I use a speedometer mod that measures in it. Looking at the code, from what I understand it’s essentially getting the player’s velocity value and multiplying it by two. I also have another speedometer mod that measures in several different units of your choosing, including TPS, BPS, MPH, and KMH.
So the maximum speed achievable by default is 200 BPS, which is 100 TPS, pretty much exactly 155 MPH, and just a little under 250 KMH.
Whatever your car’s maxWheelSpeed is set to, as well as any other speed-related parameter (like the gear shift speeds for the engine sound configuration), is half of BPS. But setting the maxWheelSpeed value higher than 100 provides no difference to handling, it just makes the car accelerate faster and then peak at 200 BPS.