Fitting the Rear Fox Float X2 shock
The Fox Float X2 rear shock does not have a big steel spring, just air and oil to allow it to out perform the older heavy steal spring versions on downhill installations. It does come with two spacial costs. The high volume cylinder is big and the side oil can needs lateral clearance. Not all bike rear shock placement spaces even with mild modifications can accommodate this air-oil shock.
By mild modifications (2 types)
1. Drilling a new set(s) of anchoring holes on one or both frame fastening ends
A flat bar bell crank like on the Thumper can easily be drilled to make for additional shock mount locations. But some bell cranks are not suited to making other mounts.
2. Sometimes the frame structure supporting the seat tube is over designed and some surgical grinding of it metal to fit the oil can’s needed space can be done while still leaving plenty of seat support strength. Some grinding on the Broadie frame for the oil can clearance could be done and still leave adequate seat post strength.
There are some machine design programs that can be set up to do the kinematic analysis of the various shock assemble bars and projections of them to determine what set of drill holes will have clearance for the shock’s motions. One can do this graphically by hand.
Whatever mount holes you choose to use (existing or added) a new shock location will likely change the mechanical advantage [MA] of the lever that connects the shock to the upper stays. If you increase the MA you will need more air pressure to get the same initial loading sag [ suggested for Fox X2 20% - 30% of total shock travel].
My scenario: MA location giving shock clearance = 126% over lowest OEM holes’ MA. I chose an air pressure based on the rider weight plus all add-ons (motor, controller, batteries etc) = 210 lbs. The Fox tuning guide suggests an initial air pressure of 1 psi per pound of rider weight. To get 30% sag the pressure needed was 250 psi or about 1.26 x 200 = 252 psi. To get only 20% sag the shock air pressure needed was 300psi which is the shocks max suggested air pressure. So if you weight over 160 lbs you may have to settle for more than 20% sag, or find a shock mount that has a lower MA. The lower MA will convert your suspension to less wheel travel for a given shock travel.