[X25]

Based on your responses, I'm guessing you think I'm bashing GPS over OBD speed data? That's not my intent; they're both very valuable.

I log them all, and use whatever works best if I need to analyze something. I already 'synchronize' the GPS data with the OBD data, but even when you make it perfect, the GPS transponder will sometimes 'delay' the update. In my experience, compensating for that delay often created negative artifacts elsewhere.

You should definitely use OBD speed data for the speedometer gauge, since even when perfect, GPS speed will be very much off in any long turn. I care about my speed mostly at the entry to, or at the end of straightways (where GPS is correct), and care about my speed data for the whole corner. Using only GPS data would be very misleading in long sweeper corners, and you could have wrong conclusions : )