Wireless download slowed – upload unchanged

I recently set up a wireless connection using WPA2, and ran some speed tests. Going through the same router (WRT54G), I got these results:

(Down/Up)
Hard-wired: 5.44Mbps/4.62Mbps
Wireless: 1.84Mbps/4.59Mbps

I can’t find anything that might indicate why the download speed would be so slow on wireless, while the upload speed remains unchanged.

Any thoughts?