Do I need to change my front derailleur if I switch to smaller chainrings ?

[Tangent]

Hello Everyone,

I'm looking for some advice regarding a campagnolo comp triple front derailleur and chainrings.

Currently my partners bike is equipped with a campagnolo comp triple (53/42/30) running a 13-29 cassette on the back.

The lowest gear this offers is about 28" which she feels is too high and would prefer a lower gear of around 22 or 24".

As we are already using the largest cassette, we are considering switching the chainrings to either a 48/36/26 which would give a 24" bottom gear or 46/36/24 giving a 22" gear.

If we were to go ahead with either of these chainring combinations would it be necessary to change the front deraileur also?

Thanks

[Biggsy]

You won't have to change the front derailleur, but one designed for smaller rings may work better with the 46/36/24 combination if you opt for that.  However a derailleur of a different make may not be so compatible with the Ergo shifter if it's one of the new ones with more chunky indexing than the micro indexing of the older ones.  I'm not sure about that point.

Anyway, I would certainly suggest trying your existing derailleur first.

I'm currently using a Campagnolo Daytona Triple front derailleur (probably very similar to the Comp) with 50/39/24 rings and an old-style Mirage Ergo.  Setting it up was tricky and I offset the inner ring further inwards with washers to improve shifting to the inner ring.  But once it's done, it's done, and it works well enough.

[CommuteTooFar]

I use a Campy Athena Racing T front derailleur.  Originally I had 46 36 24 chainrings.  I migrated to 48 38 26.  Two points the derailleur works fine on smallish chainrings. When I started using the 48 tooth ring I needed to raise the derailleur a little higher.

You will need to move the derailleyr down.  It will work.

[Biggsy]

By the way, you could consider 48/36/24 and many other combinations too besides the two mentioned.  Replacement rings of various sizes are available for nearly all good cranks from Stronglight and TA, and front and rear derailleurs can in reality be made to cope with wider gear ranges than the manufacturers say.

[tatanab]

we are considering switching the chainrings to either a 48/36/26 which would give a 24" bottom gear or 46/36/24 giving a 22" gear.

The Campag triple will not do that.  The smallest middle ring is 39T.  You can change the 30 to 24/26 ok because the chainrings are the same PCD as mountain bike chainrings.

I use 50/40/24 with a cassette of 15-28 and use a standard Centaur (maybe Veloce, I don't remember) triple changer with no problems.

[citoyen]

Anyway, I would certainly suggest trying your existing derailleur first.

Second this.

I made a similar adjustment to my wife's bike and didn't change the front mech until I discovered I had to. But it's got to be worth trying the existing front mech first before recklessly splashing out on a new one. Unless you are made of money.

d.

[Biggsy]

we are considering switching the chainrings to either a 48/36/26 which would give a 24" bottom gear or 46/36/24 giving a 22" gear.

The Campag triple will not do that.  The smallest middle ring is 39T.

That is correct, though the whole chainset could be changed.  Perhaps that's what Tangent is considering.

You can change the 30 to 24/26 ok because the chainrings are the same PCD as mountain bike chainrings.

Yes, 74mm.

[Tangent]

Wow!

Thanks for all the good information everyone.

My original intention was to only change the individual rings and not the whole chainset.

It never occurred to me that there would be a limit on the size of the middle ring of 39T.

I'm not sure about the merits of 46/39/24 chain rings though. 46 and 39 look awfully close to me. 48/39/26 would probably be OK.

If we decide to go with a 24T inner ring then a new chainset to get a better spread of gears from the outer and middle rings may be the preferred option. Would that be sensible?

Thanks again.

[Biggsy]

A new chainset would enable a more reasonable difference between a 24t inner and the middle ring, but there's no need for a new chainset otherwise.

Personally, I find a 39t middle ideal for cruising speeds and moderate hill climbing (with 13-29 and 14-30 cassettes), which is what I need for most of the time, so I stick with this despite it not being an ideal neighbour to the inner ring.

I recommend trying 26/39/50 first of all, then perhaps consider a new touring chainset with something like 24/36/48 if the bottom gear is still not low enough.  I can't really recommend the 24/39/50 I have (on one bike) because of the very tricky setting up and awkward shifting to and from the inner.

[Edit in purple]

[David Martin]

Smaller chainrings can make good use of a smaller chainring specific front mech. I used a Mirage CT (compact) front  mech and this ran much better on a 50/34 setup than a full size front mech.

..d

[Tangent]

Thanks for that piece of information David.

I've checked the bike and the shifters are of the older friction type and not the newer QS version so that ought to give me some scope with derailleurs if I need to.

I think I'll try the existing derailleur first and change some of the chainrings before splashing out on a new chainset and/or derailleur.

A big thank-you to everyone for all of your advice todate!

[Really Ancien]

Don't forget that the Campag bottom bracket is a different taper to others, so if you change the chainset to another manufacturer you'd need to change the chainset bottom bracket*.

Damon.

* Correction by Mod

[Tangent]

Thanks for pointing that out. I'm off to investigate further.

[David Martin]

Don't forget that the Campag bottom bracket is a different taper to others, so if you change the chainset to another manufacturer you'd need to change the chainset bottom bracket*.

Damon.

* Correction by Mod

That is correct. You can quite happily(^) run campag on shimano or shimano on campag  when chainsets and square taper BBs are concerned. Works as well as having them on the matching part, just the axle lengths will be a bit off.


^ for small values of happily as constrained by having square taper in the first place.

[Dunc]

One other thing to consider is the risk of dropping the chain off the inside when changing middle to small rings with a big tooth gap.
We changed my partner's (Shimano 105 triple chainset & FD) to 24-38-48 and the chain frequently "over shot" the 24 when changing down from the 38, despite taking great pains to align the derailure and set the inner stops.
Application of a Deda Dog Fang has eliminated the problem and I'd highly recommend this.

[Biggsy]

Yes I also had the problem of the chain overshooting the inner ring.  Offsetting has helped, as well as a Dog Fang.