I have some back issues and my doctor recommended to use a bike with a chair instead of a seat post. I have a old bike that I used for a trainer. I plan to cut the front part of it, turn the remaining part around (so the pedals turn in the right direction) and build a seat in front of it.

I'm trying to build the seat in front of it, to use as an indoor training rig.

Here is a simple schematic:

Some schematic

However, I'm having trouble figuring out the exact geometry of the seat. Can anyone recommend some resources/plans ?

The D size is fixed, I cant cut more from the bike seat post to lower it. I'm interested in determining the A angle, and the B/C sizes.

Edit: Just went ahead and cut everything from the bike except the rear wheel support and the pedals. First mistake: cut the D part too low, the pedals hit the ground.

However, after cutting, and sticking a 20mm board under D, it's almost usable with a kitchen chair. Only problem is that the trainer gets away from you when you push on the pedals, and lack of back support.


  • Your base board needs to extend under the chair, so you're attached to the trainer and hold it in place with your weight. If you're going to push really hard, it should be fastened to the seat
    – Chris H
    Commented Dec 20, 2019 at 11:50

1 Answer 1


Atomic Zombie has a bunch of DIY recumbent bike plans, many of which are based on cutting up existing bikes. This one seems like a reasonable starting point. I think that sitting in a regular chair might not give you full leg travel--recumbent seat bottoms are pretty short by comparison.

  • True, on my recumbent, if I lower my leg to place my foot on the ground, it goes down from my buttocks, it is not supported beyond that as it needs space to move while cycling. Best check out some photos or videos of recumbents.
    – Willeke
    Commented Dec 10, 2019 at 20:56

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