3 Speed Hub Gear With a Triple?

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MacBludgeon
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3 Speed Hub Gear With a Triple?

Postby MacBludgeon » 15 Feb 2010, 6:01pm

Was along at the bike shop today and chatting about hub gears etc, the mechanic mentioned he runs a SA 3 speed with a triple chainring. The thought fired my imagination, is this a 'good' idea or total insanity?:-

Leave my existing 30/42/52 triple
Rear wheel with the SRF3 spaced to 130mm(I have the 175 axle version, 126.8 OLD, I've checked)
Add chain tensioner or leave an old RD on
Fit a 21t 3/32 cog and 3/32 chain
42t ring in perfect chainline
gives a 29-90 inch range with the middle ring on the magic 2:1 ratio

Apart from upsetting the fashion police are there mechanical reasons this wouldn't work?
nuns, no sense of humour

PW
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Re: 3 Speed Hub Gear With a Triple?

Postby PW » 15 Feb 2010, 6:11pm

I'd be a bit wary of gearing it that low. Officially the AW 3 speed isn't supposed to go below a ratio of 2/1 chainring to sprocket. They are fairly robust and I've used a double chainring/double rear sprocket setup 48/36 X 18/21 without wrecking anything but below that there's a chance of ripping the teeth off the internals.
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gaz
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Re: 3 Speed Hub Gear With a Triple?

Postby gaz » 15 Feb 2010, 6:12pm

I've seen it done, with a wide range six block thrown in on the back for good measure.

As PW says there are mechanical issues.
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stevew
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Re: 3 Speed Hub Gear With a Triple?

Postby stevew » 15 Feb 2010, 6:22pm

Seem to remember SA hub gears have a minimum ratio that one shouldn't go below, but what it is I haven't a clue !
All to do with not putting too much torque through the hub gear mechanism.
But if the LBS mechanic has done it you at least have a model to judge your potential set up on.
And of course Sram do market a 3 speed hub gear with a 8 speed cassette which is sometimes used with a triple chainwheel.
So taking all that into consideration my hunch is that it will work, but don't quote me ! !
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531colin
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Re: 3 Speed Hub Gear With a Triple?

Postby 531colin » 15 Feb 2010, 6:28pm

Well, it would be interesting! Sturmeys break when people run them badly adjusted so they skip, I wonder if leg power could break it if its properly in mesh?
You could get advantages of both systems, but also disadvantages. Chain suck! Yuk!
With a 2:1 middle gear, I guess this is for off- road?

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hubgearfreak
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Re: 3 Speed Hub Gear With a Triple?

Postby hubgearfreak » 15 Feb 2010, 6:59pm

macb, you're as mental sa mickf :lol:

however, having said that, the only reason not to do as you propose is the problem of running drive to hub ratio of 1.4:1, instead of the recommended minimum of 2:1. the worst i can see happening is that you wreck the rear hub, and they're not too expensive to replace the innards of are they?

give it a go, and it goes without saying that you'll let us know what happens 8)

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cycleruk
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Re: 3 Speed Hub Gear With a Triple?

Postby cycleruk » 15 Feb 2010, 7:24pm

From the above - am I right in thinking that you are not supposed to use a chainset with less than double the teeth of the rear sprocket?
You'll never know if you don't try it.

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hubgearfreak
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Re: 3 Speed Hub Gear With a Triple?

Postby hubgearfreak » 15 Feb 2010, 7:30pm

that's sturmey's recommendation, yes

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Mick F
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Re: 3 Speed Hub Gear With a Triple?

Postby Mick F » 15 Feb 2010, 7:48pm

hubgearfreak wrote:macb, you're as mental sa mickf :lol:

Yep.
Mental, that's me!

I have a Raleigh Chopper - don't ask! - with a 52/42 chainset and a 28/18 double sprocket arrangement at the back coupled onto the 3sp Sturmey Archer.

It can be done, and providing you have a mechanical mind, anything is possible.

Bottom gear is 22.5". It seems to work quite well.
Mick F. Cornwall

MacBludgeon
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Re: 3 Speed Hub Gear With a Triple?

Postby MacBludgeon » 15 Feb 2010, 7:51pm

hubgearfreak wrote:that's sturmey's recommendation, yes


I've searched the SA website, downloaded the tech docs for the SRF3, and I can't find anything that mentions min/max ratios.
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hubgearfreak
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Re: 3 Speed Hub Gear With a Triple?

Postby hubgearfreak » 15 Feb 2010, 8:24pm

MacBludgeon wrote:I can't find anything that mentions min/max ratios.


maybe it's an urban myth then?
if you think about it, there must be a minimum below which you'll just start to shred everything up.
sorry, i can't remember where i read that it's 2:1 :oops:

MacBludgeon
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Re: 3 Speed Hub Gear With a Triple?

Postby MacBludgeon » 15 Feb 2010, 8:59pm

hubgearfreak wrote:
MacBludgeon wrote:I can't find anything that mentions min/max ratios.


maybe it's an urban myth then?
if you think about it, there must be a minimum below which you'll just start to shred everything up.
sorry, i can't remember where i read that it's 2:1 :oops:


No probs, I'll find it eventually, all the other hub gear makers mention minimum ratios but nothing on SA. I've read loads on Sheldon, including his home bred 63 gear bike. That was a 3 speed SA, with a 7 speed block and a triple chainring, only his looked professional, unlike the MickF sticky back plastic version :twisted:

This may just be a passing fancy but, now that I've looked at it more..........
nuns, no sense of humour

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hubgearfreak
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Re: 3 Speed Hub Gear With a Triple?

Postby hubgearfreak » 15 Feb 2010, 9:01pm

MacBludgeon wrote:This may just be a passing fancy but, now that I've looked at it more..........


i reckon you should give it a go, if for no other reason than just to be different :mrgreen:

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Mick F
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Re: 3 Speed Hub Gear With a Triple?

Postby Mick F » 15 Feb 2010, 9:05pm

Sticky Back Plastic?
The cheek of it!

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hubgearfreak
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Re: 3 Speed Hub Gear With a Triple?

Postby hubgearfreak » 15 Feb 2010, 9:22pm

you're right mick, it's more heath robinson.

when you're on your lejog, have you got a network of chap(ess)s with spare AW innards and bench vices for when the inevitable happens?
i'd offer, but you'd also be lost if you're anywhere near lincoln :lol: