Regular BikerGene readers will know I’m a huge fan of funny front-end suspension ideas that look beyond the traditional telescopic fork in search of progressive setups that deal more effectively with the separate issues of bumps, braking, steering and cornering forces - and this one looks fantastic.
Tier Motorsports have come up with a design concept - here pictured as part of a potential R1 prototype - that uses a single-sided front swingarm and four-bar steering system to create a perfectly vertical steering axis, as opposed to the tilted steering axes found on telescopic forks due to their necessary rake.
Among the advantages of the Tier Motorsports system are the typical non-telescopic fork benefits shared by many funny front-ends - you can decide on how much you want the bike to dive under brakes, geometry and steering angle doesn’t change under brakes, steering and suspension forces are separated, etc. (see the full list of benefits in the press release at the end) - but one particular benefit of this front swingarm design is that it eliminates the need for a large, heavy, reinforced front headstock in the frame.
This leaves open the option for much lighter and more compact frame designs - even replacing the majority of the frame by using the engine as the primary stressed member. And while this concept mockup tacks on to a traditionally shaped R1, we’d love to see what designers would come up with when forks are removed from the picture.
Typically, the main disadvantages with front-swingarm systems (such as the one already in production on the hub-centre steered Bimota TESI 3D) are high costs, a ride feeling that takes some getting used to, a fairly limited steering lock and a general perception from the surprisingly conservative biker market that they don’t look like ‘real bikes.’ The Tier Motorsports system will likely run into all these problems on its way to market; here’s hoping it gets a chance to prove itself in the flesh.
More pics follow, then the press release:
The patent pending Four-Bar Steering MechanismTM is the only vertical steering axis design available for motorcycles. The advantage of having a vertical steering axis include:
1. More controllable motorcycle on rougher roads. Road imperfections tending to steer the wheel will not be fed back into the handlebars like it does on standard forks equipped motorcycles. This is illustrated here in contrast with a theoretical worst case 90 degrees steering axis (courtesy of Tony Foale):
2. Goodbye handlebar wobble (movement, sometime violent, of the handlebar occurring at higher speeds). This is a result of the actual parts moving during steering being much lighter than on conventional forks. Eliminating steering dampers also mean a quicker steering available to the rider.
3. Custom steering trail. The trail is set by 2 spacers that can be replaced in minutes. Trail being the key value controlling handling characteristics now let the user choose the right value to match the road condition and their riding style (lower = more aggressive; higher = more stable).
4. Reduced steering forces. Does not raise the height of the center of gravity while steering.
5. Reduced steering angle needed at the wheel to achieve the same turning radius as a standard fork. This is a great advantage over other front swing arm steering design as it allows for narrower swing arm which gives more ground clearance in fully leaned turns.
Expert point of view
Tony Foale, world wide recognized expert on motorcycle dynamics and author of “Motorcycle Handling and Chassis Design, the art and science”, had this to say about the front suspension and steering presented here: “The Tier front motorcycle steering and suspension system is a refreshing novel and innovative approach to tackle many known problems inherent in conventional motorcycles.”
The picture below shows an exploded view of the patent pending Four-Bar Steering MechanismTM located inside the wheel hub:
The following sketch is an horizontal cross section cutting the front wheel right above the Four-Bar Steering MechanismTM and looking down at it. It shows how the “virtual steering axis” is found by extending a line going through the follower links. Where the lines meet is the point “C” to which the wheel will steer about. This allows the use of a much smaller wheel hub to achieve the benefits of a vertical steering axis.
Benefits of the front swing arm Here is a list of advantages that front steering suspensions have over classical forks:
a. 50% anti-dive vs. 90% pro-dive with forks. The classic front fork suspension makes the front of the motorcycle dive under braking which in extreme cases can cause the motorcycle to flip forward. Having a front swing arm allows to design the front suspension with any type of positive dive (like with forks) or negative dive as well as progressive dive. With negative dive the bike will actually raise during braking. Of course most riders like to have some dive to have a feel for how hard they are braking so the ideal bike will have just enough dive to be felt by the rider.
b. Greater comfort. Because the front suspension undergoes less dive during braking it does not tend to compress the suspension as much. This allows for softer springs to be installed.
c. Lighter frame and a lower center of gravity improving handling. There is no longer a need for a sturdy frame around the upper steering column to counter force from the telescopic fork. On some models the engine can be used as the structural main frame of the motorcycle.
d. Suspension rate and dampening can easily be adjusted on the fly as on rear suspensions.
e. Constant stability. Minimal change in wheel base throughout suspension travel.
f. More precise handling. Minimal change in trail throughout suspension travel.
g. Single sided swing arm allows quick wheel removal and installation as only the wheel nut needs to be removed.
h. More compact and aerodynamic overall motorcycle design. Resulting from a lower amount of dive under braking the suspension travel is reduced (although the suspension can be designed to have wide travel for off road use).
i. Increase in braking performance. During braking the reduced dive result in less weight transferred to the front which allows for the rear wheel to absorb more braking power.
j. Greater power to steer the front wheel. Steering ratios can be easily adjusted to provide greater power to steer the front wheel on heavier bike or less handlebar travel to make tighter fairings possible on sport bike. Geared up ratios on sport bikes does not require excessive force at the handle since the four-bar design is easier to steer.
k. More pronounced separation between suspension and steering/control. Allowing adjustment of both to achieve optimum performance. The percentage of antidive can be varied with minimal effect to the steering (On telescopic forks, the dive under braking causes the wheelbase to get shorter, the rake to steepen and the trail to reduce.)You can leave a response, or trackback from your own site.