Waht bike are we talking about here, is it the ordinary bike, or a race bike am just wondering, because if we are talking of cycling i don't know how long that will take from whichever side you are coming from. Anyway i guess from Nairobi it may not seem so hard with a race or motor bike, given that you will not be cycling, that makes the journey much easier. i guess you can access it from three different routes, there is the route from Busia going through Uganda then to Tanzania, or you can use the namanga border, i think the other route is through a game park, though not so sure about it. The one i know would work pretty well, is through Namanga and i have have used it before not riding obviously, but it's not as bad, apart from a few rough patches here and there it is more user freindly. there aren't too many cars on the road either.