OBD-II or direct CAN: two very different access levels. The real work is reversing the DBC. The right adapter depends on the vehicle, stock or competition.
Reading a vehicle’s data in real time happens at two levels. Mixing them up leads to poor or unreadable data.
OBD-II versus direct CAN
The OBD-II port exposes a standardized subset through simple requests: engine speed, road speed, engine load. It is portable across brands but limited, and polling is slow against the internal rate.
The direct CAN bus carries all the controller traffic, raw and far faster. You read there what the maker does not expose. In return, nothing is documented: each message is a byte string with no public meaning.
DBC and adapter
The real work is reversing the DBC, the file that decodes each CAN frame into named signals. Without it, the bus is just a byte stream. With it, it becomes usable telemetry.
The adapter choice follows the vehicle. On a stock car, an OBD-II reader covers the basics. On a competition car, you tap the direct CAN, with a fast interface and a DBC already reversed or to be rebuilt.