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The Critical Geometry Frame

Miscellaneous 8 171

This innovative suspension system developed by Product M is so named because the design maintains the relationship between the critical human interface points on a bicycle (the bars, seat and pedals). By suspending the rider and keeping the distance between the saddle and the bottom bracket fixed, this design is meant to eliminate, as the website explains, the “unnatural crunch like activities that happen on a bike where the distance changes.” You can learn more about the design at the bicycle section of Product M’s website.

I first saw a prototype of this design, called “Suspend This” at the time, at an event that was held in Product M’s Atlanta office in the late 90s. Back then, I remember thinking that the concept was a good one and I hoped to see it on the market someday. In the following years, I forgot all about this idea, but recently I learned that Schwinn licensed the idea for one of their comfort bikes, the 2006 Sierra DSX. I was also happy to read that the licensing agreement with Schwinn is non-exclusive, so there is still a possibility that this suspension idea could be used on a performance oriented mountain bike as well. I think it is a pretty marketable idea in a very competitive industry. What do you think?

At any rate, Congrats to Mark, the principal at Product M and primary developer of the bike, for getting this patented suspension design on the market. Very cool.


  1. robodobo August 4, 2006 at 12:38 pm -  Reply

    Does the M stand for Moronic? It looks to take the almost nonexistant benefits of the suspension seatpost and add weight and complexity. The dumbest part of the whole design is that the travel comes at the cost of bottom bracket clearance. As the bike uses it’s travel, the bottom bracket shell moves toward the ground. I can just imagine trying to clear a log or something and then having the lower bottom bracket height cause me to hang up on the log and doing a faceplant. There has to be a better way to keep constant saddle height.

  2. Graham August 4, 2006 at 1:38 pm -  Reply

    It seems interesting, but is this a problem that the customer is complaining about. Sure, the first time you ride a suspension bike it seems weird and awkward getting used to the different geometry positions you find yourself in…but after a while you adjust to make this an advantage.

  3. James August 6, 2006 at 8:03 pm -  Reply

    Robo, You may have some questions about the validity of the design, but you shouldn’t use the relative anonymity of the web to say things that you would not say in person. I do encourage discussion in the comments section, but I ask that you use common courtesy when offering a differing opinion. I think that you lose credibility with comments like this one.

    Graham, You are probably right. I doubt that this is a problem that current full suspension bike buyers are complaining about, but it could be a possible way to open the market for suspension bikes to wider audience. I personally ride a short travel rear suspension mountain bike that was definitely designed with cross country racing in mind. That type of suspension is effective and helps to maintain speed over rough terrain, but it doesn’t necessarily increase rider comfort very much. That is OK with me because a speed advantage is what I want from the bike. My point is that different customers want different benefits from suspension, so I like to see new ideas thrown into the mix. Schwinn obviously see the critical geometry suspension idea as a comfort oriented rider benefit. Some riders who will venture off road with a bike occasionally (not the target market for the Sierra DSX) will also value comfort over performance gains, or will at least value both equally. A completely new type of suspension design like this will not be everything to everyone (I don’t think Robo would buy a bike like this for instance), but it could give some consumers a viable new option to consider. I think that is a good thing.

  4. Mark McJunkin August 7, 2006 at 11:03 am -  Reply

    Thank you for your enthusiasm for this concept James. As for Robo – Go to your local bike store with a ruler and cycle the rear suspension of any rear suspension design through its top and bottom position – you might be amazed to see that on effective suspension designs the BB shell moves up and down. Also see the video footage of the CGF in action.
    it works quite the opposite of what you are describing.
    Graham – I have worked in the bike industry for many years – I have built this design out of passion for the true riding experience of a light agile cross country mountain bike. It is actually more efficient than a hard tail in climbing and is a blast down a hill. Even if I am the only consumer that appreciates this ride – the investment has been worth it.

    If you guys are ever in Ga – give me a call and we can set up a time for a test ride.


  5. robodobo August 7, 2006 at 1:04 pm -  Reply

    My apologies. I realize that all designs affect the bb height, but this design seems to do so much more than others. I am certainly open to new ideas and I’d love to try it and wish you the best of luck with the design.

  6. mark mcjunkin August 7, 2006 at 1:54 pm -  Reply

    The BB only travels the same distance that you would find on any trailing link suspension – about an inch and a quarter. Under power the CGF suspension actually pulls the BB up and away from obstacles – Look at the Rock Climb video.


  7. Anonymous August 8, 2006 at 10:56 am -  Reply

    oooo.. a new bicycle suspension! I don’t know how it works, but it’s pretty ugly.

  8. :)ensen August 11, 2006 at 3:12 am -  Reply

    I didn’t do any research into your development dates, but I know that the recumbent guys in Vancouver were arguing something like this in the early 90’s. If you pre-date this, then good on you for getting it patented.

    The result of those discussions was a consensus that several problems had to be solved, probably with the damping system. First, the vertical movement of the thru-tube is not likely to be at right angles to the chain, especially over the range of triple chain-ring. This can will lead to suspension decompression under pedalling forces. Second, there will be huge twisting moment (torque) under pedalling forces that will have to be controlled by either the shape of the tubes or some kind or horizontal torsion bar system. Third, some riders will have a problem with changing body position relative to the handlebar system. Fourth, during activation, there will be a moment centred on the contact patch of the front wheel and this will be at some non-ideal angle to the direction of the linear travel. And last, we couldn’t figure out a way to make the whole thing lightweight. I’d be curious to know how you’ve solved these problems.

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