. The IC starts out near the BB, initially arcs up and forward, and finishes by continuing forward but slightly down. The wheel path does have a slight “S” shape, which is a bit difficult to see in this picture. Figure 4.16) depicts the wheel axle path and the path of the center of curvature, as the suspension moves through its travel. The center of curvature starts out behind the bike and quickly moves to negative infinity as the wheel path straightens. As the curvature inverts, the center of curvature jumps to positive infinity, before moving back to a final position well above and slightly behind the BB. From the behavior of the center of curvature, we see that the path is S-shaped, but only slightly. When the wheel is above one inch into travel, the normal sag for a bike with this amount of travel, the radius of curvature is always very large, until the very end, when the center of curvature moves to a horizontal position common in many of today's mono-pivots. It is for each person to determine whether or not this curvature offers any significant advantage over more conventional designs. In our estimation, the wide curvature should offer good coasting bump performance, however, we see no significant advantages for pedaling in this sort of curve. Figure 4.17) shows the IC path, the center of curvature path, and the lines perpendicular to the path, at one-inch intervals of wheel travel. Note that the perpendicular lines pass through both the IC and center of curvature positions. Figure 4.17) The slopes of the perpendicular lines again show that the wheel path has a slight S-curve. But more importantly, they show us that this bike will perform under pedaling much like a very high-pivot, mono-pivot bike when the suspension is above one inch of travel, again, the typical sag point. This means that the Blur should have pedaling characteristics similar to those well-known in the Santa Cruz Heckler, but even more so, since the path is wider and slopes back even more. That is, there will be more anti-squat then in a Heckler and correspondingly, more bump feedback. Recently, this author was able to take a short ride on an Intense VPP cross-country prototype, which has a geometry very similar to that of the Santa Cruz Blur. That ride confirmed the theoretical findings above. The suspension extended under pedaling in all small and most middle ring gears, just as would be the case in a very high-pivot mono-pivot. Again, it is for each person to determine whether or not this combination of characteristics is right for them. However, it is clear that this bike is subject to the same compromises as designs that have come before. Those wanting a very high-pivot, hyper-Heckler type of ride will like this bike. We also believe strongly that those who are truly sensitive to bump feedback will not like the bike. The Santa Cruz V10 (Linkage data): Figure 4.18 ) shows the important information for the Santa Cruz V10. The outline of the frame shows the position at full extension. The rear axle path is shown in green, the center of curvature path is shown in turquoise, and the IC path is shown in red, while the lines perpendicular to the path are light orange. Positions in travel are circled at one-inch intervals. The range of travel goes from –2.75 inches to +10 inches of travel, with 0 inches being at full extension. We have plotted the paths beyond full extension in order to show the suspension position needed to produce the S-shaped rear axle curve. Within the range of travel, the rear axle path does not achieve an S-shape. Rather, it has a wide radius of curvature until the very end of travel, with the path tangents starting out similarly to those of a relatively low-pivot mono-pivot and ending with tangents more similar to higher-pivot designs. The relatively wide radius of curvature should give the bike good big hit shock absorption, with very little bump kickback. Suspension activation under pedaling should be similar to more conventional medium-height pivot designs on the market. While we again find that there is no advantage in the tradeoff between anti-squat and kickback, and the rear axle path does not achieve the S-shape, within the range of travel, we nevertheless believe that this design should perform well in its intended downhill application, due to good big bump performance. The durability and reliability of this frame are unknown, as it is very new at the time of this writing.
