As I mentioned at the outset of this review, we will be doing the Rumblefish II review in a bit different manner than our other tests. The Rumblefish II has been ridden and written about by us a fair amount already, so our initial impressions are already here. With that behind us, I thought it would be a good idea to focus on some of the design features of the HiFi/Rumblefish line up that are unique and also a bit on the DRCV damper which is on this rig.

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The Spec: Let’s run briefly through the spec sheet for the Rumblefish II to get ourselves acquainted with what we are looking at here. The frame is a new design from the ground up which features hydro-formed aluminum tubing and eschews the carbon fiber seat stays of the previous generation HiFi line up. The frame is kitted out in a mostly Shimano drive train featuring XT cranks, shifters, and front derailluer matched up with an XTR Shadow rear derailluer. The brakes are Avid’s Elixir CR and the wheels are Bontrager Rhythm Elites shod with 29-3 tires and set up tubeless. The suspension bits are all Fox. The 120mm front fork features the FIT damper, a tapered 1.5″ to 1 1/8th inch “E2” steerer, and a 15QR through axle. The rear damper is the exclusive Fox DRCV damper and in this bike it yields 110mm of travel. The rest of the bike is set up with much of Bontrager’s excellent componentry.

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The Front End: Okay, so with the specs covered, let’s take a closer look at the front end of the bike. Here we can see the tapered head tube which houses the E2 steerer and gives the front end of this bike a solid feel. The Fox RLC 120mm FIT fork has adjustability for spring rate, (air), rebound, low speed compression, and lock out force. The fork has the G2 offset, which is 51mm, and works with the frame geometry to give the bike better cornering and slow speed handling traits without sacrificing downhill stability.
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The Fox fork also features the 15QR through axle. Now you may or may not be a fan of the standard, but a through axle is a welcomed sight on a 29″er, especially so here. A 120mm fork is a long lever arm just waiting to twist! That through axle keeps things pointed where you want to go. So, whether or not 15QR is a good idea versus 20mm axles, I will leave for another post!

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The Back End: What is going on in the rear of the Rumblefish, (and also with the new HiFi line), is a huge improvement over the past 29 inch full suspension efforts made by Fisher. Looking at the image above you will notice the rear stay doesn’t terminate at a pivot above the drop out anymore. Now the pivot is concentric with the rear axle. This is, of course, a utilization of Trek’s excellent “ABP” design, but I think it does something even more important to a 29″er FS design: It makes the length of the “lever arm” the tire contact patch has on the pivot shorter, and the ABP acts a bit like a through axle. These two things tighten up the feel of this rear suspension tremendously. Of course, the original intent of the ABP, (Active Brake Pivot), was to allow the rear brake to not lock out the suspension when the rear brake is applied. Does it work on a 29″er? Yes! It is, as Grannygear said, “the real deal”. This ABP thing really works nicely, and with the added, (and to my mind, more important), benefit of stiffening up the rear end feel, you can’t really go wrong here.

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Another “big deal” with regards to the re-designed HiFi/Rumblefish models is the moving of the swingarm pivot to a point behind the seat tube. This effectively shortens the swingarm which also helps make it stiffer. It also helped Fisher reduce the chainstay length to under 18″, to approximately 17 7/8ths”. All making for a bit stiffer, and a bit better handling bike. In terms of riding, this seems to be working, as the rear wheel stays planted a bit better than before with the old HiFi. It’s also a wee bit better at lofting the front end when necessary due to the shorter wheelbase.
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The swing link was also changed from a pivot on the seat tube to now where it is located on the top tube. The link is also shorter and lighter. The seat stays are also radically different from the previous version. Now it is a one piece unit, which greatly increases stiffness in that part of the rear end. Besides all the frame and suspension changes, I should note that the Rumblefish II comes with the 12-36T cassette for a wider gear range.

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The DRCV Shock: Here’s what makes a Rumblefish a Rumblefish, and not a HiFi. The two models share many features, frame parts, and even rear travel figures, (110mm), but the way the two bikes feel couldn’t be more different. That is mainly due to this Fox shock developed in conjunction with Trek’s Jose Gonzales and his team of engineers. The HiFi line comes with Fox RP2 or RP23 dampers with a high Boost Valve setting. (Boost Valve is a sort of internal platform which allows for a ride that feels stiffer when pedaling out of the saddle and during hard efforts) The Rumblefish; however, has the DRCV which is an entirely different animal internally. The DRCV also features a Boost Valve, but its setting is far “lower”/softer than the HiFi’s is making for a better feel over smaller trail chatter than the HiFi line has. Where the DRCV really is different though is when the shock gets about halfway into its travel.

That’s where the second air chamber comes into play. Yes, the DRCV is a dual chamber shock, but instead of having a second, external can from the main shock body, Fox and Trek designed this damper to have both chambers stacked, one on top of another. When the shock shaft is about halfway into its stroke, a rod connected to a piston is activated opening the second chamber. This effectively makes the volume of the first chamber, which is being compressed, become open to the second chamber’s volume, and thus Fox and Trek engineers were able to figure out how to keep the spring rate flat through a longer portion of the shock’s stroke.
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Okay, whoop-de-doo! How does this affect you, the trail rider? Well, it makes it seem like the damper never is doing anything but soak up the smaller hits, at least by the “seat of the pants” feel of it. Your eyes will tell you otherwise, but the bigger hits feel much like the smaller ones. The rear end feel doesn’t stiffen up until you get pretty close to bottoming out. I remember the first ride on the Rumblefish where I thought I had the damper set up wrong. The bike couldn’t be close to using up all its travel, could it? But when I dismounted and checked the O-ring on the DRCV’s shaft, it was a millimeter or two from the end!

It seems like the Rumblefish has more travel than it does, and you do not feel as though you are getting bounced around as much because of the DRCV. It keeps things calmer, and it really seems to work as advertised. The caveat? You have to spend more time in setting it up correctly to access all the potential of this design. You just can’t spend a few minutes with an air pump and go. It will probably take upwards of a half an hour to get it sorted on your first attempt. It’s well worth the time though, as their is nothing else out there quite like the DRCV feel.

Okay, that’s a wrap on the main features of this rig. Now it’s time for an update on the ride performance of the Rumblefish II, which should be ready to be posted in a couple of weeks. Stay tuned for that and more……….

Note: This bicycle was provided to Twenty Nine Inches for test/review at no charge. We are not being paid or bribed to give a positive review. We will strive to give our honest opinions throughout.