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And that’s the key word there. Viable. Because despite the variety in suspension designs, terrain and riding style, the primary goal of suspension science is pretty simple—absorb impact, negate pedal bob and neutralize brake-jack or rotor-dive while keeping tires in contact with terrain. Today’s shocks are so incredibly smart, they’re able to do the lion’s share of determining where the motion’s coming from—whether it’s the legs and pedals, or the terrain. So between today’s shock technology, and these simple suspension goals, there are plenty of available designs that can accomplish the task.
What separates the winners from the pack isn’t design, but execution. And that suits us just fine—because when it comes to detailed execution, we’re unbeatable. (Need proof? Drop by and see the roomful of editor’s choice awards we’ve earned for our bikes—no technical trickery there, that’s the power of meticulously perfect detail and execution.)
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All great engineering is based on simplicity. Find the most elemental solution possible, refine it, reduce the complexity, and you’re done. And that’s how our mp4 suspension has evolved.
Some of the other guys would have you believe complexity is a good thing, outfitting their designs with so many pivots and bellcranks it’s a wonder the wheel can move at all. We’re not convinced.
A simple design requires fewer parts, which takes less material and structure, which means less weight. And it also means fewer bearings, eliminating weight while reducing unwanted movement (every bearing has a little slop—the more bearings you have, the more slop you get).
Our mp4, mp3 and mp2 designs rely basically on a single primary pivot, located just above and behind the bottom bracket centerline. Because this single pivot takes most of the load we don’t need a plethora of heavy bearings—just this and two other really, really good ones (where the seatstays connect to the bell crank and where the bell crank connects to the frame). And because everything happens at this one primary pivot, we can place it in such a way that it minimizes braking influences, reduces pedal kickback and unwanted movement due to chain tension. Nice!
The seatstay pivot improves geometry with a consistently near-vertical axle path throughout the wheel’s travel, for better suspension movement over tiny stutters and big hits alike. And structurally, the bellcrank helps shore up the rear triangle against lateral movement and improves torsional rigidity so the rear wheel stays in plane—there’s no wandering or fishtailing because the axle’s so well controlled.
Even though our main pivot is located in the same BB location on all our mp designs, we can tune leverage rates with bell crank lengths, bell crank pivot location and shock position. Our mp2 and mp4 XC designs offer a very slight rising rate in the first 40% of travel, and then it’s linear for the balance of travel. This means you don’t get a sudden ramp-up as the suspension compresses—there’s nearly linear response in the fat part of the travel curve, for supple action over stutters and medium hits, with a bit of ramp-up as you approach the travel limits and a nearly bottomless suspension feel that’s ideal for short-travel XC designs like Dakar XCR 29ers, the XCR Race and the XC Comp & Sport. On our longer travel XCTs, 650Bs and AMT, our mp4 Trail design offers a much more progressive leverage rate. This means the rear shock can be tuned more linearly (like a coil spring) and pumped to lower pressures for a smoother, more plush ride without bottoming.
For one thing, you get better performance from the shock with a lower leverage ratio. There’s less force being taken up by the shock, which reduces stress on the shock internals. And because you’re employing more of the shock’s throw for the fat part of the travel curve, the suspension action is much smoother and better controlled.
A low leverage ratio also means you don’t need super high spring rates, which translates to improved shock sensitivity. External rebound and compression damping adjustments can be made in much finer increments, which wouldn’t make an appreciable difference on more leveraged designs. You can make better use of the shock’s tune-ability (and today’s shocks are impressively tuneable).
What’s more, a lower spring rate lets you employ a physically lighter coil spring, or in the case of air springs you can use less pressure, which improves shock sensitivity and vastly extends seal life. |
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All of our dual suspension designs (with the exception of the BAM) feature asymmetric chainstays, with an elevated straight stay on the non-drive side and a dropped, curving stay on the drive side. A straight stay uses a shorter, lighter length of material, and because it’s better aligned with suspension forces we can pare even more weight from it without giving up rigidity. The drive side is dropped and curved to clear the front derailleur and chain, and it’s shored up a bit since it also has to resist drivetrain forces. It’s not the esthetically balanced look we’re used to, but the net result is less weight, more rigidity, lots of tire clearance and smoother suspension action.
Lightness is good, but strength is paramount. That’s why we spec 10 mm shock hardware, oversize pivot bearings and high-grade fasteners throughout the suspension. You get greater lateral stiffness and torsional rigidity, which pays off in better handling and power delivery that more than makes up any time lost by carrying a few additional grams.
We carry that weight as low as possible, which is why we like our low shock mounting position that lowers the center of gravity for better handling. And we believe in the structural bracing power of the triangle. Having two of them in our suspension designs makes for a stronger, stiffer frame, qualities we maximize by keeping those triangles as small and tight as physical geometry allows for any given frame size (and also offers the lowest possible standover for the rider).
We’re also adding a little bit of extra weight in the form of the 135x13 mm Maxle thru-axle, which we use on our, XCR 29, XCT and Sixfifty B designs because it just brings so much to the table. There’s a huge payoff here—threading the rear axle into the dropouts really ties the whole rear triangle together, boosting torsional and lateral stiffness—so you get more efficient power delivery, and handling improves markedly since the rear tire’s forced to track directly behind the frame. Suspension pivots last longer, with less binding—and you experience better control under braking, with less fishtailing. It’s a win!
A better rear suspension means you’ll go faster. And that places more demands on the fork. More speed translates into higher cornering forces and braking forces, which is why we’ve include beefed up the front end on almost every Jamis mountain bike, with a tapered 1-1/8” – 1.5” head tube (the BAM offers a full 1.5” head tube).
The fork transfers most of its force into the frame via the lower headset bearing, and a 1.5” lower headset is markedly stronger than the old 1-1/8” standard. A full 1.5” head tube would accomplish the same task, but that oversize top bearing is overkill—it just bulks up the front end and adds unnecessary weight, which is why we’re glad most fork makers are embracing the tapered steerer design, so we can employ this frame spec without limiting our fork options.
A stiffer front end reduces brake chatter and gives you better steering precision. Plus a more rigid control center lets you muscle your way out of ruts, blast through rock gardens, and hold your line while bombing g-outs and railing through berms. |
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We believe in the power of design and details, and Jamis does both right. From pivot placement, to just the right size tubing and materials, to the component package, to frame alignment, it’s the manufacturing and parts specification details, not just the suspension design, that makes or breaks the ride. And we believe nobody is better at this game than we are.
If you’re shopping for a bike, you owe it to yourself to check them ALL out. Keep your eye on the big picture—does it fit your physique, your trails and riding style? In the end, what matters most is how the bike performs, in real woods, on real trails, for you. Just be sure you try a Jamis—we think you’ll like the way it works in the real world. |
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