Gearing again

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slowster
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Joined: 7 Jul 2017, 10:37am

Re: Gearing again

Postby slowster » 25 Aug 2018, 9:42pm

Apologies if this is irrelevant in your case and/or has already been addressed in this thread, but is the middle ring of your new chainset so much smaller that the chain is too low with respect to the indented channel in your front derailleur which is designed to hold the chain when shifting from middle to outer ring?

Jan Heine covers this in a blog article here https://janheine.wordpress.com/2013/03/25/trouble-with-sti-triples/ (and I imagine the wrong chainline might also exacerbate this for a given size of middle ring):

Many front derailleurs for triples have a channel pressed into the inner cage. This is designed to lift the chain onto the big chainring when you upshift. It works only if the channel matches the position of the chain on the middle ring. A derailleur like this works only with a very narrow range of chainring combinations.

If you use a differently-sized middle ring, the channel no longer lines up with the chain as you start the shift. In the photo above, the channel is above the chain. The chain gets stuck below the channel, and it’s almost impossible to shift to the large ring.

The article goes on to advise using a front derailleur without the indent in such circumstances, and suggests the Shimano CX70 model, which it says can work with triples.

NetworkMan
Posts: 647
Joined: 25 Aug 2014, 11:13am
Location: South Devon

Re: Gearing again

Postby NetworkMan » 26 Aug 2018, 10:14am

slowster wrote:Apologies if this is irrelevant in your case and/or has already been addressed in this thread, but is the middle ring of your new chainset so much smaller that the chain is too low with respect to the indented channel in your front derailleur which is designed to hold the chain when shifting from middle to outer ring?

Jan Heine covers this in a blog article here https://janheine.wordpress.com/2013/03/25/trouble-with-sti-triples/ (and I imagine the wrong chainline might also exacerbate this for a given size of middle ring):

Many front derailleurs for triples have a channel pressed into the inner cage. This is designed to lift the chain onto the big chainring when you upshift. It works only if the channel matches the position of the chain on the middle ring. A derailleur like this works only with a very narrow range of chainring combinations.

If you use a differently-sized middle ring, the channel no longer lines up with the chain as you start the shift. In the photo above, the channel is above the chain. The chain gets stuck below the channel, and it’s almost impossible to shift to the large ring.

The article goes on to advise using a front derailleur without the indent in such circumstances, and suggests the Shimano CX70 model, which it says can work with triples.

I did address it in the thread I started earlier which I pointed out to the OP. Jan Heine is quite right about the shape of the FD but he is just too pessimistic when he says you have to use a Shimano sized chainset if you want to use an STI triple. Many people writing on here, myself included, have shown this to be false providing you keep the spacing and size of the rings close to the original ones. What's more Spa cycles must have sold hundreds of tourers with 48-38-28 chainsets using FDs intended for 50-39-30.
I always wonder with the Jan Heine articles if there is an inclination to want to sell you some Compass bicycles parts, in this case perhaps chainsets costing $415 - $515! Gosh - I could feed a family of four for at least a couple of weeks on that and have change left over for a Spa XD-2.

We need the OP to tell us just what he's done so that we can help further. The 50 mm chainline just doesn't make sense.

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RickH
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Location: Horwich, Lancs.

Re: Gearing again

Postby RickH » 26 Aug 2018, 12:51pm

To be fair, unless I've missed something in a quick scan through, Jan Heine only refers to problems with a different sized middle chainrings - i.e. a different middle to outer spacing.

In my experience it is best to stick as near as possible to the specified number of teeth gap even if the absolute number of teeth is different (for example, I swapped 53/42 on my Campag comp triple to 50/39 (both 11T), the inner swap was beyond spec 30 to 26 but that matters less (if at all) .

NetworkMan
Posts: 647
Joined: 25 Aug 2014, 11:13am
Location: South Devon

Re: Gearing again

Postby NetworkMan » 26 Aug 2018, 3:41pm

RickH wrote:To be fair, unless I've missed something in a quick scan through, Jan Heine only refers to problems with a different sized middle chainrings - i.e. a different middle to outer spacing

Nope - in the conclusions - A Shimano triple and STI means a Shimano stock chainset only. I call that plain wrong.
Let's wait for the OP to tell us more ....

Marcus Aurelius
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Joined: 1 Feb 2018, 10:20am

Re: Gearing again

Postby Marcus Aurelius » 26 Aug 2018, 4:32pm

Ultimately, if you’re struggling on hills, and you want to ride hills, working to up your fitness, rather than down your gearing is the best option. If you can stand on one leg, then on the other leg, independently, that’s as much ‘strength’ as you need for cycling. Improving your fitness and muscle endurance is what you need to do. A very effective way to do that is ride more hills and try to go faster up them, without down gearing.

molzor
Posts: 113
Joined: 21 Dec 2014, 12:34pm

Re: Gearing again

Postby molzor » 26 Aug 2018, 4:35pm

I bought a TD2 170mm 46/36/26 version, maybe this was a step too far from the recommended 50/39/30?
I also got a new BB which was a shimano un55, 113mm, 68mm.

my front mech does have a channel in the middle which lines up with the chain on the second ring. maybe it would help if this channel wasnt there.

I also adjusted the height of the mech to 2mm above the big ring.

molzor
Posts: 113
Joined: 21 Dec 2014, 12:34pm

Re: Gearing again

Postby molzor » 26 Aug 2018, 4:38pm

Marcus Aurelius wrote:Ultimately, if you’re struggling on hills, and you want to ride hills, working to up your fitness, rather than down your gearing is the best option. If you can stand on one leg, then on the other leg, independently, that’s as much ‘strength’ as you need for cycling. Improving your fitness and muscle endurance is what you need to do. A very effective way to do that is ride more hills and try to go faster up them, without down gearing.



This is all well and good. I appreciate the "if you are too cold you arent cycling hard enough" attitude. but i cycled with the old gearing for 4 months every day, across europe and back. at which point my fitness was pretty bloody good. and while i managed it, it wasnt ideal. so when it came to getting a new chainset, i thought why not drop it.

NetworkMan
Posts: 647
Joined: 25 Aug 2014, 11:13am
Location: South Devon

Re: Gearing again

Postby NetworkMan » 26 Aug 2018, 4:53pm

molzor wrote:I bought a TD2 170mm 46/36/26 version, maybe this was a step too far from the recommended 50/39/30?
I also got a new BB which was a shimano un55, 113mm, 68mm.

my front mech does have a channel in the middle which lines up with the chain on the second ring. maybe it would help if this channel wasnt there.

I also adjusted the height of the mech to 2mm above the big ring.

It may be a step too far but probably not.
First of all are you still saying the chainline is 50 mm rather than 45. Please measure again from middle ring to centre of downtube.
When you say shifts are stiff are you talking about upshifts? - presumably so.
Difficulty in shifting from middle to big could well be the problem I had at the end of my linked post. The chain tries to climb onto the big ring but before it gets there it jams as it leaves the region where the cage is wider. Is that happening? It's easier to investigate if you have a workstand. If it is happening then you need to raise the cage a few mm.

How about shifts from little to middle, are they stiff?

molzor
Posts: 113
Joined: 21 Dec 2014, 12:34pm

Re: Gearing again

Postby molzor » 26 Aug 2018, 5:13pm

NetworkMan wrote:
molzor wrote:I bought a TD2 170mm 46/36/26 version, maybe this was a step too far from the recommended 50/39/30?
I also got a new BB which was a shimano un55, 113mm, 68mm.

my front mech does have a channel in the middle which lines up with the chain on the second ring. maybe it would help if this channel wasnt there.

I also adjusted the height of the mech to 2mm above the big ring.

It may be a step too far but probably not.
First of all are you still saying the chainline is 50 mm rather than 45. Please measure again from middle ring to centre of downtube.
When you say shifts are stiff are you talking about upshifts? - presumably so.
Difficulty in shifting from middle to big could well be the problem I had at the end of my linked post. The chain tries to climb onto the big ring but before it gets there it jams as it leaves the region where the cage is wider. Is that happening? It's easier to investigate if you have a workstand. If it is happening then you need to raise the cage a few mm.

How about shifts from little to middle, are they stiff?





I just measured again, and it does seem to be 45mm! apologies for that confusion.

Yes it is difficult shifting up. from the small to the middle, but even more so to the top. I think this is because it seems I have to put a hell of a lot of tension in to make the derailleur reach across.

I will investigate where the cage is sitting and how it shifts up, maybe try and raise it a little as you said

slowster
Posts: 880
Joined: 7 Jul 2017, 10:37am

Re: Gearing again

Postby slowster » 26 Aug 2018, 5:28pm

molzor wrote:my front mech does have a channel in the middle which lines up with the chain on the second ring

Do you just mean that the channel lines up with the chain when the chain is on the middle ring and you are not in the process of changing gear, or is the channel also in the right position/height when actually shifting, i.e. the channel picks up the chain?

FWIW, I have a Spa Super Compact double which uses the TD chainset. With a UN55 115mm bottom bracket, my chainline is 47mm (based on the 'outer' ring, i.e. what would be the middle ring if the chainset were set up as a triple), which is consistant with NetworkMan's chainline for his triple and BB and with Spa's recommendations. It doesn't make sense that your chainline with effectively the same chainset and a 113mm BB is 50mm.

Edit - Crossed posts with your correction of your chainline.

molzor
Posts: 113
Joined: 21 Dec 2014, 12:34pm

Re: Gearing again

Postby molzor » 26 Aug 2018, 7:35pm

I have been playing with the height and angle of the front mech in regards to the channels. It doesnt seem to make much difference. It still requires extreme tension in the cable and a very stiff shift to make it change up. You couldnt really use it like it is.

I wonder if the channels in the mech are just meant to be for 30/39/50? They seem quite spaced out, and you cant actually buy different size chainrings for the matching tiagra chainset which I was using previously, so there could be a reason for that.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Gearing again

Postby Brucey » 26 Aug 2018, 7:47pm

all else being equal shifting force will also be increased if you move from ramped/pinned rings to some with fewer ramps/pins etc. is this the case? (there are different chainring options on chainsets from spa)

Also, is the shifter/cable old, poorly lubricated, or badly routed (esp via a BB guide)?

cheers
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molzor
Posts: 113
Joined: 21 Dec 2014, 12:34pm

Re: Gearing again

Postby molzor » 26 Aug 2018, 7:51pm

Looking at the front mech in depth, there appears to be different versions of the same mech, the one they are currently selling is listed as 4703b
Image

But my one looks more like this
Image

slowster
Posts: 880
Joined: 7 Jul 2017, 10:37am

Re: Gearing again

Postby slowster » 26 Aug 2018, 7:55pm

Is the stiffness only felt when the cage comes into contact with the chain and presses against it, or is it felt before then?

You haven't by any chance re-attached the cable to the front derailleur on the other side of the pinch bolt?

Brucey
Posts: 35240
Joined: 4 Jan 2012, 6:25pm

Re: Gearing again

Postby Brucey » 26 Aug 2018, 7:58pm

read the FD model number and double-check what the chainring interval is meant to be with your mech. Compare with the interval you are using and act accordingly.

Note also that the FD is meant to be used with the chain entering it at within a certain range of angles; toe in or toe out can alter the angle one way and the included angle between the chainstay and seat tube (as well as variations in cassette and chainring sprocket sizes) alter it in the other. Both can affect front shifting.

cheers
Last edited by Brucey on 26 Aug 2018, 10:04pm, edited 1 time in total.
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