From Grand Theft Wiki
A Double T in The Lost and Damned.
The Double T is a new bike in The Lost and Damned and The Ballad of Gay Tony for Grand Theft Auto IV.
The bike is most likely based on a Kawasaki Ninja ZX-10R. The Double T is probably the slowest of all six new street bikes, being slower than the Hakuchou. The Double T can be found around parts of Northwood, driven by the Uptown Riders, and available to obtain by calling Clay, although after a certain mission.
The Double T Custom is a more powerful variant of the Double T with a bit different model and vinyls. The custom version is considerably more stylish and faster.
The Double T does reappear in The Ballad of Gay Tony but can only be found in Alderney, but most common in Alderney City.