iv) Ellsworth adds:

Motion ratio is improved by selecting a rocker arm length close to that of the lower swingarm. To provide desirable Brake Torque Isolation performance, the rear of the link must permit brake loads to be imposed at near 90 degrees (nearly perpendicular) as described elsewhere herein;...

In summation, Ellsworth claims that a 90 deg. angle between the rear and horizontal links, as is nearly the case on the Dare downhill bike, will “isolate” the suspension from brake force.

Ellsworth explains the physical motivations for the 90 deg. linkage configuration in the following two quotes:

All, or almost all, caliper brakes mount and function identically in the bicycle industry--they all must squeeze the rim in the same place, which creates a torque at that point which is then transferred into the frame at the connection points of the member on which they are mounted (for example, the shockstay 9) to the lower and/or upper swingarms (members 6, 7, and 8 in the preferred embodiment illustrated herein). As discussed elsewhere herein, if that force is aligned at a 90 degree angle, then there is no torque, and that force has no impact on the compression or extension of the suspension, etc. Any deviation from 90 degrees creates a torque moment that will pull or push the swingarms up or down--resulting in compression or extension of the suspension.

Ellsworth adds:

To prevent unwanted suspension movement, bind or preload under the forces of braking, the rear brake device (consisting of either a disc brake caliper or conventional bicycle rim brake) mounting point is attached to the rear wheel attachment upright. The angle of the rear wheel attachment upright to the upper rocker arms statically approaches 90 degrees in angle in a loaded condition, causing the torque moment induced by brake forces to be transferred into the forward frame assembly laterally with minimal horizontal torque component. This transfer of the brake forces thus will not have an extending effect or compressing effect on the shock absorber, leaving the suspension free to move horizontally when activated by wheel bump forces while the rear brakes are in operation. Positioning the rear suspension's instant center relatively close to the ground plane also helps the rear suspension's bump compliance under braking.

The second quote is very confusing, we believe due to some mistakes in word usage.  Patent wording is usually very thoroughly scrutinized, however, we believe that the reference to “horizontal” suspension motion was intended to reference vertical motion.  In addition, the reference to “torque component” is probably non-technical, since any torque, about any suspension pivots, will always have a vector at 90 deg. to the plane of the bike.  This last may be simply a matter of a non-technical writer.

If we accept the corrections to word usage in the second quote, Ellsworth seems to have an essentially correct understanding of the forces on the linkage directly from the brake.  However, as both quotes make clear, they draw the wrong conclusions in believing these forces will not affect the suspension.

Ellsworth's error is in the belief that force directed exclusively down the axis of the upper link, would isolate the suspension from braking.

Recall Figure 3.14) of the “Braking.” section.  Imagine adjusting the links to create 90 deg. angles between the rear and horizontal links, as per ICT.  It is true that the force F, from the brake, will be transferred directly down the axis of the upper link, however, this will obviously not prevent a reaction of the suspension.  It is, after all, the rider/main triangle that is suspended.  Force from the brake, directed along the upper link axis, will go into the main triangle, ultimately acting as an extending force on the suspension.  This, in turn, will contribute to the rider/main triangle pitching forward, exacerbating the jack already caused by rider inertia.

As is covered in the text associated with Figure 3.14), it is not the angles between the rear and horizontal links that matters, but the IC location – too bad Ellsworth did not stick with IC location when it was the correct thing to do.

Imagine varying the angle between the rear and upper links, while holding the axes of the upper and lower links constant, producing a constant IC location under variation.  The components of the force on the upper and lower links, from the rear link, are changing, but so too are the torque lever arms.  In the end, this variation in angle will not change the brake's effect on the suspension.  So the Ellsworth Dare would have the same braking character with a more conventional, much shorter, upper link.

Finally, in the ICT patents, Ellsworth makes a number of claims for the performance of “prior art” designs that we find very odd and worthy of note.

For example, referring to “High Single Pivot” bikes such as those, “Used by Foes, Mountain cycle, Bolder, Pro Flex, Cannondale, Marin, and others.”, Ellsworth states:

“These designs are usually very brake-torque reactive, which causes the suspension to extend and lock out.”

As noted in the “Braking” and “‘Brake Induced Shock Lockout' (BISL)” sections, we have done extensive braking experimentation on the most common mono-pivots and found them to be very non-reactive – in fact, generally the least of all reactive – to braking forces.  Numerous other riders doing similar experiments have echoed these results.

Referring to “Unified Rear Triangle” designs, “Used by Trek, Gary Fisher, Klein, Schwinn, Ibis, and others.”, Ellsworth states:

“Depending on the pivot location, brake torque usually causes these designs to compress and pre-load or extend and lock up.”

URT bikes are essentially the same as non-URT mono-pivot bikes, under braking.  As noted above, we have extensively tested many mono-pivot bikes, including the infamous, but really not so bad, Trek Y-bike.  The Y-bike was absolutely neutral under braking.

Ellsworth states of “Multilink, Low Main Pivot” designs, “Used by GT, Turner, Intense, KHS (the foregoing are all four-bar linkage designs) Ventana, Mongoose, and Diamond Back (the last three utilize a swing or bell crank linkage).”:

“The wheel travels in a near vertical path, instead of an arc, thus increasing shock absorbing efficiency and reducing energy wasting wheel fore and aft oscillations.”

This again seems to imply Ellsworth viewing the IC as a pivot.  In any case, the rear axle path curvature of a 4-bar can be as described, but most have tighter curvature then most mono-pivots, as is demonstrated in chapter VI, “Wheel Path Analyses of Some Existing Models.”

Ellsworth goes on to say:

“...currently most bikes using this design have been developed by trial and error with no clear understanding of all of the aspects of suspension function.”

Given the information above, we find this statement highly amusing.