WiFi channels are not a single channel the are a group, channel width determines how much of the radio frequency band that channel uses.
2.4Ghz typically uses 20Mhz as theres only around 60Mhz usable and you don't want to overlap other networks.
5Ghz can use up to 160Mhz which is why it can go so much faster, though a lot of routers and clients only support up to 80Mhz.
The speed you get at long range will reduce as you increase the channel width, but the speed you get in closer range will increase. So it can be a good idea to test different widths to see if it performs satisfactory in all the places you use wireless.
Another thing that impacts your speed is MIMO, a lot of clients are only 1 transmit 1 receive, or 1x1, the higher the MIMO the faster your WiFi link can go at the same channel width.