Why does my internet spike when using torrents?

I set up the port correctly, removed firewall, I had no problems before on campus with Torrents.

Now I'm in Chicago using SBC Yahoo DSL and I find that every so often my internet spikes only when using torrents.

The spikes could be attributed to running into a bandwidth cap, like alpine said. As you see, it builds up to a peak, then the cap kicks in and kills it down, then it rises again and the process repeats. I've had downloads look like that myself at times.

BitTorrent is overloading your connection. Downloading from Microsoft is a connection between you and one server, downloading from BT means dozens of connections from you to other people also downloading the same file.

At your school, they undoubtedly had a much faster connection than you do at home. Also, BT is also uploading traffic back to other users. If you run a constant ping while downloading some random file, it might go up a bit but not too much, now if you upload a file to a FTP server or a website, your latency will skyrocket. This is because your downstream bandwidth is a lot higher than your upstream, so when you upload something, all your bandwidth is used up and your latency climbs.

That must explain why everybody has this same exact problem. :?