The dual drive on my other Twenty "Grace"... it gives me a great 6 speed gear range (32-72 gear inches) and no overlap with 12.5 % jumps between gears.

Since the chain ring on a P20 is a 3/32 I used 2 Shimano 3/32 cogs (16/18) in place of the 1/8 SA cog and spacers, used a Suntour derailer, and a thumbie to handle the rear shifting duties. Some small modifications had to be made to the d hanger to get it to work well.

I took her on a group ride a few weeks ago and folks were having trouble hanging on to my back wheel on some steep climbs where I never had to get out of the saddle and could spin my way up which was good since I am not up to standing climbs yet.

She's nearly as fast as her partner.