The GT Tachyon was the first GT bike with drop bars. It has a number of features that make it a great allrounder.
Here’s a couple of articles with plenty of background.
http://www.retrobike.co.uk/forum/viewtopic.php?t=237517
http://sfcyclotouring.blogspot.com.au/2008/05/gt-tachyon-great-idea-that-happened-too.html
Size is 54cm
