Why 20in(406) so more prevalent than 24in(507), when fold size similar?

[SA_SA_SA_SA]

Given that 20in wheel folders exceed the 90*70*30 strict national rules of carriage, so rely on individual Train companies own rules/ disgression, but are fairly bulky and only a fold little smaller than 24in wheeled ones, why are they so ubiqutious? Surely once above the magic size, you might as well have the biggest wheels for a given fold size....
(yes I know some companies specify folded size using wheel size but thats a stupid unit for folded size IMHO and if 24in folders (of similar folded size to 20in dahons) were the majority presumably they would say 24in max...)

eg Tern Node D16 (24in wheels) fold size of    41 x 85 x 80 cm
     Tern eclipse-tour(24in wheels) fold size of   42 x 89 x 76 cm
     Tern Link C7       (20in wheels)  fold size of  34 x 85 x 65 cm

Not a huge difference......

[cycleman]

A lack of decent tyres in 24 inch reduces the appeal of the larger wheel 

[Kim]

A lack of decent tyres in 24 inch reduces the appeal of the larger wheel 

Is that cause or effect though?

I suppose the popularity of BMX (and children's bikes based thereon) ensures a steady supply of all things 20", and the folders, recumbents and other exotica feed on that because it's a small wheel that still rolls reasonably well and you can get a decent choice of tyres and rims.

[cycleman]

A bit of both probably 

[drossall]

And 20 inch only fold a bit bigger than 16 inch. And 24 inch only fold a bit smaller than full size.

My Dahon Vitesse only marginally fails to meet the size restrictions. A 24-inch-wheel machine would fail more significantly.

You've got to stop somewhere.

[Ham]

Also, for all it might seem only marginally bigger, that's your impression based on your head looking at the linear dimensions on paper. Even the smaller one of the two 24" is 50% bigger in volume terms than the Dahon, I suspect that you would notice it significantly lugging around and trying to fit into spaces.

[drossall]

Agreed. My Dahon 20" is very obviously bigger than the ubiquitous Bromptons on our commuter trains.

[Ham]

I had to do it. The Tern above is double the folded volume of a Brommie.

How can I stop? My 20" Dahon (Mu Uno) is only 50% bigger than the Brommie

[SA_SA_SA_SA]

But I think volume alone is a bad measure:

I think width is more important (up to a point):

a brompton that was much wider but the same volume would be much less useful IMO.


NB the Dahon Ciao seems to have gone over to the smaller 20in size.....

[chagzuki]

My first folder was a 20" Dahon, then I got a Brompton. At some stage I will quite likely get rid of the 20" Dahon and replace it with a 24" folder as I agree that the trade-offs of folded size vs wheel size favour the 24" design. At the moment, however, most models tend to be rather heavy compared to similarly specced 20" bikes.