MicroSD card speed drops through a hub? Check it

Your microSD card reads or copies files much more slowly when its reader is plugged into a hub. The hub may be sharing bandwidth with other devices, but the reader, cable, card, or USB port could also be the cause.

Compare the same card through the hub and connected directly to your computer. The USB & SD Speed Test measures real read and write speed, so the comparison can help you narrow down where the slowdown starts.

Compare the card through the hub and directly

Back up important files from the microSD card. Close file transfers and apps that might be reading or writing to it.
Open the USB & SD Speed Test. Follow any browser prompts needed to access the card or reader.
Run a read and write test with the card reader connected through the hub. Note both results and how the test behaves.
Disconnect the reader safely, then connect it directly to the computer if you have a suitable port. Test the same card again.
For a useful comparison, keep the computer, card, reader, and test conditions the same. If results are inconsistent, repeat each connection once after other transfers have stopped.

Use a port that you know works, and do not compare results taken while a large file is copying with results taken while the computer is idle. Read speed and write speed can differ substantially. For more context on one part of the setup, see why card reader speed affects SD card test results.

What the results mean

Direct connection is faster than the hub

The hub, its cable, or the way the hub shares its connection is likely limiting the reader. This is especially likely if other devices are also connected and moving data. Try the reader directly for large transfers, or test it on a different hub port with other storage devices disconnected.

Both connections are similarly slow

The hub is less likely to be the only cause. The card itself, the reader, its cable, or the computer's port may be limiting speed. A card can also write more slowly than it reads. Compare the read and write results separately instead of treating one number as the card's overall speed.

Read speed is good, but write speed is much lower

This can be normal for a card whose write performance is below its read performance. It can also happen when the card is nearly full or when a large write slows after an initial fast burst. The speed test measures performance, but it does not confirm the card's advertised capacity or prove that every stored file is safe.

Results change sharply between runs

Background transfers, other devices using the hub, a loose connection, or a card reader that heats up can affect a run. Let transfers finish, check that the reader is firmly connected, and compare again. A single short test is a clue, not a guaranteed speed for every file copy.

How to fix the slowdown

Try a different hub port. A port can be damaged or have a poor connection. Unplug and reconnect the reader firmly, then test another port on the same hub.
Disconnect other devices from the hub. Storage devices, webcams, and other active accessories may share the hub's connection to the computer. Test with only the card reader attached.
Connect the reader directly. If the direct test is consistently faster, use the computer's port for card transfers or use a hub with a suitable data connection. A hub's connector shape alone does not tell you its data speed.
Check the hub's cable and power. If the hub has a removable cable, reconnect it or try a compatible replacement. For a powered hub, check that its power adapter is attached and working.
Test another reader or card. Keep one part of the setup unchanged while you swap the other. If another card is fast in the same reader, the first card may be the limit. If both cards are slow in that reader, suspect the reader, cable, hub, or port.
Check whether the slowdown follows sleep or battery use. Test once while the laptop is plugged in and again after waking it from sleep. On Windows 11, check Settings › System › Power & battery. On macOS, check System Settings › Battery. A difference points to power behavior, but these settings do not identify a faulty card or hub by themselves.

When the card, reader, or hub may be faulty

If the card disconnects, becomes read-only, reports errors, or produces very different results across devices, stop using it for important files until you have a separate backup. Do not keep repeating write tests on a card that is already showing errors.

Test the card in another reader and computer. If it remains unusually slow or unreliable, replace it rather than trusting it with your only copy of photos or other data. If several cards slow down only through one hub, replace or repair the hub or its cable. A browser speed test cannot inspect the card's internal condition or diagnose electrical faults inside a hub.

Why a hub can change card speed

A hub connects several devices through one link to the computer. That link has a finite data rate, and active devices can share it. The reader and card also have their own speed limits, so a fast-rated hub cannot make a slower card read or write faster.

Use the same card and reader for both tests to isolate the connection. If you change several parts at once, a faster result tells you something improved, but not which part made the difference.