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The Knog Big Cobber Rear light uses its swooping wraparound design and 270-lumen output to fire almost blindingly obvious signs of life into overtaking traffic (assuming there's any intelligent life there to receive them). You can check it's on without performing contortions, eight useful modes give between two and 100 hours of burn-time, and it's simple to use. The low battery warning is inadequate, however, and it takes ages to charge.
The Big Cobber is a simple design that works really well in almost every way. A long press of the single button switches it on or off, short presses cycle the modes, and a red ring indicates low power/still charging. Once it's 100 per cent charged, the ring goes green.
On the road, however, that ring only lights red with less than 15 minutes to go – I can't narrow it down further as it tended to silently die between checks without me ever even seeing it. There's no other way of checking battery status, and the 5.5hr charging time (on a mains adaptor – a computer is slower still) means there's no quick fix.
This means it's not good for long or multiple rides unless you're careful with your mode selection; the five main flashing options can be mistaken for each other, and their run-times vary between 6.5hrs (Flash) and just 2hrs (Side Flash). Yes, there's a 100hr Eco Flash, but it's more off than on and only gives 15 lumens.
That said, Knog lists run-times for each mode and they're very accurate, so as long as you're careful it's an excellent light. Knog also calls it a commuter light, so perhaps it's not fair to judge it for longer rides, but a) it's potentially excellent for them and b) the mystery battery status and nearly workday-long charging time pose the same problems for commutes.
The whole thing is re-programmable via Knog's Modemaker app, if you really want to fine-tune the flickering, but quite how many rear-light enthusiasts are looking to go that far is up for debate.
The simple 6g o-ring bracket is stickily soft-backed and more than enough to support the 56g unit, and slides securely into grooves to stick with both friction and a magnet. You even get a second bracket in the box shaped to fit aero posts.
Removing the bracket reveals the male USB connector, and though it's well covered it's apparently designed to cope with water anyway, which is sensible. I had no issues with it degrading or even getting particularly dirty during the test.
The light unit is neatly made, well sealed and solid enough, though it stops short of feeling particularly tough – the plastic is stiff and inflexible, and you probably wouldn't want to drop it on concrete too regularly. The bracket is a more bendy material and feels more resilient.
The 330-degree beam spread is excellent, especially for city riding or around junctions, and I particularly like that the forward-facing edges light up. It means you can check it's on with just a quick glance towards your feet – it's bright enough to show in your peripheral vision even in the day – rather than throwing crazy shapes across the road trying to peer under your own bum.
There are similarly bright lights available for less, such as the £45 NiteRider Omega 300, but dodgy waterproofing restricts that to dry rides only. Blackburn's DayBlazer 125 is less powerful but still bright enough for day or night, and also £45, while Lezyne's excellent if slightly clunky Strip Drive Pro 300 is £50 and shoves out 300 lumens for five hours.
None have quite the wraparound loveliness of the Big Cobber Rear, but it's hard to argue with lower prices, faster charging and – certainly in the Lezyne's case – a more reassuringly sturdy build.
Note that Knog's own medium-sized Cobber is £60 and fundamentally the same, just smaller and, at 170 lumens, less powerful.
Overall, the Knog Big Cobber is a very bright, very eye-catching rear light that's easy and pleasurable to use, but slightly let down by the lack of a meaningful status indicator, long charging times and a high price. Under careful and considered use it is, however, excellent.
Really bright and safe rear light, but expensive and some battery niggles
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road.cc test report
Make and model: Knog Cobber Big Rear Light
Size tested: Max lumens: 270
Tell us what the light is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
Knog says: "Big Cobber produces an incredible 330 degrees of light, so you'll be clearly seen from all angles. In an increasingly busy world, this bike light is brilliantly effective at attracting attention and helping keep you safe on the road. Packing 270 lumens this Big Cobber is seriously bright."
Tell us some more about the technical aspects of the light?
Knog lists these things:
LIGHT MODES : Max, Mid, Steady Pulse, Flash, Rolling Flash, Side Flash, Disco Flash, Eco Flash come pre-programmed.
LEDs : Efficient Chip on Board (COB) LEDs designed to provide maximum brightness level for up to 90% of the battery burn time for each mode.
INTEGRATED USB PLUG : No charging cable required, plugs directly into USB ports & is designed to be exposed to the elements
100% WATERPROOF : The Cobber is 100% waterproof against all elements
CHARGE TIME : 5.5 hours (LED will turn off when fully charged)
BATTERY : USB Rechargeable Lithium Polymer
BIKE ATTACHMENT : Tool-less removable silicone straps for bars/seat posts 22 - 32mm+ diameter with magnetic mount. Aero Mount also included.
ACCESSORIES INCLUDED : Standard Mount, Aero Mount, 3x interchangeable straps for bars/seat posts 22-27mm / 28-32mm+, and USB extension.
Neat and tidy, though rigid plastic might break instead of bend under impact.
Very simple to charge, attach and adjust.
Simple O-ring is perfectly secure.
Knog's burn-times seem accurate, which is useful. Very long charging cycle is not.
Very bright with excellent side visibility.
Perfectly good for normal use, though hardly burly.
More expensive than lights that can outperform it.
Tell us how the light performed overall when used for its designed purpose
Tell us what you particularly liked about the light
Very bright, lightweight and easy to check it's on while riding.
Tell us what you particularly disliked about the light
Dies without adequate warning, takes ages to charge.
How does the price compare to that of similar products in the market, including ones recently tested on road.cc?
It's £20+ more than some very strong competition.
Did you enjoy using the light? Yes
Would you consider buying the light? In a sale, yes.
Would you recommend the light to a friend? Yes – with caveats.
Use this box to explain your overall score
This rear light is bright, visible from almost all angles and easy to use – just what you want. If it was £20 cheaper, had a useful status indicator and charged in a couple of hours it'd be a 9. If it was palpably rugged as well, it may even be a 10. As it is it's good, but certainly not great, and a 7.
About the tester
I usually ride: Vitus Zenium SL VR Disc My best bike is:
I've been riding for: 10-20 years I ride: A few times a week I would class myself as: Experienced
I regularly do the following types of riding: general fitness riding, mountain biking