The +/-10mm head covers the heart of the tri range, at least as generally accepted here on Slowtwitch, from about 78-81 effective STA, with the saddle more or less in the middle of the rails. It is not likely to get you to a UCI-compliant 5cm saddle-nose-behind-BB position, though. Early users (like istanford) who did need to get there found they needed the +/-35mm head mounted rearward and saddle slammed all the way back on the rails. Conversely, with some saddles like the ISM Adamo you may not be able to get the post into your favorite steep tri position when using the 35mm in either orientation, and this is when the 10mm is called for. The heads are available separately through your Trek dealer in case you want or need to have both on hand.

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Carl Matson