'Novice', or 'D grade', is generally used when there's enough participants.
We use the rule of thumb that 'if you finish on the same lap, you're in the right grade' - ie, if you don't get lapped, or you're not lapping riders.
Similarly if you're in a grade and you're going to finish in the top 50% of the grade above, you're a massive sandbagger. If you're in a grade and 50% of the grade below you are quicker, you're probably in too high a grade. Anywhere in between, and you're about right.
From my experience, 'Sport', being the state level and higher open level category, should really be a pointy-end-of-C-grade level of competition. In the early years I was racing, this held true - back in 2007, we really on had one obvious, massive sandbagger - the rest of the field was pretty evenly matched at the front. But in the years since we're been seeing A grade club riders still racing sport at state level. As a rule of thumb, in an evenly matched, fair race, Sport should be about 50% slower than the winning Elite riders. eg, when Jongewaard and Norris were doing 14s at Glenorchy, myself and the others were doing 21s, and it was a reasonably well-matched race. Lately though, we're seeing riders enter Expert at state level who at times have had average speeds that put them top 3 in Elite. That means the guys in Sport are still getting lapped, and lapping others in the Sport field. That's not cool at all.
It really shouldn't be a hard concept:
Club A: Elite
Club B: Age categories
Club C: Sport
Done.
All you guys who want a Singlespeed Rigid 29er category, instead we might direct you to the nearest local bike store
What I really don't subscribe to is this idea that you need a category for every four riders.
Once a category has 30 riders, then we can look at splitting it. But not before. If you want to win, you have to actually beat someone. And if you really care about winning, then isn't beating two others a pretty hollow win?