Hello,
at firtst I must say, that your physics model makes this game better than anything else out there and I am comming back to this game for many years now, but I keep leaving the game too. It is because its online system - you are heavily missing few things, mainly iRacing like races (one race is started like 100 times per week, you can join whichever you want and how many you want and at the end of the week, your 2 best races are averaged) and matchmaking.
In real world, I would start by racing gocarts (which are "slow" but they have small track too, and they are raced by other amateurs), in LFS i have to start with hatchback, which is boring as hell and I still manage to be one of slowest guys on server, because many "pros" keep racing it and one lap takes almost 2 minutes, but has like 10 corners (Blackwood).
If you were to track "avg of last 10 laps with car a on track b" and averaged it and that time per person used as "skill" and then, if you were to provide some stable races, which will start several times a week, but will be "one race" (iRacing), and if you were to matchmake players primarily from same group (or you can just order 30 people signed for race by their skill and then have 3 different starts, 10 worst players, 10 medium players and 10 top players of that group), it will be a gamechanger.
Basically every online racer is missing good matchmaking system, but in this genre, it is absolutelly crucial - if you are 3s slower per lap, you are not racing, you are driving "hot lap" while others are racing. (However, if you are lame FPS player, you still get lots of fun playing against "pros" in Quake, because even if you loose by score, you will manage to get some kill)
Now this is based on population of server, so I sugest that you implement those mechanisms and start just one league, which can be track a week style, and have 3 different car types mixed race, will be launched on like 5 servers which will be filled by "skill" order and in time you will see, how much popular it becomes and you can add more leagues then or cancel even that one...
I don't know, how you like that idea, but frankly, your actual system is not really useable for casual gamer, which just likes good car physics and that is heavy underseller of the game. I don't want to play iRacing, I hate their snap-slide braking, their little oversteer=360° slide because we cannot simulate drift etc. and this is basically problem with every other race game, except LFS.