Finally wide range 10 speed cassettes are on the market. IRD (Interlock Racing Design) is the forward thinking company that is making randonneur, tandem, and touring cyclists everywhere smile. The new rear cluster will require a long cage (mountain bike style) rear derailleur and will shift smoothly with Shimano 10 speed STI shifters. The downside of this modification is that the pricey cassette ($155+/-) does not shift very smooth. This is a worthy aftermarket purchase if having a wide range of gears in more important than a butter smooth shift.