For a camera that records continuously, the number that matters is sustained sequential write speed, and the marking that tells you about it is the Video Speed Class or UHS Speed Class symbol — not the big megabytes-per-second figure on the front of the package, which describes peak read speed and has almost nothing to do with recording. Get the class right, match it to what the camera supports, and treat the card as a consumable. Almost every dash cam storage problem traces back to one of those three points.
Reading the symbols on the card
There are four families of marking and they answer different questions. The SD Association defines capacity families first: SDHC covers cards over 2 GB up to 32 GB using FAT32, and SDXC covers over 32 GB up to 2 TB using exFAT. That single line explains why a 32 GB card and a 64 GB card sometimes behave differently in the same camera — the file system is not the same, and an older camera may only support the SDHC family.
Then come the speed markings. The SD Association's Speed Class page sets out the three relevant families: the original Speed Class marks C2, C4, C6 and C10; the UHS Speed Class marks U1 and U3; and the Video Speed Class marks V6, V10, V30, V60 and V90. Each guarantees a minimum sequential write rate under conditions defined in the standard, which is precisely the workload a dash cam produces.
The fourth marking is the one to ignore for this purpose. Application Performance Class, marked A1 or A2, measures random 4 KB read and write operations per second, because it was designed for cards holding phone apps and their data. Random access is not what a camera does. An A2 card is not automatically a better dash cam card, and paying for A2 while ignoring the video class is a common and expensive mistake.
Matching the card to the camera, and buying for endurance
Higher is not automatically better, because the card can only deliver its class if the camera's bus mode can carry it. The SD Association's bus speed overview sets out which bus each class needs — C10 runs in High Speed mode or faster, U1 and U3 need UHS bus modes, V60 and V90 need UHS-II or faster. A V90 card in a camera whose slot is UHS-I will simply run at UHS-I speeds, and you paid for headroom you cannot use.
The right approach is to read the camera's stated maximum supported capacity and minimum recommended class, and buy the smallest step above it that you can find easily. Buying two of those is usually a better use of the money than buying one card twice as fast.
| Decision | What to look at | What goes wrong if you get it wrong |
|---|---|---|
| Capacity family | Camera's stated maximum, SDHC versus SDXC | Card is not recognised, or works then corrupts |
| Speed class | Video Speed Class or UHS Speed Class symbol | Dropped frames, especially on fast-moving detail |
| Bus mode | What the camera's slot supports | You pay for speed the camera cannot use |
| Endurance | Cards marketed for continuous video recording | Premature wear from constant rewriting |
| Physical format | microSD versus full-size SD, and adapters | Adapters add a connection that vibration can disturb |
| Source | Reputable seller, sealed packaging | Counterfeit card that reports false capacity |
Cards sold for continuous video recording use flash designed to tolerate far more write cycles than the flash in a general-purpose card, because a dash cam rewrites the entire card every few hours it runs. A card that would last a decade in a camera you use on holidays can be worn out in a season in a dash cam.
The honest limitation is that endurance claims are hard to verify from outside, and the marking is not a formal SD Association class in the way Video Speed Class is. What you can do is treat the card as consumable regardless of what it claims: replace it annually if you ride most days, every couple of years if you ride occasionally, and immediately if the camera starts reporting errors or the footage starts stuttering after a fresh format.
Temperature, vibration and the motorcycle-specific bits
A card in a motorcycle camera lives somewhere a card in a car camera does not. Three practical consequences:
- Heat. A dark camera body in direct sun on a stationary bike gets hot, and flash memory does not enjoy sustained heat while writing. If your camera has a parking mode, that is the condition it operates in. Cards do have specified operating temperature ranges; check the manufacturer's figures for the specific card rather than assuming.
- Vibration. A microSD card in a full-size adapter has two connections instead of one, and the adapter is the weaker of them. If the camera takes microSD directly, use it directly.
- Moisture. The card slot is a hole in an otherwise sealed body. Closing the door properly is not optional, and a slot cover with a perished seal is a slow way to kill a camera. That is one part of the wider sealing question covered in waterproofing and IP ratings explained.
Counterfeits, wear, and the signs a card is going
Fake high-capacity cards are common and they are convincing. The usual trick is a small card reprogrammed to report a large capacity, so it appears to accept files and then silently discards or corrupts anything written past its real size. In a dash cam this is particularly nasty, because loop recording means you never look at the old footage until you need it, and by then it is gone.
Two defences. Buy from sellers you would trust with a warranty claim, and verify a new card before it goes into service by filling it with test data and reading it back. Any capacity-verification tool will do this; the point is to find out on your bench rather than after an incident. It costs an hour once per card.
The pricing signal is worth reading too. Card prices track capacity and speed class fairly predictably, so a card advertised well below what comparable cards from established brands cost is telling you something. It might be old stock or a genuine clearance. It might also be a card that will report a capacity it does not have. On a component whose whole job is to still be working on the day something goes wrong, the saving is not where you want to take a risk.
Cards rarely die cleanly. They degrade, and the early signs are easy to blame on the camera:
- Footage that stutters or smears on fast detail, and keeps doing it after a fresh in-camera format.
- Segments that are shorter than the loop length you set, because the write stalled and the camera closed the file early.
- Files that appear in the list but will not open, or open with the last few seconds missing.
- The camera taking noticeably longer to start recording after power-on.
- Occasional error messages that clear themselves on a restart.
Any two of those together is enough. Swap in a card you know is good and see whether the behaviour follows the card or stays with the camera — that one test separates a worn card from a camera fault in ten minutes and saves a lot of guessing.
Formatting, and the routine that keeps speed up
Format the card in the camera before first use, and periodically afterwards. The camera writes the folder structure and file system it expects, and formatting clears the fragmentation that continuous overwriting builds up. The SD Association notes that repeated deletion and writing gradually fragments the data area, that fragmented writing is slower than sequential writing, and that reformatting may be needed to restore rated performance. For a device that does nothing else, that is a maintenance item rather than a one-off.
Everything you want to keep has to come off the card before you format it, which is the point of having an offload routine at all. Ours is set out in motorcycle dash cam file management, and the mechanics of what the camera is doing while it writes are in loop recording explained.
One last trade-off worth stating plainly. A very large card gives you more days of history and takes longer to check, longer to offload and loses more when it fails. Two mid-size cards on rotation give you a spare on the road and a natural point to archive. Neither is wrong, but the second one fails more gracefully. If you are still choosing the camera itself, the comparison is in the motorcycle dash cam guide, and a sealed motorcycle camera body protects the card slot as much as the electronics.
FAQ
What speed class do I need for a motorcycle dash cam?
Follow the camera manufacturer's stated minimum, and read the Video Speed Class or UHS Speed Class symbol rather than the headline megabytes-per-second figure. Those classes guarantee a minimum sustained write rate, which is what continuous recording depends on.
Is an A2 card better for a dash cam?
Not for recording. Application Performance Class measures random 4 KB operations per second, which suits phone apps. A dash cam writes long sequential streams. Choose on video class and treat A1 or A2 as irrelevant to this use.
How long does a memory card last in a dash cam?
Months to a couple of years, depending on hours recorded, because loop recording rewrites the whole card repeatedly. Replace it on a schedule rather than waiting for it to fail, and replace it immediately if footage stutters after a fresh in-camera format.
Can I use the microSD card from my phone?
You can, but it is the wrong tool. General-purpose cards are not built for continuous rewriting, and a card that has already spent a year in a phone has unknown wear. Buy a card for the camera and leave it in the camera.
Why does my camera reject a large card?
Most often because the camera supports the SDHC family only, which tops out at 32 GB and uses FAT32, while the card is SDXC using exFAT. Check the camera's stated maximum capacity before buying, not after.
