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Joe's Corner : Floaters5th JAN 2010

I was reminded recently by Gerald out at the Bike Doctor in Saskatoon that I had mentioned that I would talk about "floating shocks" in one of these articles, and I never got back to it. I hate disappointing the Canadians, especially when they need something to read on those long dark cold winter nights.

To float or not to float? That is the question.

First the definition: A "floating shock" is a frame configuration where the shock isn't attached to a part that doesn't move. In practical terms, this means the shock is not attached to the front triangle directly. In most permutations of this, one end of the shock is attached to the swing-arm, and the other end of it is attached to a link.

When the rear wheel moves vertically (what I call VWT or "vertical wheel travel"), the shock compresses. That's where the whole shock rate thing comes in check out the Shock Rate article. Shock rate is just the amount of shock movement divided by the amount of wheel movement, but done incrementally, not averaged.

It doesn't really matter if the two ends of the shock move "toward" one another, or if one end moves "away" from the other end. The result is simply the shock rate, nothing has changed. But in "bike land", its not always enough to just have a desirable shock rate, there must be something else you can claim! Like this quoted directly from an unnamed company website that sells a bike with a floating shock:

"The design re-orients shock forces in two directions for better force dispersion and, because it actuates from two directions, it breaks seal stiction faster for premium suspension performance"

Let's take a closer look at these two claims:
"Re-orienting shock forces in two directions". We hadn't realized here that the shock force was only in one direction before. That's probably because Newton's third law of motion (which we still subscribe to) states: "Whenever a first body exerts a force F on a second body, the second body exerts a force -F on the first body. F and -F are equal in magnitude and opposite in direction". Yes, that would be one plus one, equaling TWO directions. Same as, uh, you.

"because it actuates from two directions, it breaks seal stiction faster". No, actually, it doesn't. It's the same force on the seal and in the shock as any bike that has the same leverage at that point.

This is pretty elementary stuff. Especially for a company with annual revenues counted with a B, as in "How many billions of dollars did we make in 2009?" For their sake I hope this was just a marketing intern who made up some stuff and this wasn't relayed by anyone in their engineering department.

To be fair, it's possible that they are trying to say that by making the shock attach in a different way the frame structure could be changed, as the force vectors would be oriented differently. If that were the case then you'd expect the frame to end up lighter than a non-floating frame design. But that is not the case. You end up instead with a fairly complicated looking linkage sitting in the middle of the front triangle that provides, according to the bike makers themselves "no advantage whatsoever", or NAW.

Shock rate changes are nothing to scoff at. It's all about how the bike behaves to bumps, and how your shock and frame work together. But the forces are all the same magnitudes; you just switch the direction of them around a bit. Maybe that helps a frame designer out, maybe it doesn't. If it does, you should really end up with a lighter frame at the end of the day. Or at least get a water bottle to fit inside the frame. If you're not getting a secondary advantage such as that, it's not necessary to have a floating shock just for shock rate changes. So if all you have is a new spot to mount the shock, then, uh, is the frame lighter? No? Well, maybe it just gets you some space for a water bottle which is no small feat these days. But maybe, just maybe, its just some crazy links that rotate too much, wear out bushings quick and makes an inconvenient spot for a shock. Doesn't seem like quite enough to warrant an acronym to me...

Why am I saying this? Because Gerald from Saskatoon asked, that's why. In-between our marathon acronym development sessions, (ADS) we blow off steam by studying suspension design. I couldn't mention some of this stuff earlier due to a pending application, but Gerald's reminder email came in a timely fashion. On September 1st of 2009, a full forty four months from the filing date, SCB was granted US Patent # 7581743, with the catchy title "Bicycle Rear Suspension System with Controlled Variable Shock Rate". To save you the pain of finding it on the uspto.gov website, it basically covers bikes with floating shocks that achieve the shock rate that we get with VPP. ( again, read the shock rate article). The development of the floating shock and shock rate behavior was a part of the R&D we performed when working on the refinement of VPP suspension that some call "VPP2". Because when we're curious about something and we don't completely trust our computers, we like to build things and evaluate how they ride. In this case, we ended up with a mule we referred to as APP1 in early 2005:

Note that one end of the shock is attached to the swing-arm, the other end is attached to the triangular link. This particular mule was, essentially, a Heckler with a Blur LT shock rate. It rode like that too, which was a pretty damn good combination of traits. So we applied for a patent in late 2005. And then took what we'd learned about shock rates and started the process that led to the redesign of all our VPP bikes. And until September 1st 2009, and then Gerald's email, we didn't say nothin' to nobody about it.

And we didn't say much because this was neat, but it wasn't really ready for prime-time. The floating shock arrangement allowed us to get that shock rate, but it also came with some non-trivial issues. The most obvious is the bulky linkage that has to go around the shock. It's nasty. The second is the chance you might chop your fingers off if you try to adjust the rebound damping when you're riding. And a less obvious one is that the shock and pivot hardware takes a beating when the link and shock are arranged like this. The link rotates a lot, and due to the directions of the forces on the link/shock interface a lot of force is put into the DU bushings and pivot hardware, which would make it harder to design a bike that didn't have durability problems in these areas. But that's why we built the thing in the first place, because you can't learn all this from a computer model.

So, in summary, what did we learn?:
A floating shock has equal forces as a non-floating arrangement, but it "might" allow a designer to move the shock to a more convenient location. Floaters allow for shock rate manipulation, but are not the only means of getting a change in shock rate. In other words, just because it's floating doesn't make it good. Depending on the arrangement, floating shocks can be bulky and hard on pivot hardware.
Billions in revenue doesn't make you immune to Newton's laws of motion.

Got any examples of other floating shock bikes? Got something else you want an article on? Send your pics and ideas to info@santacruzbicycles.com

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