The Shallow Cone Cup is a solution for Trek Speed Concept frames requiring a smaller outside diameter cone cup on the drive side of the trainer than the pre-installed cone cup. While the Small Cone Cup (pre-installed on trainers manufactured after December of 2009)* will fit into the speed concept carbon frames, it does rub on the drive side. So, making a cone cup that has a smaller outside diameter fits better and prevents the carbon from getting marred.
*The small cone cup will fit the aluminum framed Speed Concept series bicycles, but we recommend using this specially-machined cone cup on carbon-series bikes. This cone cup will clear the frame flange and not mar the carbon. Use this cone cup on the drive side (side with chain) of the trainer. Replace only the drive side cone cup on the trainer. It is not necessary to replace both cone cups.