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I'm experiencing an invisible upload speed cap


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I started a thread about this subject some time ago, but due to being busy I wasn't able to reply as fast as I would like. And since I am not allowed to double post, I cannot bump it so I can get an answer.

Therefore I'm reposting it here again, with a link to the original (hope that is okay).

Link to original thread

I hope someone can help me with this because it is severely limiting my ability to upload when I'm not here.

The general problem I'm having is this:

If I set my upload speed to unlimited, I can upload at whatever speed my connection allows (180-190 kb/sec). If I set a speed limit, the upload caps at ~100kb/sec regardless of the speed limit I set.

Example 1:

I set my upload cap to 150 kb/sec.

After a while the total upload speed of the 5 torrents I am seeding is steady at 90-100 kb/sec.

I change the upload cap to unlimited.

After a short while the upload speed rises to and stays at 190 kb/sec.

I set the cap to 150 kb/sec again.

The upload speed drops to 90-100kb/sec and stays there.

Example 2:

With a single seeding torrent at 20 something connected peers, I can upload at around 190-200 kb/sec with no upload limit set in utorrent.

With the same torrent and the same peers in the same utorrent session, if I set an upload limit in utorrent of 150 kb/sec (40-50 kb/sec less than the speed at which I'm currently uploading), the actual upload speed will drop to 90-100 kb/sec and stay there.

Example 3:

I set the upload speed to unlimited and the upload speed rises to 190 kb/sec. I then set the limit to 200 kb/sec and the speed drops to 100 kb/sec.


I'm using whatever standard settings utorrent installed with (I set the speed to xxx/2 mbit).

The quality, number of peers and speed of them is very high/very good (as in there are lots of peers and I know they can download more than I can upload).

Standard wired adsl with no software firewall (Avira antivirus with nothing but antivirus enabled).

The torrents I'm uploading at the moment have 50+ leeching peers each. I'm connected to about 20-30 on each.

I know they (the peers I'm connected to at the moment) can handle at least the 200 kb/sec upload that I can send out (as in, I can send to them at 200kb/sec if I just set the limit to unlimited).

Upload slots are set to 25 (with the option to increase when speed is <90% enabled).

Global maximum number of connections is 700. Maximum per torrent is 60.

Atm I'm uploading to about 70 peers, the number changes, but the invisible cap behaviour is there regardless of the number of peers.

The peer flags don't appear to change, nor does the number of connected peers, when I change the upload speed to unlimited.

As far as I can tell (I'm not a log expert though smile ) there is nothing in the log that indicates what is wrong.

No, I haven't used the TCP optimizer because I generally don't trust those "optimizer" applications as something machine-specific like optimization cannot and should not be generalized. (I haven't tried this particular optimizer, it might work)

I'm using utorrent 1.8.2

Edit: If I set the upload speed cap to something really high the upload speed rises. If I set it to 250-300 kb/sec (100 more than my connection can handle) the speed rises to around 150 kb/sec. If I set the cap even higher, the speed rises to the maximum of what my connection can handle.

It is almost as if utorrent is "saving" some bandwidth for something. But why?

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