Which ones work, which ones don't – and which might be worth your money.
Cycling rear radars tested: Garmin, Trek, Wahoo and more
Suvi Loponen
8–10 minutes
Suvi Loponen
Rear radars used to be a niche accessory for safety-obsessed and tech-forward. But not anymore. Since Garmin bought South African startup iKubu and released the original Varia radar, now nearly a decade ago, the tech has matured to a point where it's a staple of many riders' everyday setup.
The premise of radars is simple: a second set of eyes to alert you of traffic approaching from behind. The added bonus is that the same device doubles as a rear light. But while the concept of a rear radar seems simple, not every radar is created equal. The market has instead grown with products that are half-baked at best, as we'll cover. But there are some promising newcomers, too.
This group test reviews six rear radars that are currently available: Garmin Varia RTL515 , Bryton Gardia R300L, Trek CarBack, Magicshine Seemee 300, Giant Recon+ TL300 R, and the newly released Wahoo Trackr radar. Yes, there are lots more radars out there, but as you'll see, it's better to pick the right one once rather than try the newest thing twice. Or thrice.
Why use a rear radar?
The question “What’s the point of a rear radar?” and "Oh, did it detect that?" were both questions that came up a lot during testing, often mid-ride, from someone riding next to me, listening to the endless beeping of my cycling computer. And that's a fair question. First of all, rear radars are not cheap, and second, they won't suit all environments. Third, you still need to double-check for cars.
All radars are susceptible to both false positive and false negative alerts. A false positive is when a radar detects a vehicle when there isn't one: annoying, but usually not more than that. A false negative, or failure to detect a vehicle that is there, is far more worrisome and, unfortunately, at least a sometime occurrence with two of the radars we tested. In contrast to those concerning performances, the primary instance for a false negative is one all radars struggle with: vehicles traveling at your speed. All of the radars in this test sometimes failed to track – or initially detected but then lost track of – the vehicle behind when it matched my riding speed, giving me a false-negative "all clear" signal. The key difference is that some of them did this more than others.
So what do they detect, then? Most radars perform best on straight, flat, open roads with little road furniture, because the radar can't see around corners or through solid objects. When they do detect a vehicle, they'll alert you it's coming and how many; if it's coming fast, they'll tell you that, too.
In the months I’ve been testing the six units, the weather conditions have made it pretty hard to hear the approaching vehicles from the midst of a crunching drivetrain, howling wind, and battering rain. In these conditions, I found myself appreciating the audible "beep" from my head unit more than expected. My colleague Joe Lindsey, who has cochlear implants, relies on this even more, and really highlights that a radar can be a valuable helper for those with hearing loss.
But as Lindsey, who rides with a Trek CarBack, put it: "It hasn’t changed how I ride – where I am in the lane or shoulder, or my behaviors and attitude. It is a valuable addition to the “Swiss cheese” security approach I use for riding, but it is not and never will be a replacement for those other habits. And I think no matter what radar I use, that will always be the case."
Another place for radars is on longer, winding descents, where they can really help in getting a heads up of a car overtaking. While I’d still ride around corners taking more space on the road, the radar can alert me to move to the side when the road straightens to give space to the car to pass.
And lastly, on group rides, a rear radar might not have the best detection field through other riders, but most of the time, it will still alert you about cars when there are one or two riders behind. This is even more useful if perhaps your riding companions don't notice the car approaching.
In an urban setting, a rear radar is almost more of a nuisance than a help. The constant flow of traffic will only cause your head unit to beep constantly and rather than make you feel safer, it can be more of a distraction.
Once you get used to riding with a radar, it's hard to go back. But there's a caveat to this: that only applies to radars that work.
Where they shine and fail
Before getting to the nitty gritty of which radars worked and which didn't, it's worth talking a bit about how I tested these things. In short, testing these is pretty frustrating. Just as you have a good grasp of the performance, there's a firmware update, and suddenly the radar behaves in a different way.
To keep things relatively comparable, I rode with each radar (sometimes two, each connected to a separate cycling computer) as part of my normal riding setup, as well as on a specific test loop, that included fast two-lane road, quiet residential streets with parked cars, open B-roads, as well as shared pedestrianised paths with lots of trees and clutter. I live in the suburbs of Scotland's second-largest city, so usually my rides included plenty of traffic, whether I wanted it or not.
Some of the head units I used for testing, all showing the same car approaching.
The established tech gurus Ray Maker (DC Rainmaker) and Shane Miller (GPLama) are the benchmark in testing any tech of this sort, and as such, I adopted similar approaches. But here, it's worth noting that there is a lot of variability in any testing done on open roads. The traffic conditions are never the same on two test rides, and neither are the speeds of the cars, or the other obstacles on the road.
When I spoke with Miller about my testing frustrations and radars in general, he strongly emphasised that the more people test and report on these radars, the better. We all ride in slightly different conditions, and while some countries might be blessed with a lot of segregated cycle lanes, keeping you away from vehicles, others force you into the midst of the traffic on shared, narrow roads. In the UK, the latter is true, and high hedges along the narrow country roads are common, whereas in the US and Australia, roads are much more open and often include wide hard shoulders that give you more space.
Two scenarios where radars struggle: obstructed sight lines and busy urban environments. Photos K Mitch Hodge (left) and Eddie Junior (right), courtesy Unsplash
While a dead straight, wide road with no furniture, trees, or hedges offers the radars a clear path to bounce off only the vehicles, the bends and bumps trick them. Depending on the detection radius of the radar, most of them temporarily lose a car when you go around a bend, and similarly when you dip to the descent of a blind summit. In these instances, you're likely to be alerted that the road is clear, and after a brief moment, that it's not. This is something you get used to, and it's affected by the detection radius (also called beam width) of the radars, which varies from 40 degrees on the Garmin Varia RTL 515 to 35 degrees for most others.
When assessing the accuracy of a radar, we usually refer to false negatives and positives. Losing the vehicle temporarily could be classed as "false negative," but it's not really the case. Rather, true false negatives are situations in which the radar says there is nothing behind you when, in fact, there is a little boy racer BMW about to speed past an inch away from your elbow.
False positives, which the Giant radar was prone to in the beginning, are also annoying, but they are much less of a safety issue, as if you think there is something coming, you're wary of it. But constant false alarms, whether negative or positive, erode your confidence in the device.
Before getting into my findings, let's start with an overview of the features that all these radars I spent months riding with offer.
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