Bike Check: Auckland Cycle Works' "Kind of Like a Rearward Pivot URT" Experimental Prototypes

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The bike world runs on out-of-the-box ideas. How else would we have reached the point we're at today, with dropper posts, mixed wheel sizes, high pivot designs, and all the other wackiness we now take for granted and that makes our lives easier? Even mountain bikes themselves were born from cruisers that some renegades decided to retrofit with balloon tires (the details depending on which branch of mountain bike origin folklore we believe).

Our entire sport owes itself to nonconformity, and for that reason, it's always exciting to see a truly left-field idea come to fruition. A little while back, we found the webpage for a fascinating project that we've been watching, created by British bike shop owner Gary Ewing, who fits all the criteria for a top-notch tinkerer: he's creative, intensely curious, and seems to have an endless supply of what if questions. In 2021, when he had more free time than usual amidst the pandemic, he decided to draw on a conversation he had nearly two decades prior for inspiration to create a bike.


In about 2002, Ewing was on a ride with endurance cycling legend Mike Hall and asked Hall about a bike he'd designed and built for an A-level school project. All Hall said, Ewing recounted, was that the bike design was "kind of like a rearward-pivot URT."

URT - unified rear triangle - bikes emerged in the '90s to try to balance pedaling firmness and suspension performance. By moving the bottom bracket from the frame's front triangle back onto the swingarm and putting the main pivot up away from the bottom bracket, engineer and cyclist John Castellano managed to create a system that was firm while pedaling out of the saddle but provided active suspension while seated, which was the gold standard at the time. For a variety of reasons - including the already-scary-by-modern-standards bike geometry becoming increasingly sketchy under braking forces and while descending - URT was retired about as quickly as it rose to prominence, and the bike world largely moved on. (Find a deep dive into the URT story here.) Still, Ewing says he believes in exploring concepts and wasn't convinced that the URT theory had been fully played out.

When we discovered his project, one sentence in Ewing's description stood out: "The discredited URT (unified rear triangle) design looked like an unfixably bad idea, but I wondered: if combined with other things that also appear to be bad ideas, what's the worst that could happen?"

If that's not an intriguing approach, I'm not sure what is. Enter Ewing's aluminum prototypes.

As a starting place, he wondered if perhaps a URT bike with a rearward virtual pivot motion and dramatically rearward axle path could help control some of the negative characteristics that had undone the URT design in the '90s. He built his first two URT test configurations not because he thought they would work (he was clear that they probably wouldn't), but because that seemed like a good place to start the experiment.

We at Pinkbike hear from many, many people who believe their idea is the next great thing that's going to change mountain biking forever. Spoiler: those ideas often don't live up to the hype. In contrast, it was quite refreshing - charming, even - that Ewing approached his project with pure curiosity and without grandiose claims.

"I started this whole project thinking that I’d make something that was vaguely like Mike’s idea, as a fitting tribute to him, that I’d learn a whole heap of new skills, and I’d get a bonkers thing to hang on the wall of my shop and an interesting YouTube vid," he wrote.


For the first experimentation and design, Ewing built his initial models using Lego Technic, not the CAD programs used by most builders, because he likes the ability to make quick changes and engage with his designs hands-on, even if the process has a bit less finesse than computer-based systems. Plus, as someone who grew up toying with Lego Technic models of all kinds, he's plenty familiar with that style of tinkering. For initial proof of concept, his way worked great, he said.

He did have to learn some CAD modeling and made quick progress with the Fusion 360 CAD program to get the linkages CNC’d, he said, but realized he could spend two years full-time on that side of the project and still be only a mediocre CAD designer. "It soon became clear that CAD is a whole universe of learning and knowledge, and that I’d be better off finding someone good that can do this for me," he explained.

When the Lego models took shape in the real world, to Ewing's surprise, the first prototype performed pretty well... sometimes. Pedaling hard in a high gear "required motion sickness tablets," he said, but the bike was a surprisingly quiet pedaler in low gears and the braking performance was better than expected, compared to the head-angle-steepening and wheelbase-shortening effects under braking - resulting from extension of the rear shock - that marked the historic URT bikes. Still, it needed some big changes, so he hacksawed it and re-assembled it into the second prototype, which was a bit better, he said: "The very rearward axle-path made it blisteringly and effortlessly fast on smooth singletrack. The awful kinematics of the URT design meant the suspension didn’t cope well with lumpier terrain, yet the braking performance was surprisingly good."



It wasn't the bike he wanted to ride, so Ewing had all but committed to putting the project to bed when he had what he describes as a true eureka moment - he figured maybe some of the characteristics he liked about the bike could be retained if he just moved the bottom bracket to a more standard position. Based on how the suspension linkage moves, he figured he could put a high pivot idler on the lower linkage that could be easily moved forward, backward, up, or down - within seconds, he said - to fine-tune the bike's pedaling and suspension performance.


Starting again from the ground up, he built a bike that he's calling the Marra, which features 190 mm of suspension front and rear and already has a patent pending on the suspension design. Through some more experimentation with his idler concept, he discovered that - surprisingly - the idler position that allowed for the easiest pedaling was also the position that best optimized the shock performance, he said. As for the actual measurements, the current model has a 480mm reach, a 645mm stack, and a 63-degree head angle.


He's not surprised that the bike performs well on the descents, thanks in part to an axle path that's dramatically rearward for the first half of the shock stroke but nearly vertical for the rest of the stroke. The chainstays lengthening only through the top of the stroke means that the bike should retain a fair amount of playfulness, he explained, though he's still not quite satisfied and wants the chainstays to be a bit shorter. Even so, a recent trip to Les Gets reaffirmed his suspicions that he's onto something, he said, with the bike pedaling efficiently and descending comfortably.


The next parts of the story: Ewing says he'll keep refining the Marra and plans to play with some shorter-travel top links. He's also been working on a 120 mm carbon bike that he was hoping to race at the Glentress Seven race - a seven-hour trial by fire - but unfortunately he's been sidelined by injury for the time being, and that was an ambitious deadline for getting the bike finished anyway, he said.


Hopping the other direction in travel, he's also sketched a downhill version that's almost identical to the current Marra but uses an extra linkage that alters the kinematics, making the shock stroke more linear at the beginning and more progressive at the very end for coil shock compatibility.

Looking even farther ahead, Ewing also hopes to one day make an e-bike. At the moment, though, he has plenty to keep him busy, with his suspension design patent decision approaching in August, plans to race the Marra at the Tweedlove Bike Festival in September, and a stand booked at the Bespoked Handmade Bicycle Show in October.

And we know that whatever he does next, he'll be following his curiosity, testing his intuition, and giving the bike world something new to talk about. Which is exactly what I want to see.

Follow along at aucklandcycle.works, Instagram, and YouTube.