Five Reasons WTF Linkage Is Best
Originally posted Jul 25, 2020
Photo by Dave O'Dowd
At Structure we regularly hear comments such as: “If it ain’t broke, don’t fix it.”, “A solution looking for a problem.”, “Overengineered just for the sake of overengineering.”, “Too many moving parts and too many things to break.” Are they right?
Telescoping (AKA telescopic) forks have been around since 1908, and they work reasonably well under most circumstances, so it’s no surprise that people question the advantages of Structure’s WTF (Without Telescoping Fork) Linkage suspension.
Let’s take a hard look at the limitations of telescoping forks and at five ways WTF Linkage addresses them
1. Telescoping forks have a fixed axle path
There’s no getting around it; the axle of a telescoping fork always travels in a line that follows the angle of the fork legs.
How WTF Linkage differs: With linkage suspension, axle path can be finely tuned to match that of the rear, retain front center length, and limit tucking of the wheel under the rider.
Verdict: Linkage wins, with greater stability, predictability, and ability to carry speed through a corner.
2. Telescoping forks aren’t always compliant
Telescoping forks are subjected to tremendous bending loads – experienced as side loads on bushings and seals - while attempting to slide in response to impacts. Because no bushing material is frictionless, riders often experience momentary resistance to free movement of the suspension when the bushings are heavily loaded.
Additionally, telescoping forks are asked to steer, handle braking loads, function as dampers and springs, and serve as structural elements. Because of this, repeated hard hits (such as in braking bumps on a steep descent) under braking and/or while initiating a turn can result in a telescoping fork “packing up” and becoming harsh, un-compliant, and short on available travel, which can – and often does – result in a crash.
How WTF Linkage differs: Structure’s linkage suspension rotates almost frictionlessly on big sealed cartridge bearings, so there are no bushings to bind. The shock is not asked to be a structural element, so its seals and piston experience no side loads. For a rider, this means that the suspension is always smooth, always ready to respond.
WTF Linkage is better able to separate steering, braking, and suspension forces from one another within the system. For example, under hard braking the suspension remains free to move and steering inputs are freely transmitted to a rigid fork that is not serving as a spring and damper.
Because each of the linkage arms in WTF linkage is short and stiff, overall system stiffness is 25% greater than that of the best current enduro telescoping forks, resulting in a better sense of connection between rider and front contact patch.
Verdict: Linkage wins, with greater stiffness, improved control, smoother travel, and more predictable behaviour.
3. Telescoping forks dive heavily under front braking
We’ve all experienced it: Under application of the front brakes, a telescoping fork immediately dives, shortening the travel and leaving less suspension available to deal with bumps. On average, telescoping forks have a dive inclination of 30% or more. In an effort to limit dive, many riders over-pressure their forks, resulting in decreased bump compliance.
How WTF Linkage differs: Much as rear linkage suspensions are able to limit the effect of braking forces on suspension movement (most engineers make an effort to achieve neutral braking effect, causing the suspension to neither elongate nor compress), WTF front linkage uses geometry to limit the effect of braking forces on suspension kinematics. The orientation of the links is such that braking loads at the front caliper are countered by the tendency of the links to hold position until a bump force is encountered.
For the rider, this means less dive under braking, less rider weight transfer to the front of the bike, and more available suspension. The result is a sensation of staying in the cockpit, centered in the bike with a more reliable sense of the relationship between rider center of mass and the front tire’s contact patch.
The Structure SCW1 provides an eccentric at the rear pivot of the upper front control arm, which allows a rider to select a brake-dive reduction (versus telescoping fork) of 17%, 22%, 33%, or a racy and firm 41%. If you have ever experienced an OTB (“over the bars” crash), you know how brake dive can ruin a great day on the trail. WTF Linkage significantly reduces brake dive.
Verdict: Linkage wins, with less brake dive and better bump compliance than telescoping forks. With Structure’s rider-selectable dive reduction system, riders can decide how much or how little dive they want for a given location or riding style (e.g. dirt jumping versus techy descents).
4. Telescoping forks become steeper as the front dives
Not only do telescoping forks readily dive under application of the front brakes, but the steering head angle also steepens, reducing trail - a measurement of front wheel steering stability - and front center length. This means that the front wheel tends to tuck up and back with big hits or heavy front brake application and steering becomes twitchy when a rider needs stability most. Ideally, stability should be maintained or increased as the suspension is loaded, but telescoping forks tend to become less stable the harder they are pushed.
How WTF Linkage differs: Under pitch – compression of the front suspension alone, WTF Linkage retains the static 66.1° fork angle - within one degree – throughout the entire range of travel. A telescoping fork that begins at 63° static angle will steepen to approximately 73° under the same compression.
Under heave - compression of both front and rear together – WTF linkage slackens the fork angle from 66.1° by a whopping 7.7°, arriving at 58.4° at full bump and elongating the trail measurement by as much as 50%. On the trail this means that WTF Linkage becomes more stable the harder it is pushed, and it’s a difference you will notice on your first - and every - ride.
Verdict: Linkage wins, retaining or slackening head angle and becoming more stable the harder the suspension works.
5. Telescoping forks are no longer simple or maintenance-light
It may surprise you to see this point on our list, but telescoping forks are not as simple or maintenance-friendly as one might expect. With complex valving to mitigate brake dive and damp compression and rebound, specific fluid requirements, and bushings and seals that require replacement with wear, even the best telescoping forks require occasional rebuilds, and maintenance intervals for some forks are as low as 50 hours. To complicate matters further, many shops have months-long lead times for fork service, and fork rebuilds aren’t cheap, often costing $200 U.S. or more per visit.
How WTF Linkage differs: WTF Linkage may look complicated but is actually no more complicated than any typical linkage rear suspension. At Structure, we use common 6903 sealed cartridge bearings for all main pivots front and rear that can be found at any MTB shop. Because we protect those bearings with double wiper seals on all main bearing caps, wide bearing spacing, internal alloy sleeves, and some of the toughest carbon layup in the industry, we recommend 250-hour intervals for bearing inspection. Should you need bearings, Structure covers the cost of the bearings (but not installation) under our lifetime frame and bearing warranty.
The most complicated item in the system, the front shock, is identical to the rear shock and is serviced in the same way. In fact, anyone who can work on rear suspension can easily maintain a Structure bike.
Verdict: Linkage wins, with easy service, industry-standard bearings, and long service intervals. Better yet, you will never again replace fork seals, bushings, or fluid.
To those who say, “If it ain’t broke, don’t fix it”, we say, “It was broke. We fixed it.”
Come ride the SCW1 for yourself and see if you agree with Structure owner Matt K, who says: “I’ve owned 200 mountain bikes and this is my favourite bike ever, by far.”
