A car already records the seconds before a crash, and none of it is video. 49 CFR Part 563 requires a vehicle equipped with an event data recorder to capture indicated vehicle speed, throttle or accelerator position and service brake on-off from 20 seconds before time zero to time zero at 10 samples per second, and longitudinal delta-V for the first 250 milliseconds at 100 samples per second. A phase-in in that same table lets vehicles built before September 1, 2031 record the pre-crash elements from 5.0 seconds before time zero at 2 samples per second. What a dash cam adds is the picture, and the figures that decide it are resolution, field of view and the card. The condition that changes everything else is parking: a camera that records while parked needs constant power and a much larger write budget.
The EDR records numbers, the camera records a scene
Part 563 also dictates what the owner is told. Under Section 563.11, the owner's manual of a covered vehicle must state that the EDR records for a short period, typically 30 seconds or less, that no data are recorded under normal driving conditions, and that reading the data requires special equipment and access to the vehicle. Section 563.10 requires the recorded elements to survive the crash test and remain retrievable for not less than 10 days afterwards.
So the gap a dash cam fills is narrow and specific: what the other vehicle did, what the lane markings looked like, and what the light was. Numbers about your own car already exist. That distinction decides what resolution is worth paying for, because reading a license plate is the job that resolution buys.
Resolution and field of view trade against each other
A wider lens spreads the same pixels over more scene, so the two figures have to be read together. Garmin's 2021 announcement of the Dash Cam series publishes both for four models:
Scroll sideways to see the full table →
| Model | Resolution | Field of view |
|---|---|---|
| Dash Cam Mini 2 | 1080p | 140 degrees |
| Dash Cam 47 | 1080p | 140 degrees |
| Dash Cam 57 | 1440p | 140 degrees |
| Dash Cam 67W | 1440p | 180 degrees |
The 67W is the pair to study: Garmin states that its extra-wide 180-degree lens captures cross-traffic detail, which is a different job from plate reading at distance. The 57 keeps the same 140-degree field as the cheaper models and raises resolution instead. Garmin's series prices in that announcement run from $129.99 to $259.99.
Frame rate is the third figure and it is a genuine trade. Garmin's owner's manual for the 47, 57 and 67W lists the selectable settings: 1440p at 30 frames per second with HDR and 1080p at 60 frames per second on the 57 and 67W, 1080p at 30 frames per second with HDR and 720p at 30 frames per second on all three. At 1920 by 1080 pixels, the 60-frames-per-second setting doubles the frames a second but records fewer pixels in each of them than the 1440p setting does, and the manual notes that a higher resolution or frame rate uses more card space.
The memory card is the consumable
Dash cams write continuously and overwrite constantly, which wears cards out. Garmin's manual specifies a microSDHC or microSDXC card of 8 GB or greater at speed class 10 or higher, and instructs that the card be formatted at least once every six months to extend its useful life. It states plainly that all microSD cards wear out after being overwritten a large number of times, that a higher-capacity card is overwritten less often and usually lasts longer, and that the camera deletes the oldest unsaved video automatically when the card is full.
Budget for a replacement card on a schedule rather than after a failure. The same manual says the device detects card errors and alerts the owner when it is time to format or replace, which makes the alert a maintenance item, not a fault.
Cloud storage is a subscription
Saved clips go to Garmin's Vault over Wi-Fi. The owner's manual states that videos are stored in the Vault for up to 24 hours with a Garmin Drive account and that an optional Vault subscription, purchased in the app, extends that storage time; Garmin's announcement gives the extended option as up to 30 days, which is thirty times the free window. Nothing about that is unusual for connected hardware, and it is the same arithmetic that decides what a video doorbell costs over five years.
The figure to compute is the subscription's yearly price multiplied by the years the camera will be kept, added to the purchase price. A camera that keeps everything on its own card has no such line; it also has no copy of the footage if the camera leaves with the car, which is the trade being made. Drivers who also run an e-bike or park where power is available should price the parking mode cable separately, since constant-power recording is a wiring job, not a setting.
Before you buy a dash cam
- The resolution and the field of view in degrees together, since a wider lens spreads the same pixels further.
- The frame rate options at each resolution, from the owner's manual rather than the product listing.
- The card specification the manufacturer requires: Garmin asks for microSDHC or microSDXC, 8 GB or greater, speed class 10 or higher.
- The manufacturer's formatting and replacement schedule for the card, which for these Garmin models is a format at least every six months.
- The free cloud retention and the subscription price for longer retention, multiplied by the years the camera will be kept.
- The parking mode power requirement and the cable or hardwire kit it needs, priced as part of the installation.
- The warranty document, and what it says about the included memory card.