Hey,
This will be short. I want to share with you all a very nice website that speaks about all things GTA-5 cars in great depth.
Did you know that neons and exhaust tips significantly affect your car's centre of mass and subsequently it's handling/on-road (indirectly) performance? You do now.
Such a resource will probably come as a "thank you, captain obvious" to many, but I'm sure a good bit of people will appreciate it.
The website offers, like already suggested, in-depth explanations when it comes to vehicle modifications and how they truly can affect a vehicle. It contains spreadsheets with real-top speeds and literally everything.
I take absolutely ZERO credit for this. Just sharing the love. Now and without further to do:
https://broughy.com/gta5carupgrades
Picture for effect: