Doping

As andyp said earlier:

Ullrich's racing weight, on those rare occasions when he achieved it, was around 72 kgs.

Still, it's akin to him racing up Alpe d'Huez with a courier bag with a lock, a laptop, some tools and a morning's supply of buns on his back.

72kg is about 11 1/2 stone (~159 lbs.).

Of course, later he got heavier and turned up for the Tour at 76kg or more (I think).