Hey Joe,

The road from Akatarawa Saddle in should be pretty manageable on a bike, its steady but not really steep any place - and Renata hut, though basic is a much nicer place to stay than Waiotauru (which is just an old bulldozer shed). I've been to both, though not done the track in between - it must be pretty good though, as last time I was at Waiotauru there were two Hiluxes in there, so you shouldn't have any trouble getting a mountain bike that far at least if you wanted...

I also haven't done Renata Ridge, but by all accounts its quite a long way... Elder hut is a nice new 4 bunker though.

Hope this helps anyway, happy tramping/biking!