Smaller drive sprockets gain additional clearance for deep lug tracks. For track clearance, measure from the top of the track paddle to the bulkhead (smallest clearance area), then add the extra paddle height of the new track (i.e.. 1" to 1.5" is an extra 1/2). After installation of new track, 1/2+of clearance is still required for track deflection while driving. EXAMPLE: 1" clearance with 1.25paddle track and a 9 tooth sprocket. New track has a 2" paddle, which leaves 1/4" of clearance which is insufficient. Installing an 8 tooth sprocket gains 7/16" of clearance which will add upto 11/16" of clearance (7/16" + 1/4), which meets the proper clearance recommendation. Upper chaincase gearchange may be required for proper gear ratio.