1. A medium cost, accurate and practical way to get coast down data is to connect a $40 Wahoo wireless bike speed sensor to some rotating part of the car and to collect downloadable data with the $80 Wahoo Ant+ Key connected to an iPhone. Any Garmin sports watch or bike computer can also record the wireless speed signal. Downloadable is the magic word here.
2. With proper understanding of the physics involved and a clever protocol/analysis, accurate Crr and CdA can be calculated.
3. GPS data is way too noisy for this.
4.
Estimating drag without a power meter: Triathlon Forum: Slowtwitch Forums