In a simple words, it’s all about the percentage of seeders in a swarm(seeders and leachers)
The fastest torrents will be those where downloaders (leechers) can tap into the most upload capacity. If you have a swarm (seeders and leechers) with a hundred people in total it will be faster when there are relatively more seeders. Why? Very simply it’s because seeders don’t download while their upload capacity is available for the leechers.
Many people understand these basics. A torrent with 30 seeders and 70 leechers (30% seeders) will go faster than one with 10 seeders and 90 leechers (10% seeders). However, it get confusing when you compare swarms of different sizes.
For example, a torrent with 30 seeders and 70 leechers (30% seeders) will generally be faster than one with 500 seeders and 2500 leechers (20% seeders). Why? Simply because the swarm has a smaller percentage of seeders. When picking the right torrents to download, the percentage of seeders that a swarm consists of is the most important thing to look at.
A higher percentage of seeders means that the average upload capacity available to the leechers will be higher.
So next time you go looking for a fast torrent, don’t just head straight for the download with the most seeders. Instead, find the torrent with the highest seeder to leecher ratio.
How to Pick The Fastest Torrents [TorrentFreak]