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RT-AC86U and RT-AX88U - firmware for best performance and range

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Hunny Puppy

Occasional Visitor
First up, I want to thank this awesome community and also @RMerlin for the amazing work he's done with Asus Merlin (I've been a follower since the RT-N16U days ;)

I had a RT-AC86u and it's a TOTAL beast in it's class because it literally beat every other router in it's price (including a Unifi AC LR that I own), it's range of coverage was outstanding and it's speed was brilliant for the range (it's not the faster overall but it is fastest given the range the router can cover). I needed to upgrade to get more speed (and hopefully more range) so I decided to get the RT-AX88U (because the RT-AX86U wasn't available). I've been playing with them both and I wanted to share my feedback after days of testing the stock and the Merlin firmware on these routers.

First up, I want to point out a few fundamental differences I found between the two routers in my testing. Again I'm testing for range and for the best speed I can get from the range (one router to cover a 5000sq ft house).

The RT-AC86U consistently gave me 6-9dB higher signal in both the 2.4 and 5Ghz bands. The 5Ghz band on the RT-AX88U was at a minimum 6db lower than the RT-AC86U at ANY distance (from 5ft to 300ft). I also noticed that the RT-AX88U 5Ghz signal constantly fluctuated by about 4-6dB and was NEVER steady, the RT-AX86U on the other hand was a ROCK steady the the signal levels never fluctuated. For testing purposes, both routers were configured identically and setup up right next to each other using the same bands and settings.
I also found that while the RT-AC86U had a longer range than the RT-AX88U, for the given signal, the RT-AX88U delivered higher speed. So while the signal levels for the AC86U were higher, the throughput at the same distance (with a lower signal level) was higher for the AX88U. I'm chalking this up to the better AX standard (modulation etc). So inshort, it was more difficult to catch the AX88u signal but when caught it performed better.

I noticed a few things which helped boost the signal range and the speed throughput.

1. Put the routers USB ports into USB 2.0 configuration (USB 3.0 interferes with the 2.4Ghz band by creating a lot of radio "noise", this is a known issue with 3.0 ports which has caused me a lot of grief even in laptops).
2. For the 5Ghz band I decided to use the 149 and higher channels. Conventional wisdom tells us that a lower band frequency will travel further, so channel 36 which is around 5.2Ghz should travel further than channel 149 which is around 5.8 Ghz. However one tends to over look the fact that different channels actually have different regulatory power transmission limits. Channel 36 has a limit of about 200mw where as Channel 149 has a power transmission limit of 4000mw, so where as the range is lower, because the power transmission was significantly higher for channel 149 I got a signal much further out and much faster speeds using Channel 149 vs 36 (see this for details https://w.wol.ph/2015/08/28/maximum-wifi-transmission-power-country/). On the flip side, note that devices will also need to use a much higher power to communicate back with the router on channel 149 which may affect battery life. So if battery life is more important than range then stick to a lower channel. Also note that Channel 149 has a maximum width of 80Mhz where as channel 36 can go upto 160Mhz which will make a different in the maximum speed you can get from your 802.11ax devices. I'm not sure if the RT-AX88U supports a split 80+80 channel strategy or if it only supports a contiguous 160Mhz channels. From my reading the 80+80 never works in practice so if you need 160Mhz then stick to channel 36.

Finally coming to the firmware, after extensive testing across multiple different versions of firmwares including the stock and the merlin firmwares, I finally arrived these firmwares which gave me the best range, stable signal levels and the best speed for that range.

RT-AC86U - (stock) - https://dlcdnets.asus.com/pub/ASUS/wireless/RT-AC86U/FW_RT_AC86U_300438646092.zip
RT-AX88U - (stock) - https://dlcdnets.asus.com/pub/ASUS/wireless/RT-AX88U/FW_RT_AX88U_300438646065.zip

Unfortunately I found that the Merlin firmware were a tad bit slower than the stock firmware (amongst the best versions), although the Merlin firmware had more features in it. If you need to go for a Merlin firmware for the RT-AX88U I found that version 386.8.0 was the best firmware which had a speed and range that was close to the stock 386.46065, the difference was a slightly slower speed and less consistent upload performance. (https://sourceforge.net/projects/asuswrt-merlin/files/RT-AX88U/Release/RT-AX88U_386.8_0.zip/download)

I did however find that any newer version of the firmware were either slower, had a signal fluctuation issues or had lower range. The new 388.xx firmware (both stock and Merlin) performed the worst, had a lowest range and had much slower speeds with less consistent/reliable connections. I don't know what's changed in the 388 vs 386 the difference is day and night.

Thank you all for reading and again this is just my experience. I do wish I had the RT-AX86U based on my experience with the RT-AC86u and from what I've read from benchmark websites and other users but if you had to settle for the RT-AX88U I hope this helps.

If you have any suggestions on how else to juice the range or speed for these routers please feel free to share

These are the Wireless settings I used for testing

Wireless - Professional
Band     5 GHz
Enable Radio    Yes
Enable wireless scheduler    No
Set AP Isolated    No
Roaming assistant    Disable
Enable IGMP Snooping    Disable
Multicast Rate(Mbps)    Auto
AMPDU RTS    Enable
RTS Threshold    2347
DTIM Interval    1
Beacon Interval    100
Enable TX Bursting    Disable
Enable WMM    Enable
Enable WMM No-Acknowledgement    Disable
Enable WMM APSD    Enable
Optimize AMPDU aggregation    Enable
Modulation Scheme    Up to MCS 11 (NitroQAM/1024-QAM)
Airtime Fairness    Disable
Multi-User MIMO    Enable
802.11ax/ac Beamforming    Enable
Universal Beamforming    Enable
Tx power adjustment    Performance


Enable Smart Connect    No
Band    5 GHz
Wireless Mode    N/AC/AX mixed
WiFi Agile Multiband    Disable
Target Wake Time    Enable
Channel bandwidth    20/40/80/160 MHz Enable 160 MHz
Control Channel    161
Extension Channel    Auto
Protected Management Frames    Disable
Group Key Rotation Interval    3600
The RT-AC86U consistently gave me 6-9dB higher signal in both the 2.4 and 5Ghz bands.
for channel 149 I got a signal much further out
Unfortunately I found that the Merlin firmware were a tad bit slower than the stock firmware
I did however find that any newer version of the firmware were either slower

All of the above applies to RT-AC86U vs RT-AX86U comparison. The best Asuswrt version I found is 386_49599 and the best Asuswrt-Merlin is 386.5_2 based on GPL 386_46065. The newer versions have issues indeed, but stock Asuswrt 388 firmware still has better Wi-Fi and properly working AiMesh.
Asuswrt-Merlin is 386.5_2 based on GPL 386_46065
Yes I did see that in the change log so I expected that firmware to be faster (as that eq stock version was the fastest for me), however in practice for some reason it gave me a slower performance (not by much, maybe 10-20mbps) than the 386_8_0 which as based on a newer stock firmware. Go figure ???

The comparison above was done between the AC86u and the AX88u (wish I had the AX86u)

My testing was done using an iPhone pro 12 as the primary device to replicate real work scenarios. When using a laptop with a AX card I got much better results than the iPhone and the differences between the firmware versions were less (guessing because the laptop has a more sensitive and power antenna built in)
wish I had the AX86u

You don't need it. If AX88U doesn't perform well in your environment AX86U is going to be the same or a little worse. I had both at one point and AX88U was a little better in range. Asuswrt 386_49599 is AX86U firmware. In general don't use mobile devices for speed assessment, may not be accurate.

AX routers have advantage in shorter distances only and lose speed fast because of 1024-QAM used with AX. Radios can maintain 1024-QAM up to about -65dBm levels. AC uses 256-QAM with possible higher radio sensitivity - in some routers up to -90dBm. This explains what you see in real tests.
These are the Wireless settings I used for testing

By the way, this setting:

Optimize AMPDU aggregation    Enable

...may break time-sensitive applications like voice/video calls. It's disabled by default and better leave it disabled.

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