Rearview radars are pitched as an increased-safety aid that works by combining a powerful rear light with technology that senses oncoming vehicles.
I know plenty of people suggest just fitting a mirror to your bar, or your helmet. But honestly? They look somewhat geeky and they never work as well as I’d hope.
Most rearview radars use the same technology. They throw out radio waves to reflect off vehicles and bounce back to the unit.
The device then calculates the distance and speed of the approaching vehicle, which tells your bike computer, phone or smartwatch whether a vehicle is approaching. At least that’s the theory, as I learnt in a recent group test.
Wildly different results
In my testing, I found that even though radars all use the same technology, even down to the same chip boards, the results can be wildly different.
That’s down to how the programming interprets the data, and the quality of the data itself. The performance is also affected by the radar's field of view – too narrow and they miss cars entering from side roads or sitting in the next lane across.
Potentially, the tech allows for detection up to around 200 metres, but that varies from unit to unit. The 24GHZ range should allow for detection of up to eight vehicles, too.
Positive signals
Even the weakest radars in my test had their positives. They all detected vehicles when they were far away, but some suffered from false negatives where a vehicle moving at the same speed as me disappeared from detection and my bike computer screen.
Some even gave false positives, where a vehicle appeared on the screen when nothing was behind.
What the radars have going for them as a bonus is they are all housed in very good bike lights, and smart lights at that. They have built-in gyroscopes that tell the rear light to brighten as you slow, effectively equipping you with a brake light.
Plenty will dull the power when nothing is behind, and all have multiple modes.
Some of the more affordable options don’t cost much more than a premium rear light, so I’d go so far as to consider the radar functionality a bonus.
Safety, but not instead of road sense
Providing an early warning of an approaching vehicle on narrow rural roads with lots of turns is where I’ve found radars to be the most helpful.
When I’m out in the countryside, I’m usually riding quicker and am more concentrated on my performance. That means, admittedly, I might not be as focused on traffic as I should be.
Hearing a radar’s warning and seeing the screen alert is exactly what I need to remind me to pay attention.
In urban and suburban settings, I’m more aware of traffic and I’m usually riding a bike that gives me a better view. There's also the added complexity of more junctions, intersections and merging lanes, which focuses my attention.
However, radars still make me check over my shoulder, even if they are more of a copilot on city streets.
The future is bright
There was one stand-out unit from the test – Garmin’s Varia RearVue 820, which costs £259.99 / $299.99 / €299.99.
The new proprietary Bluetooth protocol is much smarter, far more accurate and less prone to any false detections. It is incredibly impressive, but you will need a newer Garmin to make use of it.
But the Varia RearVue 820 still has the older ANT+ protocol too, so the radar is compatible with non-Garmin devices and older Garmin Edge computers.
All in all, I would say yes get yourself a rear radar if you’re looking at purchasing new bike lights. Their lights are as good as any smart unit – and you get the added safety benefits. Just don’t use them as an excuse to not pay attention on busy road networks.
Keep your eyes on BikeRadar to read my full reviews in the coming weeks.
