[Closed] How many gears do you need? Internal hub musings... engineers wanted 🙂

So a bling sturmney archer then?

I guess so... pretty much the [url= http://www.sturmey-archer.com/products/hubs/cid/3/id/39 ]SX-RK3[/url] but a lot bloody lighter than 1.2kg!

Maybe you should run a triple up front with a single gear at the back and a mech as a tensioner?

nah... I like the neatness and look of a singlespeed 🙂

I've never done any 'proper' biking with hub gears but my experience from my old 7 speed Nexus work bike was the same as yours- I only ever used 1, 4 and 7. I think a (very) wide ranging 3 speed hub that was light(ish) and not overly expensive would be a very tempting proposition...

Like the idea. My setup on my SS is 32:16 but as you say a gear either side of that would be ideal. SOmething like a 28:18:12 would suit me.

The only thing is that if the gear ratio was fixed by the manufacturer the jump between gears would be quite large and depending on ability could mean it is not the best. If there was a way you could set the ratio yourself that would be sweet but engineering wise a nightmare!

I think it would have to be superlight to get me away form the simplicity of SS, but like the concept.

yep, being able to set the ratios yourself would be a great plus... I'm no engineer, have no idea if this'd be possible, but whilst we're dreaming... 😉

Similar discussion here.
http://www.singletrackworld.com/forum/topic/rohloff-or-alfine-11

I think a lighter Rohloff with less gears would be ideal.
Rohloffs seem to be aimed at touring cyclists. I guess if you're riding a heavily laden bike up a mountain pass it's nice to be able to pick exactly the right gear for the gradient with 13% steps between gears.
On a mountain bike where the terrain changes a lot more quickly and there's only a few seconds between steep down and steep up, I'd be happy with half the gears and twice the step between gears, as long as there was the same overall range and it weighed less.

grrrr... I want to build one, but no idea how or where to start! I wish I was smarter and had access to CNC machines etc! 🙁

Eh? Is the shifting slow or something?

Bicycles are something where loads of closely spaced gears are really very useful - most people don't have a huge range of RPMs where they're developing good power. In an ideal world, you'd have a CVT.

Or is it a case that the people who've tried hub gears out have switched from singlespeeding, and are used to working over big rev range?

I could mince with that. Granny climbing gear, middle work gear and overdrive for the road... other way to do it would be a three speed HammerSchmidt type thing without the AM/FR/DH bulk 8)

The modern S-A 3 speed hub is very smooth and it's nice and light. I use one on my roadbike. It has all the gears you could possibly need.

1 for uphill
1 for the flats
1 for downhill

The middle gear is direct drive so it's just like a single speed there - minimal transmission losses.

I have been tempted to squeeze an mtb frame in to 120 OLD to try it as a mtb gear, but I haven't yet worked out why I would need gears on a mtb. 🙂

I've got an S3X as well - it's a heavy bugger, but apparently more robust. It would be possible to put a WI freewheel on it and have a strong mtb 3 speed. There's no disk mount, but I suspect a bit of playing around with the S-A parts list would make that possible.

(BTW I have an SX-RK3 as well, and it's a lot heavier than 1.2kg 🙂 )

Or another take on the problem...

http://www.kinetics.org.uk/html/mountain_drive.shtml

?

[i]"Eh? Is the shifting slow or something?..."[/i]

No, the twist shifter used on a Rohloff is very quick, especially if you want to shift several gears at once, even when stationary.

More gears will always be better, all other things being equal. They're not equal though, it's a compromise between number of gears and complexity and weight.
Most bike manufacturers have settled on 3x9, although many individuals go for 2x9, 1x9 or singlespeed because they think simplicity and weight are more important than range of gears.

3 gears would be awesome.

a little twiddly one to get you up steep things.

a big pushy one for fast flat bits.

a 2:1 for everything else.

and surely that could be made a lot lighter than an alfine? - 8 less cogs for a start...

i know you can get something like this, but i've not seen one that's robust enough for mountain biking.

edit: a quick look at the sturmey archer website reveals the SX-RK3, with 6 holes for a disc!

but 1400grams?! - what's it made of? - osmium?!

and it's £250!

I dont think I get it. Well I sort of do, but don't. I like singlespeeding too. But I like my geared bike. This would just be a half-way-house that would be odd. If you're having gears you might as well have a good selection and use them all, why would you only use a couple?!

but 1400grams?! - what's it made of? - osmium?!

that's what I wondered as well, maybe it's depleted uranium or something?? 😆

I wonder if you could take the internals from a S-A 3 speed hub and fit them into a better/lighter/disc compatible shell? Also, maybe swap the axle for Ti or something to go lighter again?

I dont think I get it. Well I sort of do, but don't. I like singlespeeding too. But I like my geared bike. This would just be a half-way-house that would be odd. If you're having gears you might as well have a good selection and use them all, why would you only use a couple?!

I only want 3... well, I want them all, but I only [i]need[/i] 3, to keep my imaginary IGH nice and light and as close to a SS as possible...

Although the hub won't be light, ltll be the internals that add the weight.

What you want could be made but the market would be so small as to make it financially pointless

Rohloff say they can't make one that's lighter by simply removing gear ratios. Apparently it's more complicated than that.

I think Rohloff use three epicyclic gear units inside the hub.
By combining the way they step up or step down the gearing, they give 14 different gears.

To get the same range of gears with less ratios would not simply be a matter of leaving some of the cogs out to save weight. It would take a complete redesign.

As thepodge says, the number of people who would want to buy it would never cover the development cost.

well, sturmey archer make one, and i'm sure it would be lots cheaper and lighter if it wasn't made from a Uranium/Osmium alloy.

thepodge - Member
Although the hub won't be light, ltll be the internals that add the weight.

What you want could be made but the market would be so small as to make it financially pointless

This is the key thing. Very few people want a light three speed hub.

even fewer people want a VERY VERY heavy 3-speed hub... but clearly enough for S-A to think it's worth making.

three speed HammerSchmidt type thing without the AM/FR/DH bulk

I'd buy that.

36-32 gets me up 95% of climbs
36-20 singletrack
36-12 road

I'm looking at my worn cassete at the moment and wondering what the point of £50+ cassetts is when they only last a few months. Time to MTFU and go singlespeed.

ahwiles - even fewer people want a VERY VERY heavy 3-speed hub... but clearly enough for S-A to think it's worth making.

I would say that the average SA user has no concern about their weight, they just like their fit and forget ability. plus if you have a low enough gear weight becomes less of an issue so the hub kind of counteracts its own faults.

I also imagine (though I could well be wrong) that the SA hub was cutting edge when it was released but has not been updated with the times.

I'm looking at my worn cassete at the moment and wondering what the point of £50+ cassetts is when they only last a few months. Time to MTFU and go singlespeed.

Or not spend over 50 quid on a cassette...

http://www.chainreactioncycles.com/Models.aspx?ModelID=5045

but those cassettes weigh more than cornwall.

hang on, claimed wait: 230grams? - my 'internet lies' detector just exploded...

I was having the very same musings just yesterday. The Rohloff hub is incredibly heavy. After nearly a year of ownership and 1100+ Peak District miles I still cannot get over the weight of it. It is like carrying a heavy stone on your rear axle. Jumping on my Orange G3 SS is a revelation.

For climbing and getting up to pace I use nearly the full range of gears. I don't *think* of which gear I'm in, just use the right one for the job and keep on moving - so I do make much use of the range. But in more steady state environments I'd reckon I could get away with just 3 or maybe 4 gears... and to have a super lightweight hub in that format would be brilliant.

I've been toying with the idea of a Nuvinci hub http://www.fallbrooktech.com/nuvinci.asp, but they make the Rohloff look lightweight. Where are all the materials scientists who could make this stuff from superlight metals???

would this do you?

[img] [/img]

[url= http://www.shimano.com/publish/content/global_cycle/en/us/index/products/0/nexus/product.-code-SG-3D55.-type-.html ]3 speed nexus with disc mount[/url]

used on some specialised hybrids

What's the gear range though ? That's more important than the number of gears.
What most people seem to be looking for here is a hub gear equivalent of three chainrings and one rear sprocket, or 3rd, 7th and 10th on a Rohloff.
One chainring and three adjacent rear sprockets or 6th, 7th and 8th on a Rohloff isn't much use.

ratios for hub gears

http://www.sheldonbrown.com/gears/

3 speed normally jumps of 33% up and 25% down

on the nexus inter with 32 chainring, 16t sprocket on 2.1 26er tyres would give:

Gear Inches approx of 38", 52" and 71" (middle being 1:1)

for comparison...

32tx12t would give you 70" 32x16t give 52" and 32tx20t would give 41"

So, compared to a Rohloff with its 13% steps, that's roughly equivalent to 4th, 7th and 9th.
A bit better than a singlespeed and probably a bit lighter than a Rohloff, but I can't see it catching on for mountain bikes.

Right. My idea was two chains, one on each side of the bike with different ratios, with a centrifugal clutch inside the rear hub that would flip over automatically above a certain speed. When one was not in use it'd just spin freely. It'd look just like a singlespeed except on two sides. No shifters, no giant hub, no cables.

How does that sound?

How many gears do you need? Internal hub musings... engineers wanted 🙂

ONE! 😉

By the time you've added up the weight of the centrifugal clutch and the two chainrings, chains, sprockets and tensioner, you might as well run 1x9.

You want Retro Direct!

[img] [/img]

http://en.wikipedia.org/wiki/Retro-Direct

Right. My idea was two chains, one on each side of the bike with different ratios, with a centrifugal clutch inside the rear hub that would flip over automatically above a certain speed. When one was not in use it'd just spin freely. It'd look just like a singlespeed except on two sides. No shifters, no giant hub, no cables.

How does that sound?

try:

http://en.wikipedia.org/wiki/Retro-Direct
/p>

though you do have to pedal backwards to get one of the gears.

there is also the 2 speed kick back SA hub - change gear by a quick kick back on the pedals - doubt it would be so good offroad with frequent brake etc

clubber! doh beat me to it..

i think the nexus 3 speed looks a good bet

Oooh! Great minds...

A bike actually using it:

http://kentsbike.blogspot.com/2008/11/building-retro-direct-drive-bicycle.html

and there's a load of vids:
http://www.google.co.uk/search?q=retro+direct+bike&hl=en&prmd=v&source=univ&tbs=vid:1&tbo=u&ei=cRB9TMr9MIqQjAf99O3TDg&sa=X&oi=video_result_group&ct=title&resnum=5&ved=0CDMQqwQwBA

By the time you've added up the weight of the centrifugal clutch and the two chainrings, chains, sprockets and tensioner, you might as well run 1x9

a) no and b) weight isn't the point.

It'd be like singlespeeding except not spinning out on downhills and roads. And it'd be automatic.

I think it's an ace idea.

Brompton now have a wide range 3-speed hub that could be rather neat. Doubt it's MTB compatible though...

Brompton now have a wide range 3-speed hub that could be rather neat. Doubt it's MTB compatible though...

nope only 120oln... it is just a SA hub with slightly diff ratios

though it combined with their 2 speed dérailleur could be neat but would require work..

still think the disc shimano inter nexus is the best bet

thepodge - Member
...I also imagine (though I could well be wrong) that the SA hub was cutting edge when it was released but has not been updated with the times.

Not much to update in a light hub that's good for 50,000 miles, but it has been done.

is there no way interal hubs could be made lighter ?

is there no way interal hubs could be made lighter ?

possibly, but essentially they are almost solid lumps of metal.

but are they *that* bad?

compare a rear hub + cassette + dérailleur weight

A 3 speed S-A weighs slightly over 1,000 grams. When you compare this to a derailleur hub and the weight of the cassette and derailleur, it's not a great difference.

Especially when you consider the S-A hub will still be going strong long after you have worn through several sets of derailleur hubs and cassettes.

[i]"It'd be like singlespeeding..."[/i]
No, it'd be like twospeeding with a more complicated alternative to a two speed derailleur. 😉
I like the idea, but I don't see how it could be made to work.
All gear systems need the power to be reduced while the gear shift takes place.
Easy enough on a manually controlled derailleur or hub gear for the rider to back of a bit while they make the shift.
Not so easy on an automatic where the rider may not be expecting a shift.

If you shift from 7th to 8th slowly on a Rohloff while pedalling lightly, it will momentarily engage 14th.
This is intentional. The gears are effectively in two ranges, 1st to 7th and 8th to 14th. Going from top gear in the low range to bottom gear in the high range, it's safer to have the hub engage high range first so that the rider hits a sudden resistance to pedalling in 14th rather than engage the low gear first and suddenly hit almost no resistance at all in 1st.

A centrifugal gearbox would need to do something similar, especially as the rider may not be aware that it is about to shift gear. Catching the rider unawares with a neutral between gears, however brief, wouldn't be acceptable.
It would also need to be designed so that it shifts down at a slower speed than it shifts up.
Supposing you wanted it to change gear at 15km/h.
If the rider is riding at about 15km/h, it will be constantly shifting up and down.
Somehow, you would need to make it shift up at 16km/h and down at 14km/h.

StumpyBlurRider - Member
is there no way interal hubs could be made lighter ?

It's on my list of future [s]projects[/s] bodges.

There's a number of hefty bits of steel in there. Things like the lhs end and the bit that carries the planetary gears. I am contemplating a bit of drillium, but if you mix too much drillium with steel you create a new alloy called disintegratium.

If I had any competency on a lathe I'd try turning up alloy replacements for some of the heavier bits. Titanium would be better for niche points though 🙂

If I had any competency on a lathe I'd try turning up alloy replacements for some of the heavier bits. Titanium would be better for niche points though

some of SA alloy shell hubs are heavier than the steel shell versions

The steel 3 speed hub is 100g heavier than the alloy one and it's about the same for the 5 speed.

All gear systems need the power to be reduced while the gear shift takes place.

Not really. This would be like the VW DSG gearbox, where you've (effectively) got two gears each with its own clutch, and as one clutch comes out the other goes in.

Good point about downshifting at a different speed to upshifting though. That could be arranged I am sure, but it'd make the innards a lot more complicated than simply spinning weights.