Wifi download terrible

[#1]

So I've got quite a few computers but only one of them is connected via cable, the rest are wi-fi'd.
I'm trying to download on these via steam or any other program and the speed is no where near as the cabled one. Is this the router?
my cabled pc gets 8.8mb sec
wifi gets 2.2mb

[#2]

It could be so many factors causing this, from the router, to the wifi adaptors, to the distance between the router and PC and also other wifi signals in the area could conflict with yours.
http://www.plus.net/support/broadband/wireless_broadband/ - This may help, try a few different channels on the wifi and see whether it improves.

[#3]

If you have an android phone download wifi analyzer it can show you what channels are active and see if there is a conflict