Trek CarBack Radar Tail Light: Garmin Varia Alternative, Reviewed

The Trek CarBack launched in late 2025 as the first credible challenger to Garmin's Varia RTL515 in the radar tail light category. After 3,000 km of testing alongside a Varia RTL515, here's how they compare.

Detection performance

Both the CarBack and Varia detect approaching vehicles up to 150 m behind the rider. In real-world testing on rural roads, both detected consistently at 110-130 m. False-positive rates are similar: both occasionally trigger on roadside signs or parked cars in cross-traffic.

The CarBack's detection algorithm is slightly more aggressive in identifying multiple threats simultaneously. In dense traffic, the CarBack's display showed up to 4 vehicles, while the Varia showed up to 3.

Battery life

CarBack: 20 hours solid, 35 hours peloton mode. Varia RTL515: 16 hours solid, 24 hours peloton mode. The CarBack wins by 25-50% on battery, which matters for multi-day events or forgetful chargers.

Brightness

CarBack: 150 lumens solid, 350 lumens day flash. Varia RTL515: 20 lumens solid, 65 lumens day flash. The CarBack is significantly brighter, making it more visible in daylight traffic. This is a meaningful safety upgrade for urban riders.

App integration

The CarBack works with any ANT+ radar display (Garmin Edge, Wahoo, Hammerhead). The Bluetooth connection is for Trek/Bontrager's own app, which is less polished than Garmin's Varia app. For most users, the head-unit display is what matters, and both work equivalently there.

The verdict

The Trek CarBack is a real improvement over the Varia RTL515: brighter, longer battery, slightly better detection. At $229 vs. $199 for the Varia, the CarBack is $30 more. For new buyers, the CarBack is the better choice. For existing Varia owners, the upgrade isn't compelling unless you specifically need the extra brightness or battery.