Nobody?

 You get all golds in 100cc, or something like that.

 That's the bike you always use. I hadn't really noticed you still used the Nitrocycle, I thought you would have changed by now. I can't tolerate it's terrible drift myself, it is almost as bad as using the Torpedo (the equivalent bike in heavy class)

I originally couldn't get used to the hugging drift that the faster bikes do, which was why I used the standard bikes that perform a sliding drift.... so I used to always be Rosalina on the standard bike L, then when I started doing time trials properly I forced myself to get used to the bowser bike/torpedo, and now I find it hard to race with a 'sliding' bike or a kart.
Recently I changed to the mach bike because of the horrible acceleration from the Bowser bike, but in hectic races against other skilled racers like Just_Ben, etuoyo and yourself I am not sure it has enough acceleration, so I may be changing again if I can find a suitable one.

I may check out the Magikoopa shaped one as it proved absolutely brilliant for the two tracks I stuggled on with Bowser Bike, those being Sherbet Land and the GBA Beach one. I hate being pushed around though so being light might annoy me too much. (case in point there were two instances I was knocked off the track by someone in the last GPs)

 Based on the description from TWRoO's link

Nitrocycle - Attain at least a 1 star rank in all 100cc Wii Grand Prix cups:

I don't have that yet. I have 2 or 3 stars in every 50cc and almost 1 star in every 100cc. I have all golds in 150cc but only a couple stars. I haven't played the mirror tracks yet.

Once I am decent on brawl I will try get good on Mk wii *Looks at RolStoppable*you will be stop once I start playing that game.

@superchunk. I don't think Mirror tracks count for most unlockables, so getting 1 star ranks up through 150cc will be enough.