A dash cam is the only device most people own that writes to flash memory every second it is powered. That workload is unlike anything a camera or a phone does, and it is why storage is the most common point of failure in the category.
Why ordinary cards die
Flash memory cells tolerate a finite number of write cycles. A dash cam recording in a loop overwrites the same card continuously — many terabytes of writes per year in normal use.
A standard microSD card, designed for occasional photo storage, reaches the end of its endurance quickly. Symptoms in order: corrupted individual files, then failed recordings, then a card that reports as full or unformatted.
High-endurance cards are the answer
Cards marketed as high endurance or for surveillance use memory rated for sustained sequential writing, and manufacturers publish an endurance figure in terabytes written or in recording hours.
That published figure is the specification to compare. A card quoting “up to 20,000 hours of Full HD recording” is telling you something useful; a card quoting only a read speed is not.
Speed class also matters, but less than people assume. U3 or V30 is sufficient for 4K dash cam recording, and paying for faster classes buys nothing here.
The silent failure problem
This is the part that costs people evidence. A failing card frequently does not produce any warning on the camera. The screen shows a recording indicator, the timestamp advances, and nothing is written.
Owners discover it at the worst possible moment, months after the card actually failed.
Treat a dash cam as untested until you have played back footage on a computer. Not on the camera’s own screen — on a computer, where you can confirm the file exists, opens, and is sharp enough to read a plate.
A maintenance routine that takes five minutes
- Format the card in the camera every one to two months. Formatting in the camera, not in a computer, aligns the file system to how the camera writes.
- Play back a recent file on a computer at the same interval. Confirm a stationary number plate is legible.
- Replace the card annually in heavy use, or when the camera reports errors. Cards are inexpensive compared with what they are protecting.
- Check the camera is on after any time the car has been left for a long period.
Loop recording and how much you keep
Loop recording splits footage into segments — one, three or five minutes — and overwrites the oldest when the card is full.
- Shorter segments are easier to extract and share, and lose less if one file corrupts.
- Longer segments produce fewer files to sift through.
Three minutes is a reasonable default. Card size then decides how many hours you retain before overwriting. From a data protection perspective, keeping less is easier to justify than keeping months of footage of everywhere you have driven.
Protected files and the G-sensor trap
An impact triggers the G-sensor and marks the current file as protected, exempting it from the loop. That is the feature working correctly.
The trap is sensitivity. Set too high, every pothole and speed bump protects a file. Protected files accumulate until they fill the card, at which point loop recording stops entirely and the camera records nothing new.
Set the G-sensor to a middle setting, and clear old protected files when you do the monthly check.
Capacity, briefly
- 32 GB: a few hours of 1080p. Adequate for a commute, tight for 4K.
- 64 to 128 GB: the sensible range for most single-channel cameras.
- 256 GB and above: worthwhile for two-channel 4K systems, provided the camera supports the capacity — many have a stated maximum, and exceeding it causes exactly the silent failures described above.
Check that maximum before buying a large card. It is in the manual, rarely on the box.
