Why is there no 6 speed IGH

[rofan]

Technical question:
There are so many variations between 2 and 14 gears (no 6, 10,13)
Why is/was there no 6 speed?
The combination of 2 planetary gears should make it possible.
Any knowledge or idea?

[simonineaston]

I suspect that any answer worth reading will be long, mathematical and - dare I say it - slightly dull! However, Sheldon is informative as usual. http://www.sheldonbrown.com/internal-gears.html
Easier, surely, to simply accept that while there are 2, 3, 4, 5, 7, 8, 9, 11 and 14 speed hubs available, 6 speed hubs are not!
Alternately, you can buy a hub with an infinite no.s of ratios, instead. http://www.joulebikes.co.uk/nuvinci/nuv ... train.html

[Brucey]

Sorry if this is long, mathematical, or a bit dull....

I think that a 6s gear (done the right way) could be lightweight, compact, efficient, and a nice gear to use, too, in the same way as a SA 4s gear is nice to use; the 4s gear has direct drive in 3rd giving two low gears and one high one, and a good efficiency in the most used gears.

So if you had a 3s gear in series with a 2s reduction drive , you could have direct drive 5th, one high gear and four low ones; potentially a good arrangement for touring, utility and carrier cycles etc., maybe offroad use too...

I can think of two ways of doing this, with either separate or overlapping gear ranges.

For separate gear ranges suppose 0.5 x (0.80, 1.0, 1.25) gives gears of 0.4, 0.5, 0.625, 0.8, 1.0, 1.25 (312% range) or in gear inches with (say) a 65" base gear
26.0"
32.5"
40.6"
52.0"
65.0"
81.2"

For overlapping gear ranges say 0.66 x ( 0.75, 1.0, 1.33) give gears of 0.5, 0.66, 0.75, 0.88, 1.0, 1.33 (266% range) or in gear inches with (say) a 62" base gear

31.0"
40.9"
46.5"
54.6"
62.0"
82.5"

An alternate (wide) separate gear range could be 0.45 x (0.75, 1.0, 1.33) gives 0.34, 0.45, 0.6, 0,75, 1.0. 1.33 (394% range) or in gear inches with (say) a 62" base gear

18.6"
27.9"
37.2"
46.5"
62.0"
82.5"

so with even a small number of ratios available there are various strategies that can give gears with different distributions according to need. If (say) there were two choices of reduction gear and two choices of 3s gear ratios I think you could have a modular system with at least three different configurations that would give sensible sets of 6 gears that are distributed in different ways. [The fourth combination I think would give duplicate or near duplicate gears.]

So yeah, a 6s gear, why not?

cheers

[simonineaston]

Sorry if this is long, mathematical, or a bit dull....

Glad I didn't put you off replying!

[rofan]

simply accept that while there are 2, 3, 4, 5, 7, 8, 9, 11 and 14 speed hubs available, 6 speed hubs are not!

I do not want to buy one, I am perfectly satisfied with my 2, 3, 4, 5, 7, 8, 9, 11 and 14 speed hubs + NuVinci.
But I wonder, is there a technical or economical aspect, that the main producers did not built one?

That it is possible, I know.
And I like to read detailed answers
Thanks Brucey

[Mick F]

I wonder (yes I wonder - old song!) if the pursuance of more and more gear ratios, just skipped No6 ?

RN sailors' song:
"Oh I wonder, yes I wonder,
If the Joss Man made a blunder,
When he made this draft chit out for me?"

.... the song goes on a bit from here, but it's not suitable for publication.

[[XAP]Bob]

I've got a 6 speed (well, if you count like the dedangler people do...

3*2 with the middle of both sets being the same is counted as 5 - because IGH people can count, unlike people reliant on piles of sprockets

[Mick F]

Yes, I had a 6sp when I was a yoof on my Hercules.
I had a 3sp SA and I fitted two cogs to it with a Huret Svelto derailleur and clamp-on friction lever.

I can't remember the actual cogs and chainring combination, but I can remember the sequence.

Big Cog:
1st, 2nd, 4th.

Small Cog:
3rd, 5th, 6th.

[[XAP]Bob]

it's an SA 5 speed - with a standard 3 speed, but two selectable sets of planets - so:

3spd position / Planetary selection
1/2
1/1
2/1 = 2/2
3/1
3/2

[rofan]

it's an SA 5 speed - with a standard 3 speed, but two selectable sets of planets -

can you remember the model/type?
tks

[Brucey]

a 5s SA hub is not a 6s hub.... - two of the ratios will always be the same, both being direct drive...

The 2x3 hub I propose will truly give six different gears.

Mick's 2x3 gear setup is similar to many others that have been used over the years. Brompton presently use a similar 2x3 system on some models. If the 2x drive ratios are reasonably close together (as in Mick's case) then the ratios overlap in the same way as in the example that I gave earlier. In the case of the Brompton the 2x ratios are very close together and the x3 ratios are not, so the 2x shifter is used on every shift.

Versatile though it is, a combined conventional derailleur/IGH solution is always going to be a messy one because you still need a chain tensioner in there. On a Brompton this is arguably OK because there has to be a chain tensioner in that design anyway. But on other bikes it is just more sticky-outy junk to get dirty, bent etc. Those tiny pulleys are always noisy, too, and part of the attraction of an IGH (i.e. is that it is externally simple) is lost.

I think that incorporating a x2 drive inside a standard SA shell along with the x3 drive ought to be possible; after all there is room for a generator or a brake inside a 3s hub... and I think the resulting arrangement could be lighter in weight and simpler than having an additional derailleur, thus retaining the basic attraction of an IGH.

cheers

[[XAP]Bob]

a 5s SA hub is not a 6s hub.... - two of the ratios will always be the same, both being direct drive...

I did say I was being cheeky, and counting gears like a dedangler manufacturer...

[Brucey]

a 5s SA hub is not a 6s hub.... - two of the ratios will always be the same, both being direct drive...

I did say I was being cheeky, and counting gears like a dedangler manufacturer...

yeah, I thought so but I wondered if others were going to see it that way...

cheers

[SA_SA_SA]

Wouldn't a step-up 2x stage be more efficient?

[[XAP]Bob]

it's an SA 5 speed - with a standard 3 speed, but two selectable sets of planets -

can you remember the model/type?
tks

Just says 5 speed hub, alloy cps hell on the hub. Oil port as well.