Ping to what? What are you pinging to? Game server? Eachother's PCs?
Speed, and latency are two different things altogether. Yes, generally speed will be higher on wired simply because wireless connections, even with the best signal cant best a 100Mbps wired connection. But latency is communication time, out and back to another node, computer, router, server etc, you can ping a server on a LAN with a wireless connection that has terrible reception and is running at 2Mbps and get a latency of 5ms. Then ping the same server, on the same LAN with a workstation on a wired gigabit connection, and still get 5ms ping even though the connection is 500 times faster.
Exceptions to this can be a dial up connection connecting to a game server vs. a broadband, but those speeds are so different, and we are talking in terms of the internet, not a LAN like we are here, besides, really, the difference isnt really THAT much different. I used to play QUake II back in 1997 on a 28.8 modem and pinged 180ms to my favorite server. The same server pinged 120 when i got cable a year later. Negligble results.
So what is it you're pinging?