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Blog - Blog 

Five Reasons WTF Linkage Is Best

Apr 01, 2022 Posted by: Loni Hull
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.”

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What makes Structure's Pivots So Special

Apr 01, 2022 Posted by: Loni Hull
What makes Structure's Pivots So Special

Originally posted Oct 16, 2019

photos by Mike Levy

How was Structure able to build a full-linkage suspension platform that stands up to the toughest rides and riders while offerilong a 250-hour bearing service interval?
It's all about thoughtful engineering. Come along for a closer look.

Our front linkage system looks complex at first, but is actually very similar to a rear four-bar system. In fact, it uses the same hardware and bearings as our rear main pivots.

Removal of the front control arms reveals details that make our pivots extremely durable. We start with large, strong, 17 mm collet-type axles.
Removal of the axles is simple and gives a view of the bearing caps, which provide precise spacing between suspension arms, bearings, and frame.
Each of the main bearing caps comes with an x-ring seal to keep water and dust out of the bearings, which is key to bearing longevity.
Removal of the 30 mm main pivot bearings reveals alloy through-frame inserts and wide spacing between bearing seats. These features prevent distortion of the pivot system and uneven side-loading of the bearings to increase system stiffness and bearing durability. The eccentric bearing cups (pictured above; 2 sets provided with each bike) of the upper control arm can be installed in one of four positions and reduce brake dive versus telescoping forks by 17%, 22%, 33%, or a whopping 41% to further enhance the stability of our linkage system, which offers the vertical travel equivalent of a 170 mm telescoping fork and 25% greater lateral stiffness.
We built our pivots to last and provide smooth, confidence-inspiring performance for the life of each bike. Last, but certainly not least, anyone who can service rear suspension can easily service a Structure SCW1. Why sweat the smallest details? Because we'd rather be riding than wrenching. Wouldn't you?
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Race Demos at the Sea Otter Classic

Apr 01, 2022 Posted by: Loni Hull
Race Demos at the Sea Otter Classic

Originally posted Aug 30, 2019

It’s a big deal to see a machine that began as a pencil sketch become a physical reality, especially when the benefits of defying the current paradigm are not immediately apparent to many.

The idea of coupling modern design software with advanced carbon composites manufacture to address the limitations of telescoping fork performance was not without its detractors. “Telescoping forks do a great job these days. It’s incredible what people are doing on them and how fast bikes are becoming,” some argued. Others said, “You’re going up against huge players in the industry and well-established ideas of what a bike should be. This won’t be for the faint of heart.”

Those concerns were not unfounded. But every time I looked at the potential for linkage front suspension to offer improvements that would really benefit riders, there was clearly something there: An axle path that would do just about whatever I wanted. Reduction in brake dive. Similar leverage and motion ratios front and rear. Better retention of wheelbase throughout suspension travel.

Would it work, though? Would the end-result justify the cost and commitment involved in tooling for carbon fiber, which was the only material that seemed realistic for production? Would the bike ride as well on the most challenging trails as it had ridden a thousand times in my head?

In March of 2019, the Structure management team decided to find out. We visited our partner factory in Taichung, Taiwan to examine the first sample SCW1 frames out of the molds. We needed to see with our own eyes and ride the bike to know the truth, whatever it might be. I admit I was as nervous as an expectant father. Maybe there would be a fatal flaw in the design despite painstaking attention to every detail (we hoped) by a large team of engineers. Maybe there would be a frame component that required major redesign, or the bike would weigh 40 pounds or ride like a pig. Our previous alloy and rapid prototype bikes had indicated that everything planned for the production bike should hit the mark, but you never know until you put your own ass in the saddle and on the line.

The team hard at work.
After a team of factory staff and engineers gathered to help us build a sample frame into a complete bike, Joe, our agent, arranged our first ride on Super8, a trail in the hills above Taichung. Joe was also kind enough to lend us his own carbon enduro bike for reference, a telescoping fork-equipped bike so fresh out of the molds that some of us hadn’t yet heard of the brand (it’s a big one).

From the moment we started down the trail, the SCW1 felt special. Smooth. Longitudinally stiff but with outstanding small bump compliance. Composure everywhere. Noticeably less dive under braking, but not at the expense of handling. The bike tracked precisely and just wanted to go. Were we biased? Maybe, but we had an extensive checklist of details to examine critically and a reference bike with up-to-the-minute geometry to catch us out if we were making excuses.

Our first time down the hill, I was on the SCW1 and trying to pay attention to the trail and to everything about the bike at the same time. Rick, one of our management team, was on Joe’s bike and seemed to be loving it. He also seemed to be keeping up just fine, although we weren’t pushing hard yet.

With one lap completed, we swapped bikes, and I had to admit right off the bat that the new bike from the other brand had a lot going for it. The rear was snappy, pedaled efficiently, felt dialed, and had a fresh 36 mm telescoping fork up front. Time to step up the pace. 
Loni Hull on his first ride.
Rick was in front of me on the SCW1 and was absolutely devouring the trail, drifting tight corners and carrying a ton of speed. After a few corners, I gave up trying to keep pace and settled for meeting him at the bottom.

When we got to the shuttle van, Rick was all smiles. “Damn, this bike is fast! I really didn’t expect it to be this good without something needing to be tweaked” he said. Then he lowered his voice, almost as if not to jinx his next words.

“I gotta tell you...This is a podium bike.”

I’ll never forget that moment, because I thought so clearly to myself, “Man, that would be awesome. Maybe someday…many months from now.”

Fast forward one week. After a whirlwind flight back to Calgary, Alberta followed by a long drive to Monterey, California, we were at the Sea Otter Classic. Before the trip to Taiwan, we hadn’t even been sure we would have bikes at the Classic, but with a bit of luck and expert help from the staff at Bow Cycle in Calgary, we had managed to get two complete bikes together in time for the festival, where we planned to show off bikes, do some riding, and meet with the press to the extent possible.

What we could never have planned was to have two separate racers come on separate occasions to our booth, briefly ride the SCW1 on asphalt, and sincerely ask if they could swap their familiar, well-prepared bikes to race the SCW1 in Cat 1 and Cat 2 DH and dual slalom events.

With a hard swallow, we said yes.
Dave Smith
That was how David Smith and Ryan Sullivan, two racers who did not know each other or us, and who each had about an hour of practice time on two separate SCW1s, came to win three podiums out of three races entered: bronze in Cat 1 DH; silver in Cat 2 DH; and gold in the Cat 2 dual slalom.
Ryan Sullivan
It was like something out of a dream, and certainly blew past our wildest expectations. For a young brand to hit the ground with a new linkage suspension system featured on a model in its first week of existence and come away with three medals was as close to a fairy tale as anyone can expect in a mud and blood sport like MTB, but it really happened.

Podium bike indeed.
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