Firstly, thanks a lot for taking the time to produce this app, I can't imagine how much time went into it. I've been driving sims since late 1970's (who remembers the intellivision ? 🙂 and a big part of my enjoyment is hot lapping so I think your app has great potential.
My suggestion for a level playing field is to let people setup the car however they want. Whether its driver aids, fuel levels, and so on.
However, to counter this, and for those that don't know, give a brief overview of what is generally accepted as the optimum settings. Since CM allows saved custom pre-sets it is very easy to set tyre wear to 0, fuel consumption to 0 and ideal weather conditions with one click.
With regard to driver assists, in my experience these tend to ultimately slow you down when you have learnt how the car handles, traction control being a prime example. But by allowing these it gives the less experienced driver, or perhaps those using a controller, a chance of competing.
The same for fuel, whilst 1 litre will make the car lighter, sometimes older cars handle better with a bit more fuel for ballast.
I would argue putting the onus back on the driver to find what works for any particular car instead of a bunch of server side rules will ultimately make it more fun, flexible and customised for each driver/car.
Of course just my opinion !