Why does my dashcam keep killing SD cards?

Because continuous recording is a write firehose. A 1080p cam at 15 Mbps writes about 162 GB every day and ~59 TB a year, non-stop, often in a cabin above 60 °C in summer. A normal consumer card is built for occasional photo bursts, has little spare area for wear-levelling, and no power-loss protection — so it wears out or corrupts in months. The fix is an endurance-grade card rated for sustained writes, not a faster or bigger consumer card.

How many hours of footage fits on each capacity?

Use GB/hour = bitrate (Mbps) ÷ 8 × 3.6. At 1080p/15 Mbps that is ~6.75 GB/hour, so a usable ~119 GiB on a "128 GB" card holds about 17 hours before the loop overwrites. 256 GB ≈ 35 hours, 64 GB ≈ 8–9 hours. A dual-channel (front + rear) cam writes roughly double the bitrate, so halve those numbers. 4K at ~40 Mbps is ~18 GB/hour — about 6.5 hours on 128 GB.

Do I need A2, V30, or both for a security camera?

V30 (= U3, 30 MB/s sustained write) is the floor that matters — it guarantees the card keeps up with the stream. A2 is the Application Performance Class for random app I/O and is irrelevant to a single sequential video stream; do not pay extra for it on a recorder. Above the V-class, what actually protects you is the endurance grade and a wide temperature rating, not a bigger A number.

Choosing a microSD for dashcams and security cameras (and why the last one died)

The card in a dashcam or security camera has the hardest job in consumer flash: it writes, all day, every day, often in a hot cabin, forever. Treat it like the card in a phone and it dies in months — and you find out at the worst possible moment, when you go to pull the clip that mattered and it's corrupt. None of this is bad luck. It's arithmetic, and once you see the numbers the right card is obvious.

Why consumer cards die here — the write load

Start with how much data continuous recording actually writes. The conversion is:

GB/hour = bitrate (Mbps) ÷ 8 × 3.6

A typical 1080p dashcam runs around 15 Mbps. That's 15 ÷ 8 = 1.875 MB/s, or about 6.75 GB every hour. Run it 24/7 and you get:

~162 GB per day
~59 TB written per year, non-stop

A consumer microSD is designed for bursts of photos and the occasional video — modest total writes, lots of idle time. Pointed at a 59 TB/year firehose, with little over-provisioning for wear-levelling and no power-loss protection, it wears out or corrupts in months. Heat makes it worse: a parked car in summer easily passes 60 °C, well outside a consumer card's comfort zone. This is the same consumer-vs-endurance split we cover in high-endurance vs consumer microSD; a recorder is exactly the workload that exposes it.

Lifespan is just division

Endurance cards publish a TBW (terabytes written) or a rated number of hours, derived from a standard workload method [3]. Once you know the yearly write load, lifespan is one line:

Lifespan (years) ≈ card TBW ÷ yearly write (TB)

At ~59 TB/year for 1080p:

Card	Rated TBW (128 GB class)	Lifespan at 1080p (~59 TB/yr)
Consumer card	not rated (low)	months
High-endurance	~700 TBW	~12 years
Premium endurance / pSLC	higher still	longer

Now switch to 4K at ~40 Mbps: that's ~18 GB/hour, ~432 GB/day, ~158 TB/year — roughly triple. The same ~700 TBW card now lasts about 4–5 years, not twelve. Resolution and dual-channel both multiply the write load, so they divide the lifespan. This is why "buy a bigger card" doesn't help endurance — capacity and TBW are different axes.

Size capacity to the recording loop

Capacity decides how many hours of loop you keep before it overwrites — not lifespan. Using the same GB/hour figure and a card's real usable size (a "128 GB" card is ~119 GiB — see why 128 GB shows 119 GB):

Capacity (usable)	1080p single-channel (~6.75 GB/h)	4K (~18 GB/h)
64 GB (~59 GiB)	~8–9 hours	~3 hours
128 GB (~119 GiB)	~17 hours	~6.5 hours
256 GB (~238 GiB)	~35 hours	~13 hours

A dual-channel cam recording front + rear writes roughly double the bitrate, so halve every figure. Pick capacity for how much continuous history you want to keep; pick endurance for how long the card survives. They are separate decisions.

What to actually buy

For any recorder — dashcam, CCTV, NVR with local card, body cam — the spec sheet should show, in order of importance:

An endurance grade with a number. A stated TBW or rated recording hours, not just the word "endurance" on the label. If there's no number, treat the claim as marketing. (And verify the card is genuine before trusting any of it — how to test for fake capacity.)
V30 / U3 speed floor — guarantees the card keeps up with the stream. Higher V-classes only matter for very high bitrates or many channels. (What the markings promise: speed classes decoded.)
Wide operating temperature, ideally -25 to 85 °C, for hot cabins and outdoor enclosures.
A concrete warranty term (years), not a vague "lifetime."

Note what is not on that list: A2. The Application Performance Class is for random reads and writes when a card runs apps or an OS — it does nothing for one big sequential recording stream, and paying extra for it on a recorder is wasted money.

Bottom line

Continuous recording writes tens of terabytes a year, so the only spec that decides whether your card survives is endurance — a published TBW or rated hours — backed by a V30 floor and a wide temperature range. Size capacity separately, to the hours of loop you want. Skip A2. And confirm the card is real before you rely on it, because a counterfeit fails fastest exactly where it matters most. Tell us the camera, the resolution and how many channels, and we'll spec the endurance grade and capacity to match — every card 100% capacity-tested, with the rated TBW stated up front.