I'm not quite sure what I did wrong/imperfect in my calculations, maybe I should have tried balancing around the highest points the cars reach rather than the center, maybe I underestimated the addition of new fast cars, but I feel like throughout the year we've seen a bit more of the faster cars than entirely justified by complete randomness and a bit less of some of the slower cars. (The BMW made the top 3 in 3 races, though never in first place, the Indy, 962, Audi DTM and kart made the podium in 2 races each. Not that I'm complaining, I like fast cars...)
In related news I feel like now we've reached the point where that imbalance has mostlty fixed itself. The cars that sat at too low a bonus to be viable this year also seem to have risen enough to stand a chance next year. The Jaguar sits near the other fast cars, The two Lambo's sit near the top (though they are slow enough that they could be there for a while). The Ferrari GTO does not have a stellar position but it is set up for one of the next two powergear races. The F40 probably got the rawest deal after all, that one might still be stuck in traffic for a while.
So far 6 races featured multiple cars in the top 3, 5 did not. Last year there were 3 mixed scoreboards, in 2017 2 and in 2016 none. Part of that is luck, but the system change does seem to be doing what it was supposed to do.
For next year we have to consider what to do with the monthly bonuses. We can keep them as they are, plus and minus 10 percents which are permanent. This means these bonuses have a big effect on when cars are due. On the plus side: the cars that people like come up more often. We can lower the amount the track maker can hand out as bonuses but keep it permanent. This lowers the size of the effect, but also the impact track makers have on how their track is run. The third option is to make the bonuses temporary. If the Indy sits at -6 and you give it +10 the bonus becomes 4 for the duration of the race, but it goes back to -5 for the next month (or less if the Indy ends up in the top 3). This option is probably the fairest one, and it gives track makers control over their track without big lasting consequences. On the downside it may encourage trying to set up 1 car races, just give +10 to your favorite car and yolo it. On the upside again, if that's your favorite car, why not?