Jamis 2017 Full Suspension Bicycle Technology http://www.rbinc-sports.com
THE MAGIC OF MP4
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.
Our mp4 designs rely 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 two really good ones. And because everything happens at this one location, we can place it in such a way that it minimizes braking influences, reduces pedal kickback and unwanted movement due to chain tension.
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 bell-crank 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.
On the XCT and Defcon, our pivot placement produces a slight, rising-rate spring curve. 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 mid-travel rigs like the XCT and Defcon.
On the shorter travel XCR, we’re pure linear, so the suspension provides a constant pedaling platform from the beginning for efficient power transfer off the line, on climbs and sprints, or when hammering in the big ring on a fire road downhill. When coupled with the naturally progressive spring curve and tune-ability of an air shock, the system is ready to soak up unexpected hits when you miss that line in a nasty rock garden.
THE LOW LEVERAGE ADVANTAGE
We’re big believers in the benefits of low shock leverage ratios. With leverage measured as the ratio of wheel travel to shock stroke. The mp4 design comes in at 2.55:1 on our XCT’s and 2.63:1 on our XCR’s and AMT’s. This is really important, when it comes to suspension smoothness and durability.
For one thing, you get better performance from the shock with a low 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 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 tune-able).
What’s more, a lower spring rate lets you run less air pressure, which improves shock sensitivity and vastly extends seal life.