Nice one this, not unlike Pro Skateboard Sim, but more sophisticated and more addictive. The main difference, of course, is that you're riding a motorbike on this one, and scrambling around an extremely testing mountain course.
There's a time limit, natch, and the faster you complete the course, the more dosh you get to upgrade your machine. It's not terribly original, true - I mean, there's a virtually identical game on another part of this page - but above all it has been well designed. Your skill is always being tested, which can be a problem if you don't have any - but even I got the hang of things, so it can't be too difficult.
The programmers were Binary Design, who have done a lot of Mastertronic games, but this, I think, is one of their best. Neat stuff, and worth two nelsons of anyone's wad.