A lot of competition 2-strokes use only one ring. I believe the particular profile of the ring was known years ago as a "Dykes" type.
The illegal trick is to either allow the second ring to become stuck in it's groove, or reduce it's natural spring to lessen it's contact with the bore: It's rumored that a well-known TKM tuner (Who shall remain nameless) was caught doing this.
The sealing effect of the top "Dykes" type ring is so effective that any advantage of the second ring's extra sealing is outweighed by friction caused by contact with the bore: particularly at high revs.
The Extreme engines have only one ring, and I suppose, that Tal-Ko have seen the obvious financial savings in producing pistons with only one ring instead of two.
The savings in costs of manufacture, will I'm sure, be reflected in the price of the new pistons. :) Dave.
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