2560x1080 resolution becoming 1920x1080 when third screen connected

[chehsim]

Hi all,
I have a Dell work laptop from the company.
When WFH, I connect it to a docking station (via a USB) where other stuff are connected to.
I have a 34" LG ultrawide screen monitor and a 21" wide screen monitor connected to the docking station.
Problem is, when both screens are connected, both external screens display 1920x1080 only.
When I disconnect the 21" monitor, the 34" ultrawide screen will display 2560x1080.
anyone knows what is lacking to get 2560x1080 on the 34" monitor and 1920x1080 on the 21" monitor when both are connected at the same time please?
Thanks!

 

[chehsim]

O, the docking station is a Shintaro Universal Blazer Dock Station

 

[yusoffb01]

bandwidth limit. wont work with triple monitors. try disable laptop display?

 

[watzup_ken]

bandwidth limit. wont work with triple monitors. try disable laptop display?

I think it is bandwidth limited, but mostly because of the USB limit.

 

[chehsim]

Thanks @yusoffb01!
what bandwidth are you referring to?
so there's no way to get three screens? I used to have 2x 19" monitors so was able to work with three screens.

 

[chehsim]

I think it is bandwidth limited, but mostly because of the USB limit.

so it's the USB cable to the dock that is limiting the display?

 

[watzup_ken]

so it's the USB cable to the dock that is limiting the display?

Do you know if the laptop is using USB 3.0, 3.1 or 3.2? It could be the USB port on the laptop or the dock.

 

[chehsim]

Do you know if the laptop is using USB 3.0, 3.1 or 3.2? It could be the USB port on the laptop or the dock.

sorry, how to tell ah?
i only have two USB ports, under Device Mgr>Universal Serial Bus controllers there are many stuff, two of which are USB Root Hub (USB 3.0). Is that it?

 

[watzup_ken]

sorry, how to tell ah?
i only have two USB ports, under Device Mgr>Universal Serial Bus controllers there are many stuff, two of which are USB Root Hub (USB 3.0). Is that it?

I think that helps. So I think the bottleneck is the USB 3.0 here.

Max Video Resolution Supported for USB 3.0: 4096×2160p24 16bit pixel

Source: https://www.mouser.com/applications/broadcast-usb-video/

So if you try to drive 2 displays through a single USB 3.0 port, I think the max it can do is 1080p, and I suspect at a low refresh rate too, i.e. 24 to 30Hz.