Rinko bag
This Rinko bag should let you take your bike on most trains without a reservation. I’ve successfully used it myself in Germany and Switzerland, it should also be okay in France and Spain, and probably most of Europe. But I don’t guarantee anything.
The bag is as minimalist as it gets, and designed with packability in mind. It rolls up to about the size of a coke can, so you can bring it on a bike packing trip. I use a high quality rip-stop to maximise durability at a low weight, but it’s an ultralight bag and it should be treated as such.
The bag is more of a cover, you carry the bike by the supplied shoulder strap that attaches to the head tube and seat post. This means the bag itself isn’t under any strain, which is why it can be as light as it is. You need two Voile straps to strap the wheels to the frame, and maybe an old towel or dirty t-shirt to protect the paint.
I use the bag as follows:
1. Take off the derailleur.
2. Take off the bars.
3. Remove the wheels.
4. Lay the bag flat on the ground.
5. Set down the frame in the opening of the bag.
6. Strap wheels and bars to the frame.
7. Pull bag around the frame.
8. Fit the carrying strap.
9. Close the bag with the Velcro.
The bag measures 146x100cm laid flat, it fits my size L ATB with 29×2.35” tyres and a rear rack. The packed size including shoulder strap (excluding Voile straps) is approximately 9cm diameter and 15cm high.
I can’t stress enough that this is an ultra-light bike carrying solution. It provides no protection for the bicycle and the fabric will not withstand stress. That means that sliding your bike across a train platform results in a torn bag and scratched paint. However, it fits in a jersey pocket / takes up maybe a quarter of a frame bag and lets you travel with your bike without reservations. I take no liability for damaged bikes or missed connections, and do not provide warranty for wear and tear.