^^ Plus even-even ratios are almost always abysmal for skidding, and bad (9 patches, unless i overlooked something) at best.

I like my 47t chainring; with 17, 18, 19t cogs i have 65, 69, and 73 inch gears available, all with very good skidding capabilities (17, 18, 19 patches respectively, * 2 when skipped ambidextrously) because 47 is prime and odd.

PS: I ride new surly cogs and haven't been able to dent em yet. they seem to be mighty good.