Banshee Rune on Pinkbike
From Drawings to Reality: Introducing the 2013 Banshee Spitfire V2 — More Mountain Bike Photos
A Banshee bike really has to be ridden to fully understand what all the different design considerations we make and how they translate into a thrilling riding experience. Few bikes in their respective categories pedal as well or feel as stiff. The bikes will give you the efficiency and control to ride beyond your current limits. So what’s exactly involved in creating a great bike?
Banshee’s design approach When designing a frame we look first at the intended use. The tubing materials and thicknesses are chosen for the correct weight and strength for its intended use.
Then, we design custom tubes to optimize the strength and stiffness and to minimize the weight.
Next, the ideal geometry is selected. This includes: fork length, head angle, top tube length, seat angle, bb height, and chain stay length. Of course there are many conflicting ideas in regard to what the “perfect” geometry for a certain type of bike is but with over 25 years riding, racing and designing high performance bikes we have developed some certain formulae for frame geometries.
Instead of saying that we want a certain head angle, we look at the steering trail because this more accurately describes how a bike will react to steering input. We then choose a head angle that achieves this trail with the length of fork we wish to use.
Top tube length and seat tube angle work together to influence rider comfort, confidence and the rider’s ability to generate power. Therefore different riding disciplines will require different top tube lengths and seat tube angles.
Instead of using BB height, we try to make the “drop” of the frame match the fork travel and ground clearance requirements.
Chain stay length affects the natural turning radius of the bike and works in conjunction with the trail. Chain stay length is kind of like choosing skis - shorter slalom type skis and shorter chain stays are best for quick turns and nimble handling conversely longer giant slalom type skis and longer chain stays are better for higher speeds and longer carving turns.
Once we have these geometric criteria determined, we draw the bike in its ideal form with its intended fork; this is the base design. Some adjustments of the base design are undertaken to adjust the geometry to work in the various configurations..
Suspension designs. Currently with the new breed of bikes there is a lot of marketing spin on what creates the ultimate bike and which type of suspension design it would have. Many riders get confused and are constantly wondering which one is the best. Well to be perfectly honest there really is no clear winner and a well thought out simple design will outperform the latest multilink monstrosity. Our thoughts on the matter are to select the suspension design that will have the best possible traits given they type of riding the bike will be used for. We have come to some truths we feel work for us and realize that one suspension design doesn’t work for all purposes. There are priorities to consider and the reason there are so many other designs is because of the differing opinions on which trait is most important.
For Banshee a bike that needs to have efficient pedaling performance as one of its top priorities excels using a short link 4-bar system. There are many different types VPP, DW-Link, Maestro, they are similar in that they have a short lower link between the chain stay and the mainframe. This does not mean by any stretch that they share the same properties or traits because even a pivot that is different by a millimeter can translate into quite different ride characteristics. Our short link 4-bar is the VF4B.
Just as we have found the short link 4-bar an exceptional platform for a performance pedaling bike, we have also found the Turner 4-bar system allows us to create an extremely solid backend that is free from energy robbing lateral flex, sure footed, and stable when landing large jumps. By using the Turner 4-bar linkage the optimal axel path can be achieved whilst also having the ability to position the shock in a desirable location low down in the frame and protected from the sprayed up mud and water. Not only this, but the nature of the design allows the designer greater flexibility to dial in the ideal progressive linkage, which cannot easily be achieved on a single pivot bike.
All Banshee bikes use full compliment deep groove bearings for greater stiffness and longer bearing life. Unlike the FSR, Horst link, or ICT designs, which have a pivot in front of the rear axle, the Turner 4-bar has the rear wheel axle pivot around the massive swing arm bearing which is attached directly to the mainframe increase greatly the lateral stiffness. This combined with the internally ribbed chain stay and seat stays, and the triangulated pivot locations ensure a solid footing railing berms, landing massive airs, and putting the power to the back wheel without the lateral energy robbing flex.
KS - Link Suspension This new spin on the virtual pivot was designed by Keith Scott [hence the name KS-Link... the name was inspired by Dave Weagle]. The main features is the extremely short links a minimal rotation as the shock is driven directly by the rear triangle. All pivots have been mapped and the forces calculated to create a well engineered wheelrate when combined with that accompanying shock rate. The goal was to create a pivot system that was able to take sideloads really well and minimize the amount of rotation and wear on the pivots and the shock DU bushings. In addition to its solid looks it is a suspension system that lends itself to keeping the chainstay length short on long travel 29r bikes without giving up the advantages of having a virtual pivot design.
Banshee VF4B Suspension Our VIRTUAL FLOATING FOUR BAR (VF4B) suspension system, seen on the Spitfire, Rampant and Rune, is comprised of a rigid rear triangle attached to the front triangle with a pair of differential linkages. Our combination of a rigidly constructed rear triangle, cold forged links and pivot technology allow the suspension to move freely, with a single degree of freedom. This solid linkage system eliminates power losses and performance robbing flex. The floating virtual pivot is located on and slightly above the chain line (depending on the travel position and which gear you are in) which reduces the effect of pedaling forces on the suspension. The axle path moves upward and rearward on a wide and reducing curve for the first part of travel. This eliminates squat in the “pedaling zone”. The rearward initial axle path also causes the wheel to travel in the direction of the bump forces, making the suspension feel incredibly smooth while pedaling at high speed over square edged bumps. In the middle portion of the suspensions travel, the axle changes direction on a tightly controlled curve, from up and back to up and forward. Once the axle begins moving forward, the axle path curvature increases to control chain growth and pedal feedback.
The upper links bring the bump forces to the shock and create a progressive to regressive suspension rate. This crossover rate, when coupled with an air shock, provides a smoothly progressive suspension feel.
Banshee Turner-4Bar The Banshee Scythe use a Turner 4-Bar linkage with geometries and pivot locations accurately calculated and designed. Each rear suspension linkage achieves optimal suspension characteristics for the bikes intended use, without compromising on exceptional stiffness or desired ergonomics. The results of all this painstaking design work… bikes with handling and control that outperform expectations.
To understand fully just why the bikes feel so great to ride, the suspension characteristics have to be examined individually…
Leverage ratios Each linkage exhibits a smooth progressive travel. So as the suspension compresses the leverage ratio continuously reduces to a final ratio of significantly less than 3:1. This essentially means that as the rear wheel moves through its travel, it becomes gradually harder to compress. There are three positive attributes of progressive designs:
Axle Path The path the axle follows determines many aspects of the suspension performance. All Banshee full suspension bikes have a slightly rearward axel path at the start of the travel designed to smoothly absorb square edge bumps with minimal impact on the riders speed and control. As the suspension moves further into the travel, the axel path gradually becomes more vertical. This is designed into the system to limit the amount of chain-stretch experienced as the suspension approaches the bottom out position.
Chain-stretch Chain-stretch is defined by how much the distance between the bottom bracket and the rear wheel axel grows as the suspension compresses. It is in fact desirable to have a small amount of chain stretch apparent around the sag point of a bike, as the tensional forces experienced by the chain under pedaling reduce pedal bob. However if the chain-stretch of a suspension linkage is too large, then an undesirable characteristic called pedal kickback becomes apparent which effects the regularity of the pedal stroke, and puts unnecessarily large forces through the chain. Banshee bikes achieve the optimum chain-stretch characteristics by careful design of the rear suspension pivot locations and geometries. This ensures a design superior to competitors in terms of pedaling efficiency by eliminating pedal bob, and minimizing pedal kickback.
This is definitely not the last word in suspension design, and a full 4 years of engineering school, and a physics major will still not give you all the answers. As amazing as it is to think about it, bikes are continually being reinvented and a quick look to designs only 5 years ago shows the developments that are still being made. I can't tell you what the future will bring but as we continually push beyond what we've done in the past, the riders will benefit from the hard work, and ingenuity that we are working on daily to move the designs forward.