A TT bike will usually has a shorter top tube. Your friend is correct in
that regard. How much shorter? This depends on your unique body measurements
and flexibility, the angle of the seat-tube (among other things). This also
assumes you are already riding the correct size road frame. A TT fit is much
different than a road fit. Measurements from your road fit will help you,
but it's different for sure.

RC
--
Russell Cree, DPT, CSCS
Herriott Sports Performance
www.herriottsportsperformance.com
206.306.5899