Review: Alpkit Koala Exo-Rail seatpack

Pros: great build quality, improves bag stability. Cons: limited compatibility.
Ralph Jessop reviews the bikepacking seatpack-and-rail bundle that limits sway and works with a dropper

Alpkit’s Koala is a bikepacking seatpack in 7- or 13-litre sizes, while the Exo-Rail (currently on sale at £80 down from £95.99) is an anti-sway support for it that extends from the bike’s saddle clamp. Getting both together as a bundle saves £11 compared to buying them individually. I tested the 7-litre Koala (note: the 13-litre pack is pictured), which is a good size for a day-bag carrying a repair kit, waterproof jacket, pump, and some snacks, or stuffed full for a trip. It’s easy to make it smaller by rolling it up more.

The Exo-Rail is only compatible with fore-and-aft twin-bolt seatposts. Fitting may require the supplied extension bolts. These didn’t have the same chamfer at the head as the ones on my Fox or Thomson posts; it’s easy to sort if you are handy with a file. Once fitted, the Exo-Rail increases the saddle height by the thickness of the rail and spacer block – worth considering if your dropper is inserted to the collar.

There is a lot less wag from the pack than the non-Exo-Rail version, and less tightening of the straps is required to stabilise the load. A loaded pack will, however, exaggerate any free-play in your dropper. On my full suspension bike, the pack hit the rear wheel under sag in the fully-up position. On my hardtail, it just missed the rear wheel on full drop. It was perfect with a rigid post.

When using the pack on a dropper without the seatpost strap fitted, the loaded pack hits the slider part of the post. In time this could wear the surface. As a workaround, I tried the pack with the seatpost strap fitted and some electrical tape around the slider to protect it. This kept the pack a lot more stable but the tape hit the dropper post seal when the saddle was dropped.

Removing the bag from the bike involves unthreading the straps from under the seat and sliding it off. The bike is then left with the metal loop of the frame out over the rear wheel. I wouldn’t fancy riding hard with the bare frame sticking out so it would mean removing the ExoRail frame if you choose to ride without the bag!

The build quality is great. The bag’s new locking-strap buckles are an improvement, and the Exo-Rail has shown no signs of twisting or rust and no creaking or loosening from the block.


Adding the Exo-Rail to the Koala bag is a big improvement. It works well on a rigid post and, with care and enough clearance, on a compatible dropper.

Other options

Specialized Burra Burra Stabilizer Pack £132 (currently on sale at £96.99)

In the middle of the Koala sizes, at 10 litres, with a similar frame idea. Not dropper-post compatible.

Rockgeist Gondola from $120 + P&P

A simple, lightweight design that’s customisable, the dropper-compatible Gondala doesn’t use additional rails. Size: 4L or 5L.