Chris Currie mountain bike suspension patent drawings

Editor’s Note: Chris Currie has been in the industry for years, many of which he’s spent quietly designing, patenting and slowly but surely developing his own full suspension platform. In this new series, he’ll give us a peek inside the process of creating something new, the myriad ways to bring it to market and the challenges of it all. Without further ado, here’s Chris:

Eighteen years ago, I started an online bike shop called Speedgoat out of an old one-room schoolhouse in the mountains of Southwestern PA. I didn’t have “start-up capital,” a background in web development, or a business degree. All I really had was an obsession with bikes and a wife who was just crazy enough to go along with me. For fourteen years we worked with the best companies in the bike business, building up thousands of custom bikes for riders around the world. We knew the names of our customers’ dogs, even if the customers lived thousands of miles away. It was that kind of business.

In 2010 I sold the company to people I thought could take it to the next level, but they were a trainwreck. Frustrated with the new owners, I left in 2011. In the years since, I moved west to manage sales, marketing, and customer service for Velotech in Portland, Oregon, while moonlighting for Stan’s NoTubes, where I’m now Creative Director. Through it all, one personal project that started at Speedgoat ten years ago has stayed with me. I had an idea for a bike.

Since 2004, I’ve been quietly developing an entirely new suspension platform. The original idea started innocently enough, but got out of control pretty quickly. I ended up teaching myself Solidworks to be able to draw and dimension what I was trying to visualize in my head. I applied for a patent in 2007 when the numbers started telling me this could be something special, and was granted a patent for the design in 2010. Until you have a rolling prototype, you have nothing, so I didn’t make a big deal about any of this, but somehow the design started to earn a bit of an underground following among engineers and product managers. In 2011, I was in such a low place after leaving Speedgoat that I started writing about the design on a blog I’d started. A few early drawings made their way around the interwebs, and I started to hear from people in the industry. They were getting it. They could see what I was trying to do, and there were a lot of questions about licensing and what I was going to do next, some from people I respected very much. One day I sat down, re-read my own patent online, and started opening files I hadn’t touched since the whole company sale debacle. I had no idea how to make a proof-of-concept bike, but I knew that’s what I had to do.

Today I have six of those bikes sitting in my garage (my wife is still extremely understanding). The current prototype has 160mm of rear travel (6.3″) and is built on 27.5″ wheels. It has a 66º head tube angle when used with a 160mm travel fork, but it’s designed around a straight 1.5″ head tube, so it accepts AngleSets and Works headsets with tapered forks, making the full HT angle range 64-68º. Seat tube angle is 74º. Axle path is one of the special things about the design, and it lets me keep the chainstays to 429mm (16.9″) with plenty of clearance for 2.4″ tires.

The bottom bracket height is adjustable with a chip system built into the lower shock mount, and the frame uses an 73mm English bottom bracket. I had an idea for a PF30 system that wouldn’t creak, but at some point it just didn’t make sense to deny the superiority of good ol’ English threaded bottom brackets (the worst part was admitting my friend, Jason, had been right from the start).

Dropouts are set for 142mm spacing but are modular, because there are no standards any more. Prepare to be boosted. The frame has a removable ISCG tab and can accommodate a front derailleur, if you really want to do something like that.

The current bike is really just a test bed for suspension technology, though. That’s my patent, and that’s what stands out to anyone who rides the bike. Back in 2005, I made an absurd wish list of performance criteria that included obvious things like chainstay length and axle path, but also more esoteric details about pivot point locations for manufacturing precision, leverage ratio adjustability, and shock placement (wasn’t allowed to mount in the center of the downtube, because I’m convinced that leads to really heavy, reinforced downtubes). I ended up designing the suspension to work with just about any shock orientation, though.

 

I have about 100 separate drawings of the kinematics like this in Solidworks.  It looks stick-figure, but the lines can be rotated through the bike's suspension movement and precisely measured. Then there are all the 3D parts drawings of the shapes that fit into place.

I have about 100 separate drawings of the kinematics like this in Solidworks. It looks stick-figure, but the lines can be rotated through the bike’s suspension movement and precisely measured. Then there are all the 3D parts drawings of the shapes that fit into place.

But one performance criteria set the tone for the whole system: The bike wasn’t allowed to bob at all on the climbs, even in a shock’s ‘descend’ mode. I mean no tiny pulse at the rocker, no subtle cable movement: zero. If you were under power, only bumps could make the suspension work. But -and this was the stupid “cake and eat it, too” part- you also had to be able to compress the suspension just by standing beside the bike and pressing down with one hand. I’ve ridden a lot of bikes that pedal great, but go jackhammer on you when you really need them to work. I’ve also ridden a lot of bikes that just don’t pedal well. Based on what I was seeing with instant center behavior and axle path on the computer, I thought this design had the potential to balance pedaling and suspension in a very different way. And it does.

I don’t come from an engineering background, but being stupid’s never stopped me before. I wasn’t a web developer when I created one of the first online custom bike configurators at Speedgoat, either. I’d be the first to say I have “fixation issues.” I have this natural gift for making my life completely unbearable. There’s probably a gene that keeps people from obsessing about ideas until they’ve stopped sleeping and wrecked their health. I don’t think I have that gene.

Here are the front triangle drawings built up from the original kinematics. This is the Large frame size.

Here are the front triangle drawings built up from the original kinematics. This is the Large frame size.

Back in 2005, the original business part of the idea was much simpler: develop a less expensive private-label bike as a compliment to Speedgoat’s high-end brands. The sensible thing to do would’ve been to pick up an open mold hardtail from Taiwan or China -just point to a picture in a catalog and move on to thinking about paint jobs- but I went down the rabbit hole. I’d been around to see some of the first suspension systems used on bicycles, and I’d spent so much time building and riding great bikes from Santa Cruz, Titus (and later Pivot), Niner, Intense, you name it, that I just couldn’t stop thinking about suspension systems. I’d work a fourteen-hour day at Speedgoat, then doodle pivot locations on pieces of scrap paper until the small hours of the morning. I started to see what really went into these designs, thought processes of brilliant guys like Joe Graney, Chris Cocalis, Dave Weagle, the ingenious ways Steve Domahidy and Chris Sugai were dealing with bottom-bracket drop issues on 29ers. One of the best things about trying to design something new was learning to really see what was already in front of me, the intent in other people’s designs. That’s when the insane wish list started.

In 2012, I started working with fabrication places both in the U.S. and Taiwan to create the current test mules. I worked with an engineer at Zen in Portland to make sure I had usable drawings and was accounting for all the components out there. After all, it’s nice to have cranksets that rotate and other basics. I hoped to keep fabrication in the U.S. because I thought that made more sense for prototypes, but Zen was really swamped, and no one had the time to take on the project, or even really estimate how many months it would be before they could. I ended up having to go to Taiwan, where I could get an estimated completion date.

Having a bicycle frame made in Taiwan is exactly like everyone thinks, and nothing at all like everyone thinks. The level of complication and overall expense actually went up in Taiwan -they’re not really into CNC machining one to two units- and communication becomes its own world with its own set of challenges. The problem with developing a product in Taiwan isn’t that they won’t build what you want; it’s that they will. Any detail you’ve missed, any problems with your design, get amplified and duplicated if you aren’t paying attention. I’ve invested in tooling and production for a dozen frames at this point. Any small detail that wasn’t caught and fixed with the first prototypes would now be wrong with those frames and the tooling needed to make them. Learning that process was both scary and amazing. If not for a key quality control guy over there, the whole thing would have been nearly impossible. It still seems impossible, but the first pre-production bikes are here and just about ready to meet the press and get test rides. At least one bike will be at Sea Otter.

The white frame here was  from the original prototypes and the silver frame is the current pre-production model.

The white frame here was from the original prototypes and the silver frame is the current pre-production model.

What happens now?

I don’t know. I wanted to make a great bike, something different from everything that’s been done before. I think I might have actually pulled that off, but I’m still prepared for the whole project to just come to a stop. Then I guess I’m supposed to realize I’ve wasted too much time and money chasing this, except I’d do it all over again. Given the increasing level of interest in the system, it’s also possible the design won’t have been a waste of time. I went to Interbike and rode as many new bikes as I could this year, thinking I’d realize my bike wasn’t that special and I could come home and pull the plug on all this, but nothing I rode pedaled as well, and even some of the terrible pedaling bikes didn’t handle small bumps nearly as well. I’d never ridden some of the big brands before, and I was a little shocked at how bad some of them were. There’s definitely a reason lockouts are still around. It’s probably impossible to be objective when you’ve put this much of yourself into an idea, but I tend to be pretty critical of myself -the last five years alone were spent just refining the design until I was happy with even some pretty minor details- and there does seem to be something really good going on with this design. Every time I’m about to quit, knowing there’s something potentially great here pushes me one step further.

To figure out where this goes, I’ve once again taken over the Speedgoat.com domain name and am relaunching Speedgoat as a design shop for the new suspension system, and possibly as a small bike brand. I got burned pretty bad by the people who took over my company, but I fought to get the domain name back. There’s a good bit of interest in licensing the design right now, and Speedgoat.com will be where I offer information about the system. Beyond that, my current ‘market research plan’ is to show people the bike, let as many people ride it as possible, and see if anyone wants one. That plan’s probably not going to win any marketing awards, but I have to focus on my day job, and I don’t see any reason to bullshit people. I’ve made something I think works really well, but my means are limited, so it won’t be carbon fiber or have color-changing paint or anything. I’d like to get some feedback from people, keep refining, and see what happens. That all starts at Sea Otter.

But, we’re getting ahead of ourselves. In future posts, I’ll discuss what it takes to create and patent a new design, what I’ve learned along the way, why anyone would be crazy enough to try to do this, and where the project seems to be going. If you’ve ever been curious about developing your own bike or patenting a design, I’ll be happy to answer as many questions as I can in follow up articles. I don’t claim to be an expert at this, but I’m happy to share anything I know, and help anyone interested in doing your own thing. The press will finally get a good look at the bikes this Thursday at Sea Otter, but if you’re curious to find out more about the bike, you can sign up for news at Speedgoat.com. A little under two thousand people are already on the list, and I promised to share news and photos of the bike with them first.

67 comments

  1. Jaded Industry Type on

    So it’s got a front tri, a rear tri, a shock, and lofty claims about suspension performance. How is this different from EVERYTHING I’ve seen before? Guess I’ll have to wait and see…?

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  2. gsmith on

    Ok, so how exactly does the linkage work and what’s so special about it? What’s the axle path like? None of the drawings clearly show what is going on.

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  3. Jerry on

    I remember Chris and even though I’m from Canada I did stop in and bought a Titus frame from him. Supercool shop, and I hope things work out for him. I used to love playing with his custom bike builder. Speedgoat is a great name for a bike company, good luck.

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  4. JB on

    @gsmith: My strong suspicion is that the lack of clarity is intentional; I’m guessing he’ll spill the beans at Sea Otter and via the Speedgoat site.

    @Andrew: totally agree: I really enjoyed reading this, and it brings me no small measure of joy to know that there are still people out there who are committed/focused/intent/stubborn enough to do something like this.

    I, for one, am certainly intrigued: the design may be amazing, it may not be amazing, but I’m betting it’ll be thought-provoking either way. I’m looking forward to seeing photos and an explanation of the design- and to riding a demo bike!

    Reply
  5. David on

    High-forward linkage-activated single pivot, unless the lower pivot is only attached to the rocker, in which case chain tension provides anti-bob but there’s a rearward axle path???? Definitely looking forward to seeing how this plays out!

    I bought my wife a Titus Racer-X from Speedgoat way back in the day. Speedgoat was always a great shop to deal with, despite my location north of the 49th. Good luck Chris!

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  6. gsmith on

    @out for a ride

    Nope! lol. It can’t be that great, there’s not a lot you can do to make suspension better that hasn’t already been widely done. We can already create whatever axle path is desired (using various VPP, FSR, etc etc type layouts). Feedback through the chain limits the use of extremely radical rearward axle paths while using an idler pulley (as seen on a few recent DH bikes) is going to decrease drivetrain efficiency (and add weight).

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  7. pk on

    I think I figured out whats going on. Its a pretty genius solution. If I’m right it’s a new take on vpp but with a better axle path.

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  8. Josh on

    Bought a Santa Cruz Blur first gen from Speedgoat and picked it up in person. That shop was awesome, I remember it fondly and whenever I pass through western PA I wish I could stop there. When I bought the Blur it was one of the first production runs and I had to wait 6 months for it from Santa Cruz. Chris very patiently kept me updated via e-mail on it’s status and the build was great. I still have that bike and even though it’s a “lowly” 26 incher, it’s still great fun.

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  9. Carlos on

    The idea is very interesting, the concepts are clear and a man with the right attitude, check!

    i’m going to follow the project very close.
    Best of luck in Sea Otter.

    Reply
  10. Ripnshread on

    Looks like a 4/6? bar with a lower linkage that rotates in the 1-4 oclock positions in front of the bb? The double mount looks like one for a linkage and one for a shock mount? Wish ya well Chris. Looks sweet. Can’t wait.

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  11. Muther on

    Knowing what i know about mechanical engineering, I still have yet to see anything even close to what my engineering mind would call the ultimate bicycle suspension. If true, this could be a remarkable bike. Rear-ward axle path, with chain stays that don’t telescope. Very nice.

    The same chain stay length through out the travel would seem to me to neutralize much of the effects of the chain. I wonder about braking, though. It will be interesting to see what comes of this.

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  12. Ascar Larkinyar on

    the dumb down explanation is it’s a double moto-link suspension. even dumber version, four link design.

    the bottom link travels rearward and lengthens the chainstay and chain while the upper link travels in a normal suspension capacity.

    there are going to be drawbacks to this idea. unstable at speed and in tight fast turns do to bike length getting longer/shorter. undue tension on chain and shortened chain life with possible failure along with non-engineered pressure on fragile drivetrain.

    pedal bob still needs to be controlled by shock(pedal platform or brain).

    i am sure i can come up with more speculation, but to be fair lets just wait till this comes out. i applaud anybody who comes up with a new idea.

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  13. fast foreward freddy on

    This is just another dual link ala dw-link, vpp, maestro, switch link. the real magic in this suspension design is the legal juditsu that allows another company to make bike with a dual link without stepping on the others patents. It will work great just as the other dual link designs, but in no way is it revolutionary.
    Same chain stay length as the hd3 btw.

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  14. PowersUSA on

    Kudos for pursing your dreams. I wish I had the confidence in my own design to commit the necessary time and expense to take it as far as you have.

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  15. chasejj on

    Modified DW link. The lower link placement might allow a slightly shorter chainstay.
    Kinematics probably are slightly different.

    I totally get Chris’s obsession. I use to do the same (I am an ME). But conversations with other patent holders in the industry led me to sticking with my day job. Getting and defending a patent is a very expensive endeavor that can leave you bitter and exhausted.

    The problem is there is always a rocket scientist like Weagle who is sitting back and issuing some mind blowing thing a month after you just made 5 prototypes.

    Reply
  16. Ol' Shel' on

    For those who may not know, it would be natural for a rear suspension to squat as you accelerate, because a bike/rider combo has an extremely high center of gravity. Earlier, low-pivot designs did squat each time you stomped on the pedal because of this. They weren’t inefficient, but they felt like they were robbing your power.

    To make riders FEEL better, chain-induced anti-squat was designed in. Some of your leg power is used to counter this natural squat under acceleration, by trying to extend the suspension in approximately the same amount that it’s wanting to squat. As riders, we care far more about the impression of efficiency than actual efficiency.

    People are obsessed with suspension that resists initial motion because the media has told them to want that. Most people would be much better off with a system that is active and actually absorbs small bumps.

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  17. Bill Davis on

    I wish Chris all the best. First, he’s gonna have to get people on this design, whether it be from a demo tour or other means, but I can’t imagine many people preordering and paying for a radically new frame upfront through crowd sourcing. I’m sure this frame will be in the $2500 plus range, probably higher. He’s always been obsessed with punching above his weight, so lets see how his rig compares to the titans within the industry who have millions to spend in R&D. We all might be surprised.

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  18. Padrote on

    that the suspension should not activate at all during pedaling is a bad defining criterion. for a multitude of reasons.

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  19. D-unit on

    It’s basically Switch Link stuff like found on the SB-66. Slight difference in link length, but same configuration.

    Reply
  20. Joe on

    As someone just starting to think about how to produce and market my idea in the bike industry, this post was fascinating. I’m really looking forward to the future posts because currently I have no idea what to do.

    Reply
  21. Jose on

    Suspension design today are many and can be called at this point in time a dime a dozen. Execution as was mentioned here is the issue.

    Reply
  22. Jose on

    To say there are no standards anymore is wrong. There are standards that any builder can use. There are more of them now. So what??? Just pick what are the better standards and use them. There are way fewer standards on bicycles than anything else. So I say to those who whine about standards, get some perspective.

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  23. greg on

    It appears that the main difference between this and most dual-link DW systems and their imitators is that this one’s links lead from the main frame to the rear triangle. The rear triangle connects to the links’ FRONT pivot and the front triangle is attached to the links’ REAR pivot.
    interesting. Analysis will determine if it makes a functional difference from what’s already out there.

    Reply
  24. craigsj on

    “…They weren’t inefficient, but they felt like they were robbing your power.
    To make riders FEEL better, chain-induced anti-squat was designed in. Some of your leg power is used to counter this natural squat under acceleration, by trying to extend the suspension in approximately the same amount that it’s wanting to squat. As riders, we care far more about the impression of efficiency than actual efficiency.
    People are obsessed with suspension that resists initial motion because the media has told them to want that. Most people would be much better off with a system that is active and actually absorbs small bumps.”

    All of this is completely wrong. Pedal bob IS inefficient because energy from your legs goes into activating the shock (which is designed to dissipate energy). Designing in Anti-squat, on the other hand, does NOT use leg power to counteract the bob, the motion simply doesn’t exist in the first place. Lastly, a bike that bobs when you pedal is not “more active”, in fact they are typically less active because they have more oppressive low speed damping.

    (deleted)

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  25. Mr Mojo Rising on

    Chris, according to Don Belt’s linked in page, Speedgoat is his personal webpage. You better have a talk with that old man.

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  26. LaurelHighlander on

    The above is an interesting revision of history, from a guy who was always looking to “go to the next level.” Enough time has past that we will all either forget, move on, or fail to care about the actual downfall of Speedgoat and the business that the Currie’s ran into the ground:

    2 year prior to “selling the company to people I thought could take it to the next level” the death march started as they hired a Pittsburgh “executive” with no cycling experience to lead “sales growth” as the chief operating officer. Where is Don Belt now?

    http://reviews.mtbr.com/don-belt-joins-speedgoat-bicycles-inc-as-chief-operating-officer

    Best of luck, again. I enjoy your revision of history and wish you well. Poor poor Speedgoat, back from the grave that you dug and sold. Maybe Ben Serotta would like to go in 50/50?

    Reply
  27. PowersUSA on

    I love it when all the Monday morning arm chair engineers come out when a “new” design is presented. I’ll spare you my analysis.

    Reply
  28. Frank "The Tank" on

    Well I’m certainly interested. The design appears to be sound and the movement makes sense. I’ve been looking at the pros/cons for different frame designs the last few years as it’s getting time to replace my current FS rig and this layout certainly fits my needs. I’ll certainly be watching this closer as things develop, I just hope I don’t have to buy something else in the meantime as I’d like to swing a leg over this and see how she flies. Final geometry will be a big determining factor though, as I’ve found a lot of things “work”, but few feel right, and this looks like it’s in the “feels right” bracket to me.

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  29. John Benham on

    Hmmm, actually, many armchair engineer designs might be pretty sweet if they devoted the time and energy like Chris has. Kudos to Chris for pursuing. The fact is there are a ton of great bikes on the market. To say his design bike rides better than any at Interbike is a bold and confident statement. Again, kudos to Chris.

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  30. Pedro on

    I bought several bikes from Chris – especially loved Yeti 575. He allowed riders here (Ligonier, PA) to up their games exponentially & I’m sure his designs will be highly effective.

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  31. rod on

    Go Chris! I love to see creativity and thinking outside the box. Even if it’s someone creating something (in this case it’s a bike) that isn’t ground breaking, they are creating. They are making it their own and putting their soul into it. I don’t think anyone should ever dump on someone else’s design or creation. When was the last time you created something or fabricated something? Constructive feedback or different ideas are great, but all the negative comments just aren’t necessary. If you want to go ride a big box companies bike because you feel they have the best suspension or prettiest design, then go ahead. And ride on happy. If this guy wants to create something different that may or may not be better, rock on. I applaud him for taking us along for the journey and being open and honest about the experience. I personally am selling my all mountain 27.5″ carbon wonder bike and buying a single pivot, aluminum bike from a tiny company out of Colorado. Both are really, really good bikes and I wouldn’t have believed an aluminum, single pivot could edge out my state of the art vpp, but with an open mind I test rode it and I’m sold. The forward/low geometry are extreme, but make an amazing ride. For me, I believe it is a better bike for the type of riding I like to do. And is because some one want scared to try and create something new, going against the grain. …and did I mention single pivot? Amazing.

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  32. Dave on

    Haters gonna hate, trolls gonna troll. I’ve ridden the sh*t out of one of those protos all over the pnw and it’s an incredible machine. Chris is an even better guy, best of luck.

    Reply
  33. jake on

    Good on him for giving it a go, and also for being honest about who he is and what he does. Bringing a custom frame to fruition on its own is an impressive feat, let alone a half decent one. If you’re reading this Chris – let me tell you that the so-called mechanical engineers that come out of the woodwork don’t often understand everything that’s going on either (I know this because I am one too), you really have to devote a lot of passion and private research to fully understand all kinematics and their interactions.

    There’s really no reason that a non-engineer would be more or less successful in their quest provided they do their homework. I’ve spent years learning and analysing this stuff and the only thing I know for sure is that I still have a lot to learn. In fact, the more I know, the more I realise I don’t know. 🙂 Rock on and enjoy your bike, hopefully others will too!

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  34. MyShiningOne on

    No mention of this project being dubbed project “Danzig”?? Chris rules. Love his writing, candor and humor from his blog. Best of luck Chris!

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  35. ginsu on

    Based on the video show on the DirtRag link, this design does not meet the objectives spelled out by the designer.

    You can clearly see the pedals affected by cycling the suspension.

    You can clearly see the that engaging the brakes will ‘lock up’ the suspension and keep it from cycling freely under rear braking.

    Clearly, there are already superior designs to this one which don’t have these issues.

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  36. Chris Currie on

    Just wanted to thank everyone for the encouragement and feedback. Even the extremely critical comments are helpful, though it’d be great if more of you could actually ride the bike to better understand how it really works. I was happy so many people did get to ride it at Sea Otter, and the responses there were very positive. As I’ve said many times, maybe nothing will come of the design, but the suspension definitely raised some eyebrows among those who rode it in Monterey.

    Now I need to figure out how to let more people try it out. Anybody in the Portland/Vancouver area?

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  37. mr mojo risin on

    My statement was that of fact that Mr. Belt was still claiming Speedgoat as his personal website. Personally, if I were Currie, I’d want to know and have him change this as nothing is worse than someone trying to take credit for someone elses blood, sweat and tears. Not really sure about the other things Mr. Rocky Mountain Highlander, but wish you all the best, as if it weren’t for you and Speedgoats other dedicated employees, Speedgoat would have never attained such success before Belt and Chicago flushed it down the toilet. Still find it hard to believe the company was sold to a bunch of nitwits for a mere 30k. Ill buy one of these new frames in a heartbeat when they become available.

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  38. ChrisG on

    @craigsj that is a very good explanation of anti-squat. @MyShiningOne you are right this bike is the bike that first made a public appearance at http://www.canootervalve.com/tag/project-danzig/ @chasejj I think you are wrong to associate this linkage with the DW-link. It is a four bar that strongly resembles the first generation Yeti Switch bike but this one forgoes the eccentric pivot hardware for a more conventional short link. Actually, some aspects of the relative positioning of the pivots seems closer to the NEUF design (Decathlon/B-Twin) that Sotto Group lifted from Decathlon unaknowledged and onsold/licensed to Yeti after repatenting it as their own design. Still, the raised level of anti-squat and the use of conventional linkage hardware are possibly enough to make a claim of originality for the new design. Chris Currie regrettably, apparently oblivious to the family resemblance between his new bike and the existing Decathlon design, like the Sotto Group before him, fails to cite the Decathlon patent – US6712374 B2 – in the patent documents that he filed.

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  39. ChrisG on

    Just had a look at the linkage being activated in a video on the dirtragmag page referenced above. There is no doubt that Chris Currie’s linkage is a refinement of the suspension linkage that Decathlon has been using for many years now. Currie can claim originality in some respects but the overarching similarities are unmistakeable.

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  40. Chris Currie on

    Thanks for reading guys. Probably the most obvious distinction between my design and Decathlon’s is their eccentric. That eccentric is more than just a means to an end for them: it’s a key component of the patent itself. But much more significant even than the eccentric, the real difference is the location and behavior of the instant center. They’re using a little more conventional IC that still lives primarily in front of the BB shell, and in front of their lower link. I never wanted that. When the IC starts in front of the lower link the way theirs does, you get some very different behavior that I was actually trying to avoid.

    I think the Decathlon is a brilliant design, but my starting point (even before Solidworks, back when I was cutting out paper pieces and moving them around) was really a swingarm that rotated in an extremely compact way–almost around its own center. Everything began with that, plus a belief that connecting the swingarm to the lower pivot ahead of the lower pivot’s connection to the main frame could create some desirable pedaling advantages without locking out motion entirely. Add in a probably absurd desire to see how vertical an axle path I could get away with, and that’s really where my head was at back in the early days. So a key aspect of my design and patent involves a very different pivot point from the Decathlons and similar designs. I think Decathlon did some really cool things, but I’m committed to chasing this rearward IC concept that was conceived to do something a little different, and has continued to evolve in that different direction. The rearward IC has lots of challenges, but can also do some really great things, and I don’t think it’s used enough.

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  41. ChrisG on

    Chris,
    I set out my understanding of what is going on with the ‘Danzig’ linkage here below. I would be grateful if you could confirm or correct the perspective I present. As as result of having had to organize my thoughts I have realized there are significant differences between your linkage and the Yeti and Decathlon linkages so I want to more fully acknowledge the originality of your work which I understated in the comments above. Still, I think you have granted a degree of similarity between your linkage and certain others so let me start there. The similarity I perceive between your suspension linkage design and the Decathlon and Yeti (pre-Infinity) linkages that preceded it is that they all have rearward migrating ICs. There are differences in the ‘zones’ in which the migration occurs (as well as other subtle or not so subtle differences). IC migration for the Decathlon happens in the spacial area ahead of the lower pivot as you say. Thus IC migration is fully within the zone prior to the inflection point or switch (emphasized by Yeti) where the lower link remains in a state of counter rotation relative to the upper pivot/link/rocker. IC migration for the Yeti occurs in the area around the lower pivot and there has been a deliberate design decision to effect a reversal in the relative rotation of the lower link (from counter rotation to sympathetic rotation) at around the mid point in suspension travel. So the zone of IC migration is around that inflection point. Your linkage appears to have IC migration again around the area of the lower pivot but at a somewhat more rearward position than the Yeti. In contrast to the Yeti design IC migration in your design is configured to occur at and immediately following the moment that Yeti would describe as the switch (i.e. in the rotational direction of the lower link). The Yeti design defining inflection/switch point roughly corresponds to the fully extended suspension position in your design. So, it is there, albeit less noticeable. In your design the links are moving in sympathetic rotation at all times. As relative motion of the links starts from that inflection point it is to be expected that the rate of lower link rotation would be slow at first and would pick up pace as the suspension moves deeper into travel.

    That’s about as far as my speculative powers can take me. Is this a reasonable summary of things? Is there any special relevance that attaches to the reaward IC path or the particular positioning of the IC in this spacial area or are the advantages cached out in standard terms – good anti-squat/pedaling and a good trade-off/balance of pedaling and kickback? Do you see benefits in path curvature and CC migration also with this design?

    Reply
  42. Chris Currie on

    @ChrisG That sounds like a pretty accurate analysis, though I’m not completely sure the Decathlon doesn’t hit that inflection point, too, and my design’s definitely behind that point. I didn’t have the bandwidth to do anything with my design for years, and then Sotto/Yeti’s original design was the first system that appeared with a rearward migrating IC, and I knew I had to build a proof-of-concept. That was the similarity I latched onto, despite their emphasis on the other aspects of their design. I knew how well that rearward IC movement could work, but I do believe there are other aspects of my pivot locations that are highly advantageous.

    Now I just want some people to ride the bike and let me know what they think. More frames are on the way to hopefully make that happen soon. Nothing beats actually riding the bike.

    Reply
  43. John Benham on

    I’m surprised the industry hasn’t adopted Currie’s design as the new standard for efficiency. People still want Pivots and VPP, but once people have a chance to ride one, wait, they already have. Back in the day, Currie said Stans was a hokey design compared to UST, but is now working for the company??

    Reply

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