SD Card Speed Classes Explained
When buying an SD card, you’ll see speed class markings on the label: a number inside a circle (Class 2, 4, 6, 10), a U with a number (UHS Speed Class 1 or 3), or a V with a number (Video Speed Class). These ratings indicate the minimum sustained write speed the card guarantees.
- Class 10 / UHS-I: Minimum 10 MB/s write speed
- UHS Speed Class 3 (U3): Minimum 30 MB/s write speed
- V30, V60, V90: 30, 60 or 90 MB/s minimum write speeds for video recording
Does Speed Class Matter for Car Navigation?
For factory car navigation systems, speed class matters very little in practice. Navigation systems read map data from the SD card — they don’t write to it during normal use. Speed class ratings describe write speed performance. Read speeds on even a Class 4 card are more than adequate for the data throughput that a car navigation system requires.
A factory sat nav loading a map tile or recalculating a route is drawing a modest amount of data from the card — nothing close to the throughput demands of 4K video recording, which is what the higher speed classes are designed for.
What Actually Matters for Nav Cards
- Compatibility — correct format (full-size SD, not microSD), correct capacity for the map data
- Map version — the data on the card needs to be current and correct for your region
- Reliability — quality flash memory that won’t corrupt or fail after years of in-car use
- Temperature tolerance — car interiors can reach high temperatures; quality navigation cards are rated for extended temperature ranges
Why You Can’t Use a Blank SD Card for Navigation
Factory navigation SD cards are supplied pre-loaded with licensed map data configured specifically for the navigation system they’re designed for. You can’t simply buy a blank SD card and load maps onto it — the system requires licensed data in the correct format and file structure, which is what a genuine navigation update card provides.
Dash Cam SD Cards: Where Speed Class Does Matter
Speed class matters significantly for dash cameras, which write video continuously. A dash cam recording 1080p or 4K footage needs a card with a high enough sustained write speed — typically U3 or V30 as a minimum for 4K. Using a slow card causes dropped frames, file corruption and recording gaps. This is a completely different use case from navigation.