Givi GRT729 motorcycle tank bag

The problem every tank bag has: a fuel tank is not flat. It is curved and slippery, especially after a wash or in morning dew. Straps stop the bag flying off, but they do not stop it rotating and creeping to one side over a few dozen kilometres of rough road.

How this model handles it: the maker applies a non-slip PVC layer to the base, stated explicitly as being there to increase stability. That layer grips the tank by friction rather than magnetism, so it works on a steel tank and a plastic-covered one alike.

The practical consequence: this model uses no magnets, and does not need them. On a bike with a plastic tank cover, it is one of the few tank bags that sidesteps the whole question of whether magnets will grip.

Benefit: elastic holds by stretch, so its tension varies between fittings and as the strap ages. A cam buckle clamps the webbing between toothed jaws, so the tension you set is the tension it keeps, with no creep over time.

Evidence: the GRT729 uses four cam buckle straps, which the maker states are there for a secure hold with quick attachment and release. Four anchor points across four corners leave the bag nowhere free to rotate.

Tightening it properly: pull all four evenly rather than cinching the front pair and leaving the rear pair loose, which lets the bag nose forward under braking. Once done, rock it sideways by hand, and tighten further if it still moves.

Benefit: within tank bags there are three ways to carry a phone: a clear window sewn into the lid, a MOLLE panel needing a holder bought separately, or a detachable pouch like this one.

What the detachable kind gives you: the GRT729 pouch is waterproof, attaches on top of the lid and comes off. Stopping for coffee or heading to your room, you pull the whole pouch off and take it, instead of prising the phone out of a sealed slot and pushing it back later. It is also the only one of the three where the phone stays protected once it leaves the bike.

Said plainly: the maker describes this pouch as waterproof without attaching any technical rating to it. That means it handles rain and spray in normal riding, while submersion is not something to test.

The limits first: three litres, rated to two kilos. It is the smallest tank bag the shop carries, and it was designed small rather than cut down.

Three litres takes: a wallet, documents, keys, a power bank and a pair of thin gloves. The phone lives in the detachable pouch on the lid. Three elastic straps inside stop those items sliding into one corner every time the bike jumps, a detail you only appreciate on bad roads.

Why small is the point: on an adventure bike, most luggage rides in cases or a bag behind the seat. The tank bag exists only as the place you can reach at a stop. Keeping it small and low leaves your view of the dash clear and keeps it away from your knees when you stand on the pegs.

Pick the GRT729 if you ride an adventure bike on dirt, want a small bag that stays put on the tank, and want to pull the phone off and take it every time you stop.

If you mostly ride town and tarmac, the six-litre GIVI EA138B at 864,000d is enough: double the capacity, a phone window already in the lid and a rain cover in the box. For a genuinely large space in the tank position, the twelve-litre GIVI EASY06 adds a charging cable port. And for the same material and the same Canyon range but carrying a whole trip, the forty-litre GIVI GRT712C straps behind the seat.