The Tasman River Track is a 25 km out-and-back jittery gravel four wheel drive track that goes up the eastern side of the Tasman River from the top of Lake Pukaki.
It is part of the Alps to Ocean trail and is one of several tracks described in the Department of Conservation's "Mountain Biking in Mackenzie/Waikato". You can pick up this little booklet for $2 at local information centres.
As you ride up this trail you get good views of Mount Cook and other mountain peaks. But if you really want to feel the magic of these mountains go to Mount Cook Village and walk some of the tracks there. And if you want a local ride that is much more fun try the Twizel River Trail.
The Tasman River Track is pleasant enough but certainly not worth the 82 kilometre out and back drive to get to it.