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Tweaking your MTU settings.

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Tweaking your MTU may help resolve some problems such as slow adsl speeds and problems connecting to certain sites. I have a specific page dedicated to MTU problems, and a page which gives a more in depth view on how to calculate your MTU and RWIN settings to optimise your connection and get better speeds.

This page is more of an introduction to tweaking your MTU and RWIN with some suggested settings that have worked for many. The best way to tweak your settings is to download and use Dr TCP

My speed increased by about 30kb after tweaking a 512 kbps connection (to 478/250kbps). When on 2Mb I got a speed increase of around an extra 50 kbps. The amount of speed increases can and does vary - sometimes with remarkable results.

So if you are looking for the basics of MTU tweaking and some suggested settings then read on:-

How to tweak your MTU and RWIN

Note: Dr TCP does not work with Windows Vista and you will need to manually adjust your MTU value - See Changing your MTU in Vista

MTU - RWIN Calculator

  • Download Dr TCP

  • unzip to folder and run from your desktop.

  • Select your Connection Speed from the MTU/RWin calculator on the right.

  • Choose an MTU value. 1458 works well, 1430 is a personal preference of mine. AOL users should choose 1400. (TT users should also try 1400).

  • Change the relevant settings in Dr TCP using the image as a guide.

  • Make sure you choose the correct Adapter Settings from the pull down menu *

  • Save the changes.

  • Reboot your PC.
 Connection Speed
 Select MTU

dr tcp
tweak your mtu rwin
tweak your mtu rwin tweak your mtu rwin tweak your mtu rwin tweak your mtu rwin tweak your mtu rwin tweak your mtu rwin

* Under "Adapter Settings" select the following options:-
For a usb modem select Dial up RAS
When using a router select your Ethernet Card (NIC)
For Laptops and Wireless select your Wireless adapter.

More Information

Dr TCP is provided by dslreports, who also provide a tweak tester where you can check your results.
When imputting your information into the tweak tester if on adsl you should use the following settings:

MTU test results


|| Tweaking History || Understanding MTU and RWIN || MTU Problems|| Vista MTU ||

Some more recommended settings.

Different people tend to get best results with different settings,
so it may be worth spending a bit of time to find the best for you.

512kb connections
1458 12762
BT original suggested setting.
1430 13900

Pengbo + Tams recommendations.
* probably the best settings for most 512 users.

1478 14380
Another of Tams, that works best for some.
1458 14180  
1472 14320  
1500 14600  
1Mb connections (Use 2x the rwin)
1430 27800
If you found 1430/13900 worked best for you on 512kb then this may well be the best setting for you on 1MB
1478 28760
Doubled rwin for tams 1478/14380
1458 28360
1472 28640
1478 25884
Guest_SO's recommended settings.
1458 9000
This supposedly weird setting was discovered by nickvid. It sucessfully managed to increase speeds for users who were previously having problems with 1Mb connections. This sparked a few more low rwin suggestions.
1478 8628
Another weird recommended setting
1500 8760
Best settings for one user (cjtc)
2Mb connections (Use 4x the rwin)
1430 55600
Best setting based on the 4x theory.
1458 56720
" "
1472 57280
" "
1478 57520
" "
1478 51768
Guest_Again's recommended setting for 2MB.
1458 64512
MHC's recommended setting.
8Mb connections
1478 75020
Guest_Again's recommended setting for 8MB.
1478 75060
Twitch's recommended setting
1478 78840
1430 65535
TriGGa's recommended setting.
1430 84300
1430 166800
What Im currently using and seems to work best for me on a stable 8Mb connection
1430 111200
Another setting that works pretty well for me and should work well with 4Mb speeds.


AOL Suggested Settings
1400 13600
512kb connection
1400 27200
1Mb connection
1400 54400
2Mb connection

With the advent of maxDSL higher speeds, we are now seeing various sync speeds and users may be unsure what settings to use. The following information kindly provided by Guest_Again will be useful in these circumstances.

Non standard sync speed settings.


  •   First, set your rWin [Top Receive Window] in DRTCP to 1000000, save this setting and RESTART your PC. (it's way to high but you'll see why in a minute).

  •   Next, go to and start the Tweak Tester, when it's finished, press the Results button.

  •  On the next page enter the following in the 'Final Step' window: Service - DSL, Speed - [*See Below], OS - XP, Connection - WinXPpppoe, now click Recommend...

  •  On this page you will see on the middle left hand side " Choose RWIN between 'xxxxx' and 'xxxxxx' (FAQ #586)" - choose the lowest setting and put that into the Top Receive Window in DRTCP, click Save and then restart your PC again.

  •  Now try another speed test.

    * Enter the speed that your modem / router is synced at.



RWIN = n * (MTU - 40)
where n is a whole number.

n can be 2, 4, 6, 8 or 16 (8 is the Win9x default),
although 9 is recommended by pengbo

ping -f -l [size] [url]

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