Garmin Varia RearVue 820 Review: Key Specs and RTL515 Comparison

The Garmin Varia RearVue 820 is the new radar taillight for cyclists who take road safety seriously. It replaces the RTL515 with a spec sheet that's hard to ignore: 175m detection range, 50% longer battery life, vehicle size identification, and an active brake light function.

That 175m detection window gives you real reaction time at road speeds. On a descent at 40km/h, you're getting roughly 15 seconds of warning before a vehicle closes in. The RTL515 already felt useful at its detection range, but this pushes it closer to genuinely reliable on faster roads and rural routes where traffic approaches quickly.

Vehicle size identification is the standout new feature. The 820 can distinguish between a car and a larger vehicle like a van or truck, which changes how you read the alert. A single car closing at moderate speed reads differently than an HGV, and knowing that in real time lets you make smarter positioning decisions rather than reacting the same way to every ping.

The brake light alert is a logical addition for group riding and urban cycling. When you slow sharply, the light pulses to warn following riders or drivers. It mirrors what you'd expect from a Garmin Edge head unit integration, and the 820 pairs cleanly with the broader Garmin ecosystem including Edge 540, 840, and 1040 series.

At £90 more than the RTL515, this is not a casual upgrade. But if you ride fast roads, do long audax events where battery life actually runs out, or commute in mixed traffic, the 820 earns its price. Solid piece of kit with real-world utility.