This “faster” router setting can make everyone’s Wi-Fi worse

You can’t blame me for not questioning my router’s 2.4GHz band set to 40MHz. Who wouldn’t choose a wider channel that promises more throughput? However, I didn’t know up front that the extra width could take up more of the 2.4GHz band, potentially interfering with nearby networks.

It’s mostly going to be just fine, but that setting deserves more attention if smart plugs keep going offline or you encounter unexplained Wi-Fi stutters.

40MHz buys a higher ceiling

On paper, it claims nearly half of the 2.4GHz band

Channel width is the radio bandwidth a router uses to send data. When you set this to 40MHz, your router will combine two 20MHz channels, and you’ve theoretically doubled the link rate. For context, this theoretically jumps a single-stream 802.11n connection from 72Mbps to 150Mbps.

Theoretical maximum link rates (ceilings) differ from real-world download speeds. Your signal, device, and internet plan all affect speed, and most 2.4GHz gear doesn’t come close to using the extra width. Even though they send tiny bursts of data, your smart plugs and sensors still occupy this band.

The commonly used 2.4GHz band spans 83.5MHz, from 2400 to 2483.5MHz, although the channels available to a router depend on its regulatory region. So, a 20MHz channel uses only about a quarter of what the 2.4GHz Wi-Fi band offers, and a 40MHz channel uses about half.

The familiar 1/6/11 plan uses three 20MHz channels spaced far enough apart to avoid overlapping each other in the conventional setup. This way, nearby Wi-Fi networks operate on separate portions of the band.

On the other hand, a 40MHz channel doesn’t fit into any of those portions without overlapping the spectrum used by other networks. Hence, higher theoretical speeds may leave less room for other networks.

Your router isn’t isolated

A wide channel can’t tuck itself between the neighbors

Two Wi-Fi networks that share a channel essentially detect each other’s transmissions and take turns using the airwaves. With partially overlapping channels, a device may be unable to decode the other network’s transmission cleanly. When those transmissions collide, interference can increase errors and retransmissions.

1/6/11 exists to solve this issue by spacing channels to avoid overlap, so neighboring networks operate on nonoverlapping channels, improving coexistence. This gets harder with a 40 MHz channel taking up more of the band, and everyone’s Wi-Fi may get worse.

My router was set to channel 1 with a 40MHz width, bonding upward to include channel 5. A scan showed a neighboring network on channel 5 with an 80% signal, plus another on channel 10 at 29%. The first was a strong nearby signal, although the scan alone couldn’t tell me how much interference it caused.

To be fair, common networking advice recommends against my kind of 40MHz setup on the 2.4GHz band. Apple recommends 20MHz for the 2.4GHz band, and Intel also advises against 40MHz. I get the appeal: 40MHz sounds like a free upgrade, which is why I chose it without considering what it meant for every other network.

Some routers automatically switch to 20MHz whenneeded to coexist with other networks. In my setup, Windows recorded a 104Mbps receive rate and 72.2Mbps transmit rate, but these figures alone couldn’t tell me how often my router had fallen back to 20MHz.

Dial it back to 20MHz

A one-setting experiment, judged on reliability

The exact steps depend on your router, but the setting is usually called Channel Width or Channel Bandwidth. It should be similar to my TP-Link router:

1. Open your router’s admin page.

2. Select Wireless 2.4GHz.

3. Click the Channel Width option and select 20MHz, then Save.

The 5GHz band has more room to spread out, so you don’t have to touch it. If your Channel Width was already set to 20Mhz, you don’t need to change anything, and the stutter you are experiencing is likely caused by something else.

A good check; not a miracle switch

After making the change, test under similar conditions as before and monitor for dropouts or buffering; this gives a better reliability check than a single speed test. It’s possible for peak link rate to fall on paper despite improved stability.

If you are on a Windows computer, running the command netsh wlan show interfaces reveals your channel, radio type, and link rates. These may suffice to see what the connection is actually doing.

However, this configuration isn’t going to act like a miracle switch. If you already have weak coverage or just a slow internet plan, having a narrower channel wouldn’t do much. On 5GHz, I use wider channels, but on 2.4GHz, you get barely enough room for three lanes.