Paging Derby yet again
Is the linkage on the Pace bike going to ride similarly to the DW link?
This bike is destined to be for sale in the UK fairly soon all things being equal
Thanks in advance
The dw-Link IC location isn’t so high at any common point of travel. There may be some noticeable pedal kickback on the Pace bike, unlike the dw-Link bikes. Only riding it would reveal the facts about the pedal feelback.
The braking geometry looks pretty good for stability and traction modulation for good handling. It would have a more rearward path producing less braking traction than a dw-Link, so it may be no better than a monopivot for braking overall.
With such a high IC mapping, this looks like downhill oriented suspension, with exaggerated bio-pace, an extending reaction to pedaling, tuned for acceleration with little pedaling momentum resistance, rather than a mild to moderate bio-pace for best rough trail climbing suspension such as dw-link. Higher IC’s within the wheelbase tend to produce high “virtual pivots”, where the line from the axle to IC intersects during travel.
This Pace bike may or may not infringe on the Anti-squat effects in pending international patents. I image DW’s legal patrol will investigate it.
Bottom-line is I’m guessing this won’t be as good climbing, having a little more pedal feedback resistance to bump momentum than DW’s designs (too much anti-squat), but will have a smooth pedaling feel, much like a VPP design but without as much pedal feedback as VPP. And rear braking won’t be nearly as high in ground traction. The suspension looks to be mainly downhill oriented.
Instant Center. The IC is a mapped point in space where lines drawn through the pivots of multiple swing links intersect.
Originally Posted by Gregg K
The IC is very loosely termed a "virtual pivot". Although it is really never a center of rotation, rather it is a focus point of two or more directions of tension.
With 4-bar suspension the IC is a reference point for drawing a virtual swing arm line through the axle and IC at any moment of travel.
By tracking the intersection of the virtual swingarm lines during incremental change in travel position you can map an effective virtual swingarm pivot where the axle path rotates around, and for pedaling tensions and bump compliance has equal leverage and torque with the frame as a physical pivot in the same position.
What is interesting is the IC does act nearly exactly like a physical pivot at the same place on the frame during rear braking tension, or with solid axle-housing such as shaft-drives secured to the frame. While braking the wheel becomes an extension of the rear link due to the brake friction. And with a drive-shaft the drive line is in line with the slope of the axle path, while with chain drive the drive line is not aligned with the path.
Where the swingarm (or virtual swingarm line of a multi-link) line intersects the drive line (driveshaft line or chain line), there is an intersection point, which is another IC, a Driven-Net-IC (the effective virtual pivot during acceleration).
And another line projected from the rear wheel through the Driven-Net-IC describes the squat angle.
Rear suspension squat reactivity during acceleration can be compared and measured as a percentage by looking at the point where the squat angle line crosses the front wheel base plane. When the point of the squat line crosses the front wheelbase below the height of the Center of Mass the frame rotates rearward around the Net-Drive-IC.
DW has patented a specific rate of change in squat percentage for his dw-Link suspension.
Unlike chain drive, braking (normally) has no brake line tension from hand lever to caliper. While braking, the rear axle link’s IC is the Braking-Net-IC. So only the tension direction at the IC affects the frame about the wheelbase. During braking the direction of tension at the IC and virtual swingarm (or monopivot swingarm) is always concentric and in the rotation direction of the rear wheel due to the friction connection of the brake. When the IC is tensioned downward with the rear wheel between the wheelbase the frame is rotated rearward around the front wheel netting a squat effect. And visa-versa, with the IC is rotating with the rear wheel outside of the wheel base the frame is tensioned to rotate forward around the front wheel in extension with the rear suspension.
There is increasingly significant extending braking reactivity when the IC is located beyond the wheelbase, even without considering other extending reactions from weight shift (inertia) and front braking. Only when the rider weight is very far back over the rear wheel would extending brake reactivity be somewhat useful, to extend the rear wheel downward into trail depressions.
Some downhill racers like this outside the wheelbase IC alignment of add-on “floater links” such as by Brake Therapy. There are few examples of this extending rear brake reaction for trail bikes, the early Busby design of the GT LTS (then considered a downhill bike) and all current Ellsworth ICT bikes have this most unstable handling design.
There is the most stable rear braking reactivity when the IC is just below the CM. But there is a tradeoff in bump compliance and stability, where relaxing the compressing (squat) reaction to rear braking by locating the IC more forward but still within the wheelbase, enhances other extending reactions to braking allowing the suspension to rise into a softer spring rate travel range. And the remaining squat reactivity is able to maintain traction without lifting the rear wheel away from the ground with stronger rear brake modulation.
The current DW-Link and some shorter upper link Horst link designs have this most ideal balance of rear braking high traction and handling stability.
(Perhaps I can put some drawing together and edit them into this post later.)
I had a feeling what IC meant, but didn't want to guess.
And on top of it, you gave a wonderful lecture on the DW Link. Now I'm beginning to understand it a little. There's a lot of thinking that went into it. Far more than I originally thought. I mean, it's just a four bar mechanism when one looks at it. But it's what one doesn't see that is so complex.
I'm familiar with radius of curvature. And an instant center would be where the center of that instantaneous radius of curvature is. For a chain, or axle, or anything. But I think I'll just let those who are engulfed in the engineering and design to the details. I'll be very happy to ride the result.
I appreciate your time in explaining it. And it would be fantastic to see a pictorial. If you have the time and interest.