The unique Mono Shock RA rear suspension found in a number of 2005 and 2006 Yamaha 4-stroke models requires specific set-up to perform at its fullest potential. The first and most important adjustment is to set the ride height of the suspension, using spring preload.
Rather than measure actual sled sag, Yamaha suggests measuring spring free length (with the rear of the sled off the ground) and then measuring the spring length with the rider on the sled (on the ground). The proper â€œsagâ€ and ride height is attained when the spring length is 40-45mm shorter with the rider in place. Adjustments to the cam position provide fine tuning adjustments. Moving the cam circlip provides coarse adjustment, and installing an optional spring provides even more range if required. On the Ohlins-equipped Apex GT, dual threaded locking collars are used to vary spring preload.
With this knowledge, many riders have found they are not able to attain this setting using only the 1-7 cam positions (all but Apex GT). In this case, you must remove the shock absorber from the suspension, remove the spring from the shock and relocate a positioning circlip that relocates the cam on the shock body. This shifts the entire 1-7 range of adjustability of the cam. There are three positions for the circlip, which provides enough adjustability for riders up to 300 pounds.
With the circlip in the standard position, the 1-7 positions of the cam should be able to accommodate riders ranging from 160-210 pounds (Apex ER/RTX) and from 160-220 pounds (Attak). With the circlip in the second position, the 1-7 positions of the cam should accommodate riders ranging from 200-250 pounds (Apex ER/RTX) and 220-270 pounds (Attak). With the circlip in the highest position, the 1-7 positions of the cam should accommodate riders ranging from 250-300 pounds (Apex ER/RTX) and from 270-330 pounds (Attak). Riders weighing more than this will require an optional stiffer spring (Yamaha part #8FU-47489-10-00 for Apex ER/RTX and Attak models).
When we get to the Ohlins-equipped Apex GT, the standard spring can only accommodate riders ranging from 160 to 250 pounds, using the threaded adjusters to vary the installed length of the spring. Riders weighing more than this will have to install an optional higher rate spring, and then the adjustability ranges from 170-300 pounds. The standard setting is an installed spring length of 276mm, or 14mm of preload. The spring can be safely taken to an installed length of 262 mm, or 28mm of preload. Past that, the stiffer optional spring must be installed.
Yamaha dealers can provide you with a matrix chart that graphically shows all of the weight ranges and settings so you can best match the settings to your weight and riding style. In our experience, the Mono Shock suspension is sprung fairly light, and many riders set the suspensions tighter than the specs indicate, especially for aggressive riding styles and or rougher conditions at higher speeds.
What this means is the Mono Shock rear suspension has a fairly limited range of rider weights that can be accommodated for any given calibration. Changing the suspension to accommodate a rider of a drastically different weight is many times not possible without shock removal, not feasible out in the field.