This is going to be a short 'guide'.

The reason I'm making it is because designing cars without limitations is just boring. At the same time any challenges and competitions out there are pretty arbitrary, so I decided to go with official regulations that exist to balance the performance of the cars taking part in the races.

I compiled a list of various racing series regulations (far from complete, but I will be updating it). These come from open sources available to me, previous Automation challenges and a bit of my arbitrary judgement:

https://docs.google.com/spreadsheets/d/1dJ3z8LlJ8S4FzZZdRM8vkzXln1GL3wOC/edit?usp=sharing&ouid=106264211467113902559&rtpof=true&sd=true

Please feel free to use these in your creations, challenges and for whatever other reasons.
Any feedback on accuracy and improvement is also welcome.

Update 1.1: added Group R-GT and Group B Rally classes - both have very few limitations compared to others and allow for some crazy builds.
Update 1.2: added SCORE regulations for Baja cars and trucks. Though the official regulations don't put a limit on type of fuel, I still did so that engine size limitations make actual sense.
Update 1.3: Group A Rally and WRC now have restrictions on Intake air flow (basically size), not turbine inducer size; Group A Touring has increased max cost and max quality restrictions - same as in GT3 to allow for better replicas of original Group A cars.
Update 1.4: Added DTM - early (V8) and late (I4 Turbo) specs - basically a less strictly regulated GT3. The division by years is approximate, as changes occured gradually over time. Will try and get BTCC next. Engine stress limits will also be revisited some time in the future, likely after the current release is out of beta.