Knowing a bit about building bikes, if the spokes go from the hub to the smaller rim, then from the smaller rim to the bigger one, you will almost certainly never get that to run true.

Building a strong and true wheel is all about triangulation of the spokes to hub, and a rear wheel is offset to allow for the cassette, I would say it would be almost impossible to get it to work, and you would spend a lot of time achieving something that won't work.

Wheel building is an art, that isn't easy to achieve, and I certainly wouldn't start this way.

Edited By David Standing 1 on 11/05/2018 17:02:38

Back to the spacing. Yes a strip of paper works but you still have the problem of marking the right number of holes / spacing without ending up with a half a space at the end. It is the same as dividing for making unusual gears which you might be able to look up. A common method is to use a perforated strip, eg builders strip then cope with the diameter not fitting your wheel by packing with cardboard before marking.

Mick

I can see now why you wanted to try it – and I had no intention of doubting that you love your son.

I've built a few wheels myself over the years and so know a little about them. As they are a highly-stressed and safety-critical item, it would be most unwise to risk his well-being by fitting a wheel that I believe would be fundamentally flawed in its integrity. Perhaps I phrased my comment badly, but I am deeply concerned that you are proposing something which you might regret if it goes – well, I suppose "pear-shaped" would be an adequate description.

i know nothing about wheels, but i like your curiosity, if you are not going to use it as a wheel would your son settle for a polished sold band between the inner rim and outer rim which could be customised in some way, just a thought

Am i to understand that you will use the flange part of the rim of the smaller wheel to mount the spokes for the larger wheel? That would seem to be the only way it would work. Technically there would appear to be no problem doing it, as long as you can get the holes drilled in the correct locations. One issue will be the crossover of the spokes, assuming you are using crossed spokes for the outer rim and not radial. With the shorter spokes they will be stiffer and so you will probably find it hard to cross over more than once, so the outer rim will not be as rigid as one having two-cross or three-cross spokes. Also the rim of the inner wheel would not be as rigid as the hub of a normal wheel, so it will flex more leading to greater difficulty in tensioning the spokes and getting the outer wheel to run true.

Still, it would be possible and an interesting exercise for your son to pursue. Let us know how he gets on.