Gearing question for recumbents.

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Tangled Metal
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Gearing question for recumbents.

Postby Tangled Metal » 16 Feb 2018, 8:57am

My recumbent seems to have a very folded up rear derailleur. I am new to riding it so haven't had it out of middle chainring and mid to small cog on the cassette. It looks like the derailleur will not move out enough to go to the larger cassette cogs. What is that about and how to correct it?

I know they're just standard mtb Deore derailleur but I thought coming to this section might get better advice.

BTW I've lengthened the boom by a few inches, as far as the front derailleur cable allows. The chain looks like it could allow more movement. I do need to lengthen the boom by replacing cable and looking at chain but putting it off until I've had a proper ride on it up and down hills on the road. Only done one flat off road ride.

PDQ Mobile
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Re: Gearing question for recumbents.

Postby PDQ Mobile » 16 Feb 2018, 9:37am

The chain has to be just the right length to accommodate pretty much all gear combinations.
If you are astute about gear selection ie. never use large front onto the larger rears then slightly shorter is ok.
It's just like a conventional bike except that the long chain enables more crossed chain lines without significant issue, for example.,the front "granny ring" can be used in combination with quite small rears.
It's handy in a steep place sometimes
If you've extended the boom then you almost certainly need to add links. Best is to run the bike hanging on a rope or on a stand, though all the gears. You can see what's going on then.
Last edited by PDQ Mobile on 16 Feb 2018, 9:54am, edited 2 times in total.

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[XAP]Bob
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Re: Gearing question for recumbents.

Postby [XAP]Bob » 16 Feb 2018, 9:48am

An inch of boom movement changes the chain length by two inches...

If you’ve moved the book you need to change chain length (or have an easy adjustvaddon)
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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Tigerbiten
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Re: Gearing question for recumbents.

Postby Tigerbiten » 16 Feb 2018, 11:12pm

On a recumbent you tend to use bigger range of gears than on an upwrong.
This means you'll tend to push the range limits of derailleurs.
So long as you can use big-big then you're fine even if small-small causes the chain to be slack/rub on the rear derailleur.
When I used full derailleur gears on my bent trike, I ran 48/36/22 front triple and 9/32 back block for a 5x range 12.5"-100".
This was the upper range limit of both derailleurs.

Now I use IHG front and back, I only need to take up chain for a 54/38 front double.

PDQ Mobile
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Re: Gearing question for recumbents.

Postby PDQ Mobile » 16 Feb 2018, 11:45pm

I am not convinced by Tigerbiten's large to large being necessary. I would never run that combination. There is no gain, no advantage. There's a middle ring!
Additionally a very tight chain line results in more resistance and noise too.

It is important that the low gears work well.
That the rear mech and chain have some tension left (just a bit) when on "smallest to (almost?) smallest"; say be able to go up 5 or 6 cogs on the rear.
There should be no risk of the chain looping or tangling.
You can't honk on a bent so the seamless operation of the low gears is crucial. Especially round here!!

OldBloke
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Re: Gearing question for recumbents.

Postby OldBloke » 17 Feb 2018, 12:42am

Tangled Metal,

Prop your bike/trike up so the back wheel can turn freely and run through all your gears while you crank by hand. Then you'll have an idea of what gear combinations work. On my trike I ran a 48/36/22 on the front and a 10-36 10 speed on the back with a 26" wheel. I couldn't use the large ring with the two largest cogs on the cassette without jamming up the derailleur. So I always had to keep track of what gear I was in.

It is easy enough to remove or add lengths of chain if you have a chain breaker and a couple of quick links.

Cheers

OB

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Tigerbiten
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Re: Gearing question for recumbents.

Postby Tigerbiten » 17 Feb 2018, 1:03am

PDQ Mobile wrote:I am not convinced by Tigerbiten's large to large being necessary. I would never run that combination.

If you cannot run the big-big combo and shift into it by mistake then something breaks ........ :cry:
And you're most likely to make that mistake when you're cold, wet and tired, exactly when you don't want to make it.
I know it's only a small risk but why take it.
As long as you have enough chain wrap around the small sprocket, then you can run the chain very slack in the small-small combo with no risk.

Brucey
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Re: Gearing question for recumbents.

Postby Brucey » 17 Feb 2018, 7:17am

Tigerbiten wrote:
PDQ Mobile wrote:I am not convinced by Tigerbiten's large to large being necessary. I would never run that combination.

If you cannot run the big-big combo and shift into it by mistake then something breaks ........ :cry:
And you're most likely to make that mistake when you're cold, wet and tired, exactly when you don't want to make it.
I know it's only a small risk but why take it.
As long as you have enough chain wrap around the small sprocket, then you can run the chain very slack in the small-small combo with no risk.


+1.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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Cunobelin
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Re: Gearing question for recumbents.

Postby Cunobelin » 17 Feb 2018, 7:38am

Forget the fact that it is a recumbent!!!!!

Derailleur positioning, tensioning and adjustment is exactly the same as for any other bike / trike

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[XAP]Bob
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Re: Gearing question for recumbents.

Postby [XAP]Bob » 17 Feb 2018, 8:09am

Except that the large large combination is no longer counter indicated by chain crossing..
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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NUKe
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Re: Gearing question for recumbents.

Postby NUKe » 17 Feb 2018, 8:19am

Big to big the derailluer should be in the 5 o'clock position as per any other bike. check the hp manual available on their site.
Just one other thought you bought second hand , check the capacity of the derailluer.
Capacity = difference big sprocket little sprocket plus big chain ring -little chain ring
Just in case the previous owner has put either larger rear sprocket or front chain ring.
NUKe
_____________________________________

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squeaker
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Re: Gearing question for recumbents.

Postby squeaker » 17 Feb 2018, 8:21am

Brucey wrote:
Tigerbiten wrote:
PDQ Mobile wrote:I am not convinced by Tigerbiten's large to large being necessary. I would never run that combination.

If you cannot run the big-big combo and shift into it by mistake then something breaks ........ :cry:
And you're most likely to make that mistake when you're cold, wet and tired, exactly when you don't want to make it.
I know it's only a small risk but why take it.
As long as you have enough chain wrap around the small sprocket, then you can run the chain very slack in the small-small combo with no risk.


+1.
+2. My first 'bent was a Challenge Mistral with 60/39 up front and 11-34 on the rear. IIRC I could only run the lower 6 rear sprockets before the mech gave up the tensioning challenge and chain noise increased. No chance of breaking it in 60-34 though ;)
"42"

UpWrong
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Re: Gearing question for recumbents.

Postby UpWrong » 17 Feb 2018, 9:19am

small/small combos can always be avoided by running a large/not-so-small combo. I always set up my bikes so that large-large is useable, and avoid using small/small if it causes too much slackness on return side of the chain.

PDQ Mobile
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Re: Gearing question for recumbents.

Postby PDQ Mobile » 17 Feb 2018, 10:36am

I understand the concerns about large to large.
Yet in practice it is a combination that I personally would never use.
Not on any bike.
It's a poor technique. (ducks!)
I don't select 1st gear in my car at 70mph.
The fact that on a recumbent the front mech is easily visible presents a constant visual guide.
And any tendency to approach those gears would be betrayed by stiffer rear mech lever and more transmission noise anyway.

The bike in question (SMGT) is a touring bike and it needs to be able climb steep hills laden to fulfill that purpose. Something like 60/34 combined with 11/34 that Squeaker uses is just not adequate.

So for my purposes, where I regularly climb really (1:5) steep hills, very low gears are simply essential.
Say 24/32 or34.

But then there's the other side of the hill!
The low wind resistance of the 'bent make really high downhill speeds a thrilling option.
To be able to generate power up into those speeds is great fun.

So to gain that kind of super wide range I "sacrifice" the ability to use the three larger rears with the large front (there's a middle!) and hence have a nice working set of (say 5or 6) really low gears that I can spin up steep hills.
Spinning is very important (essential?) on a recumbent in a steep place. It makes balancing much easier at low speeds.
All IMHO.

The lowland non-touring cyclist may well have other requirements though.

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[XAP]Bob
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Re: Gearing question for recumbents.

Postby [XAP]Bob » 17 Feb 2018, 10:40am

It might be bad technique - but it’s less bad for the longer chainline of a bent.

I add an IGH to spread the gears - a csrk3 SA hub gives a virtual ‘extra chainring’ at bithnends
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.