I need dual pucks because the 21" tires are much harder to stop than 6" or 8" tires. No mystery here but edges of the gear need to filed down to allow clearance for the brake calipers. Also since installing two sets, there is an additional area about 2" up from the bottom on the aft side of the gear which must have about 3/16" of material removed.
So after getting these installed I removed them until later and installed the tires. First packed the inner and outer bearings with grease approved by Matco.
