Even though the Primer 220 is a brand-new model, it is the result of many years of thought and experience. The brainchild of Doug Bradbury, brought to life by engineer Mark Landsaat, the Primer is the next evolution of the original downhill bike Johnny raced in 1999 and 2000 seasons.
Like the original Tomac DH bike, the Primer is a single pivot bike with a linkage driven shock. But there are a bevy of improvements to the overall suspension design, linkage set up and swingarm. Let’s start with the leverage ratio and suspension rate. When we originally designed the bike, we felt an optimized design would allow us to use a standard 350 pound spring on a medium size bike and a leverage ratio that was under 3 to 1. With this set up and with a stock range of springs, it would be simple for any weight rider to set the bike up for any type of track, be it smooth, rough or anywhere in between. We wanted a fairly standard wheel path that would provide a consistent feel throughout the travel.
We settled on a leverage ratio of 2.9 to 1, with a suspension rate that is progressive up to 140mm travel and then becomes virtually linear. We did this because as you go into the travel, the rear shock itself becomes more progressive. If the bike’s ending suspension rate is progressive, and the shock is progressive, deeper in the travel the suspension will both become overly firm and the bike will not achieve full travel. The current set up allows the bike to feel consistent and smooth through the travel.
The suspension linkage is all CNC machined out of billet aluminum with oversize pivots bolts and full compliment bearings. You will notice that the linkage, like the rest of the bike, is low slung, a key in maintaining a low center of gravity. Motorcycle riders have long known that keeping the CG as low as possible is what gives the bike a light feel and allows a bike to corner well without sacrificing stability.
Speaking of stability, one of the main focuses of the Primer was nailing the geometry. We wanted it to be relaxed enough so that the bike would feel stable on fast straights, but not so slack that you would not be able to corner aggressively. We designed the bike around a 66 degree head angle and a 62 degree seat angle, with a bottom bracket height of 14.84 inches (unsagged). The geometry, combined with the low CG of the bike overall, makes the bike very easy to ride. I will quote World Cup rider Claudio Caluori directly, who did a bulk of the testing on the Primer. “Robin (Hagen) and I were really stoked on the primers,” says Caluori. “We were testing the two bikes on a really rough, rooty and rocky trail in Germany. The bike felt really stable on rough stuff. You could take it wherever you wanted.”
But all of the stability in the world wouldn’t amount to much if it didn’t have equal stiffness and strength, which is why we put an equal amount of thought (and FEA) into the shaping of the tubes. As an example, you can see a high degree of top tube and down tube shaping. You will also notice the top tube has a flat section near the head tube. The head tube impact test showed that this added strength and weld area, which in turn allowed us to eliminate gusseting between the head tube and down tube. Besides the fact that the elimination of the gusseting improves the looks a bit (please note the comparable lack of welding in this area), it was also a bit of a technical accomplishment and lessened overall frame weight. In addition, the top and down tube shapes really enhance the front end stiffness of the bike.
The Primer is designed to be used with a 200mm suspension fork. This might seem odd to have 200mm in the front and 220mm in back, but the goal is to provide an overall balanced ride once sag has been set. We recommend 35 to 45% of sag in the rear, where DH forks typically require only 20 to 25% of sag. When you are done setting front and rear suspension sag, you would have the same positive travel, and thus achieve a balanced ride.
Another goal of the new Primer was to standardize all the component interfaces. Gone is the oversize bottom bracket shell and custom wheel spacing in favor of the common 83mm/150mm combination respectively. In addition, there has been a major refocus on enhancing rear end stiffness. There’s a single-sided hex axle (provided) and the swingarm has been fully triangulated.
The finished Primer is the result of over 2 years of work and 7 different prototypes. It will be ridden by the Tomac Factory Downhill Team on the World Cup.
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