Smaller Chainrings with Shimano FD

[meic]

I tried to get a better chainline for the lower gears where I spend most of my time.

There are things to thwart you.
Most extreme is the front deraileur starts hitting the frame.
If it doesnt hit the frame it may just not go over far enough and even though gears change in the workshop, it will not shift off the middle ring to fall on the inner when pedaling hard uphill, the chain just weaves around the derailleur.
Or the inner chainring can get too close to the frame.

[NetworkMan]

I tried to get a better chainline for the lower gears where I spend most of my time.

There are things to thwart you.
Most extreme is the front deraileur starts hitting the frame.
If it doesnt hit the frame it may just not go over far enough and even though gears change in the workshop, it will not shift off the middle ring to fall on the inner when pedaling hard uphill, the chain just weaves around the derailleur.
Or the inner chainring can get too close to the frame.

Perhaps this is a summary?
If you are using a road FD and STI the safest thing to do is to stick to the recommended axle and a road chainset with rings close in size to those intended for the FD. If you are using a 135 mm dropout wheel then you get a small (2.5 mm) bias in favour of the low gears which is probably no bad thing if you are using the stronger wheel. Only a small adjustment to the FD low and high limit screws will be needed for this wheel.
If you are using bar-end or down-tube shifters then there is more freedom to use some, or all of, smaller rings, a mountain bike FD, a mountain bike chainset, a shorter BB axle to get more low gear bias.

[Sweep]

If it doesnt hit the frame it may just not go over far enough and even though gears change in the workshop, it will not shift off the middle ring to fall on the inner when pedaling hard uphill, the chain just weaves around the derailleur.
.

Can you explain why this is to someone not that technical? I have a bit of bit of a problem sometimes on a self built bike. Changes all fine and dandy on the stand, between sometimes and quite often refuses to drop to the bottom ring if actually going uphill! My solution at the mo is to change down before the hill. Sometimes pedalling extra fast before the downshift seems to help as well though I must admit to not really understanding why that is either.

[Brucey]

middle to inner changes are notoriously iffy on road triples, especially if there is any mismatch whatsoever in the parts used; however to make the shift work (well enough) often all that is required is to back off the pedals for half a turn.

BTW it often makes most sense to shift onto the small ring when you are in the third largest sprocket on the middle ring; the shift will go less well if you are already in middle-1 (big) (because the chain will be at a less favourable angle for the FD to be able to push it) and there is still room to do a double-shift so that (say) you can be using small-5 after the double-shift.

You might be thinking that the middle to inner shift works OK on your MTB; well a lot of effort went into making this so. The chainrings are invariably heavily manipulated, the middle to inner interval is not too ambitious and (although they are not great from other points of view) top swing FDs allow a slightly better geometry because the cage gets noticeably lower as it swings inwards.


Some things that turn front down- shifting bad on triples;

- wrong FD for the chainring intervals
- big interval between the middle and big rings (normally ruins the middle to inner shift)
- aftermarket chainrings that don't have such well formed gates
- aftermarket chainring in the middle position that is really meant as the inner ring on a double
- trying to shift under load
- using the wrong chainrings for the chain (eg 9s chain on 8s chainrings)
- chain type (quite small changes in sideplate camber shape can change the shifting quite a lot)
- chain wear; once the chain is worn it may be laterally flexible enough that it doesn't want to derail off the middle ring. Again a new/different chain may fix this.

Because you are usually climbing when trying to do the middle-inner shift, any flaws in this shift are especially frustrating; by contrast the other shifts are usually acceptable if they are a bit slow or they force you to back off for a couple of seconds whilst the shift is made.

For an easy life with a road triple there are two fairly surefire routes

1) use a complete matched set of good parts from a single manufacturer
2) set up your bike with chainrings that look more like a half step plus granny arrangement.

If you can't do any of the above you may find that you get an appreciable benefit (in combination with an FD that suits the middle-outer interval perfectly) by simply reducing the middle-outer chainring interval slightly. Even 2T can make a noticable difference here.

Note also that if the middle chainring is smaller than the average of the other two, you may also experience poor shifting going inner to middle; you can end up shifting inner to outer in some cases, often enough to be annoying.

cheers

[meic]

If you are using bar-end or down-tube shifters then there is more freedom to use some, or all of, smaller rings, a mountain bike FD, a mountain bike chainset, a shorter BB axle to get more low gear bias.

The issues that I am mentioning are totally independent of which sort of shifter you are using, it is the absolute limits of the frame or the front derailleur itself.

Sweep, the reason why it works in the workshop but not on the hills is because the chain is under tension which keeps it in place on the chainrings. When I had such a set-up I found that a newer stiffer chain would work when a part worn one would not, the older one having more sideways flex allowing it to snake around the derailleur more easily.

[The utility cyclist]

I run 50/39/24 Miche Hollowtech II with Ultegra 6703 FD, works brilliantly and no issues going middle to inner nor any need to back off. I'll eventually get a 36t middle but it might take a few years to do so.
The 6700 series triple is easily on a par with 7803 in shifting terms.

[NetworkMan]

I've got my new TD2 cranks with 48/38/28 fitted and adjusted so they are ready for a road test. At first I fitted the FD so that it was a minimum of about 1 mm above the big ring; Shimano say 1-3 mm. That meant that when shifting from 38T to 48T the chain was caught between the big ring and the upper inside edge of the cage (the cage becomes narrower in this region) before it had climbed onto the big ring. I raised the FD by about 2-3 mm and this fixed the problem. I've not tried changing in all the crazy combinations, middle ring biggest sprocket to big ring, for example but in all the ones I have tried it seems to change OK.
I'm lucky in that the bolt heads holding on the little ring only just clear the pointed end of the lug on the BB shell - probably due to the chunky chain stays Dawes have used.
If running middle ring to big sprocket (perhaps not advisable anyway) the chain rubs the cage but a touch on the black lever trims the cage inwards a smidgin and stops this. A trim in the other direction is needed if running little ring to small end of the cassette - again probably not a good idea.
Gearing seems just about right for me now: 36 to 84 inches with the 38T ring on the 7 middle sprockets of the 9 speed 11-32 cassette - the 11T top sprocket is still too small but nothings perfect!

A perhaps fairly obvious tip:- Because the FD was already fitted I didn't have Shimano's "pro-set" tool to help setup the FD. I found that a 1/4" drive socket of the right size was fine for this - just choose one that moves the outside edge of the FD out so it is just above the big ring.

[NetworkMan]

If you are using bar-end or down-tube shifters then there is more freedom to use some, or all of, smaller rings, a mountain bike FD, a mountain bike chainset, a shorter BB axle to get more low gear bias.

The issues that I am mentioning are totally independent of which sort of shifter you are using, it is the absolute limits of the frame or the front derailleur itself.

I'm just highlighting the fact that with STI levers you are pretty much forced to use a road FD not a mountain bike one. Also with bar-end or downtube levers you can overshift if needed. With a mountain bike FD on a road frame you may be able to get extra capacity due to the different chainstay angle (assuming that the bottom of the cage doesn't hit the chainstay).

[NetworkMan]

Just to say thanks for all the help sorting out the rings and the FD. Seems to change fine now and bike rebuild is now more or less done with new compact bars and longer stem, correct width guards, Schwalbe One Evo tyres and Spa TD2 chainset. Mountain bike transmission on the rear was done already. Rides quite nicely now though the rear wheel seems to have accquired a tinkling sound perhaps due to the rather slack spokes on the original old wheel. Before and after pictures enclosed:-