Rainier is awesome for riding.
There are four loops you can ride but fuel is not so easy to find. I usually fill up in Enumclaw or Ashford depending on what direction Im going around the mountain.
You have to stop for pie at the Copper Creek Inn at the south end on Ashford.
Take the side route over to Sunrise, well worth it for the ride and scenery.
Mind your speed as this is a national park area (animals and authorities).
Last time I rode the big loop the roads were good but needed some maintenence.
We rode to Mowich Lake (Carbon River Ranger Station) last time also... that was nice scenery. A different view of the mountain than normal. Again, not a fast road but nice.
Link to Map