Speed Simulator is a nice free tool that makes it possible to see how a website behaves under certain speed limitations. This is for instance useful if you want to see how a user with a 56K modem experiences your site and especially the loading time of it. Only the download speed can be reduced to simulate slower connections.
All you need to do is run the Speed Simulator, select a speed that you want to simulate and change the proxy in your browser to localhost and port 8080. In Firefox you do that in Tools > Options > Advanced > Network and the button Settings. Just hit start in Speed Simulator afterwards and use the browser to navigate to your website. You might be surprised about the time that some users have to wait before they can see it at all.
The difference to websites that do check the loading time of your site simulating various speeds is that you are experiencing the speeds by yourself. 20 seconds does not seem much but if you experience this by yourself you might feel that it is to much.
Update: The program is still available but it seems the website has been filled with ads on top. It is not clear if those have been injected or not, but I'd definitely recommend you check the download of the program at a service like Virustotal first to make sure it is clean.
You can alternatively use the excellent NetBalancer for that task. The free version lets you set five rules in the program which you can use to limit the bandwidth of select processes. It is easier to use than Speed Simulator as you do not have to modify proxy settings to limit the speed of applications on your system. This means in turn that you can also limit other programs that use a network or Internet connection which you cannot do with Speed Simulator as the bandwidth throttling depends solely on a program's proxy support.
Then again, Speed Simulator does not have the same process restriction as the free version of NetBalancer.
If you want to experience how slow a website or application loads in your browser if you throttle the speed of the Internet connection to a fixed value, then you may find Internet Speed Simulator useful for that task. If you need more control or want to throttle programs that do not support proxies, NetBalancer is the better choice.
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