28-38-48 swapped to 22-32-42 - FD shift problems

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Sweep
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by Sweep »

How did you get on with this howfar?

I ask because I may have a related issue.

I will wait awhile to see if you post and then post my related issue on the same thread.
Sweep
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CREPELLO
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by CREPELLO »

Sweep, we may not know when Howfar might reply, or whether the fix would be applicable for your bike.

Is it the same issue? From the Alivio thread you say you're using an Alivio MTB FD, whereas Howfar was using a Sora road FD, so not directly comparable really.

What's the problem?
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Sweep
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by Sweep »

I was wary of hijacking a thread crepello, particularly as the bike in question isn't with me at the moment so I can't offer immediate feedback on any kind suggestions.

When I have a mo I'll start a new thread.
Sweep
howfar
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by howfar »

It's my day off today so I can update you quickly!!

Still not got round to putting an MTB mech on the Randonneur so still have the same issue - I tried the 22-32-42 chainset on my commuter which has the Deore MTB FD and friction trigger lever. 7 speed cassette on the back 11-28.

Guess what? Still hesitant to shift down.....!

It's a stiff aluminium frame - so my assumption that the whippy 25" Randonneur frame under load and bending is disproved!

I really need a front mech specifically profiled for 22T small cogs.

I'm still getting the chain falling past the small cog on occasion.

I'm confident that if changed the 22t for a 26t the issue will resolve itself with the current setup but I'm not sure how the smaller cog difference will impact on the change to and from the middle ring.

Ian
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CREPELLO
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by CREPELLO »

Some things that will prevent a smooth gear change, especially middle to small chain ring:
*Worn front mech pivots = loose cage (especially with the top swing dwsign)
*Worn chain - becomes tooo flexible.
*Worn middle ring teeth - they could have become squashed, producing sharp edges which prevent the chain from disengaging easily (can be filed off)
*Sticky cables (and/or sticky mech and shifters. Spray liberally with WD40 and agitate to trouble shoot)
*Bad mech/chain ring compatibility, where the middle/outer difference puts the mech too high up and further away from the middle ring.
*Bottom bracket length.

There's also the issue of using whether you're using a regular 63-66 deg chainstay angle mech, or a 66-69 deg mech, sold for 'trekking' frames. I had one of those on my Galaxy once. Came to change it and bought the regular version and didn't have any gear change issues at all, although I was using friction shifting. I've never knowingly bought another trekking FD again.
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Paul Smith SRCC
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by Paul Smith SRCC »

I have a similar problem as I have used a Chainset with smaller rings than the front mech’ was designed for, nearly all road bike mech’s are designed for larger overall rings, as you can see the ’mech line does not follow the chain ring’ so the mech’ pushes the chain too far away from where the chain disengages the chainring

Image

This can and in this case does mean that you don't get such good gear change, more noticeably when changing into the smallest ring. I have got it working just good well enough, but it is definitely a compromise, I try not to change down under full pressure and if possible not when in the largest rear sprocket, I get a better shift if I am in 3-4th sprocket down as the mech' engages the chain nearer where it was designed to do, as a precaution I have also fitted an’Overshift Protector'
Paul Smith. 37 Years in the Cycle Trade
My personal cycling blog, Bike Fitter at C & N Cycles
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Sweep
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by Sweep »

I'll add my question to this thread after all.

Don't trouble yourselves too much folks though as the bike isn't with me at the moment so I can't give quick feedback on any suggestions.

It is possible that the cable is catching on a bottle mount I added to the underside of the bike but the odd thing is that that's been there a while and after a fair period of all being well the problem seems to have started recently.

The chain often won't drop to 22T small chainring (triple) when bike is being ridden (less of a problem unloaded) and I often discover this when I'm on the biggest cog (28T on a 7 speed cassette) at the back in preparation for going up a hill.

But I usually find that by moving towards the middle of the cassette I can then change down to the small chainring after all.

(then of course back up the rear cog I go quickly before all momentum is lost so that I can get up the hill).

What could all that be about?
Sweep
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CREPELLO
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by CREPELLO »

Sweep, have you experimented with letting the "L" limit screw out further - thereby bringing the mech cage further in? Although this adjustment is partially responsible for preventing the chain falling all the way off, if the cage is prevented from moving enough inwards, the change to small ring won't happen. To allow full movement of the mech cage, it's important to start any adjustment off with a slack gear cable in the resting position/small chain ring.

If you're at all concerned about the chain falling off onto the BB shell, if you don't have one already, a chain-keeper device like that linked by Paul above will fulfill this role.
howfar
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by howfar »

Can anyone give examples of using STI's and a road front mech with very small chainrings that give a very good change to the granny ring - what road front mech was used? Was it a road chainset?

The reason I ask is I'm intending to build up a Surly Long Haul Trucker using left over bits - I'm going to use the 22-32-42 Alivio chainset and know I'll need to get a new front derailler. I'll be using 7 speed STI's so need a reliable road mech. Surly spec a Sora FD-3403 for their Andel chainset.

My Randonneur has a 28-38-48 Alivio set up with 11-32 cassette and a Sora front derailler and this works very well - my original post gave me some good pointers with experimenting with various combinations of mech and chainring sizes with no resolution to the downshift problems. I don't want to buy bits that won't solve the problem.......

I'll get a 12-34 cassette when the time comes to change the existing cassette and try a 26T granny ring - thats the Randonneur sorted with bits I'm confident will give me those lower gear inches.

Why get a Long Haul Trucker? It's a available in a 62-64cm frame and I want a rough stuff tourer for canal/river side/bridleway jaunts my other bikes struggle with and make use of all those bits doing nothing in the garage.

Ian
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Sweep
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by Sweep »

CREPELLO wrote:Sweep, have you experimented with letting the "L" limit screw out further -


Thanks for the suggestion crepello but if that was the problem wouldn't it stop the chain going to the small ring pretty much all the time, not just when the chain is on the bigger cogs at the back? Also, all was well until pretty recently and I haven't touched the front mech or its adjustment in ages.

I will however have a fiddle with the bike when I'm re-united with it.

Many thanks.
Sweep
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CREPELLO
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by CREPELLO »

Sweep wrote:
CREPELLO wrote:Sweep, have you experimented with letting the "L" limit screw out further -


Thanks for the suggestion crepello but if that was the problem wouldn't it stop the chain going to the small ring pretty much all the time, not just when the chain is on the bigger cogs at the back?
By letting the L limit/stop screw out you are allowing the mech cage to move further inwards. This is partly what enables the chain to shift from middle to small ring, or rather it allows the mech cage to be correctly aligned for that particularly shift.

Also, all was well until pretty recently and I haven't touched the front mech or its adjustment in ages.

That you are having a problem with this now, at this time of year suggests that the winter weather has conspired to add muck, corrode and render any lube deficient. This really is the season of seized/sticky components and creaky sounds. You'll see numerous threads for the next couple of months or so describing such problems.

So with that in mind, I would spray some lube at the mech pivots and clean the inner/outer cables and lube. While you're at tit, a little lube aimed at the shifter wouldn't go amiss.
howfar
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Re: 28-38-48 swapped to 22-32-42 - FD shift problems

Post by howfar »

Finally sorted this issue sorted out on the Randonneur - got an XT M781 triple Dynasys FD today and this shifts under load in all combinations are slick and immediate.

Using 11-32 8 speed cassette and 22-32-42 Alivio crankset
Bar end shifters
Alivio 8 speed RD

The new FD has a profile for 42T max outer ring with a conventional swing and a 66-69 degree chainstay angle.

Just need to put a new chain and new middle chainring on to complete the service - I've shellaced the tatty Brooks Honey Bar Tape and this looks really classy now.

Haven't used the Randonneur as much over the last year - my Surly LHT has been well used as a roughstuff bike - now tempted to have the same lower gearing put on this!

Ian
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