RandomTroll

I have a triple-chainring crank, a Shimano 105, 5-bolt, 110mm for the large and middle chainrings, 74mm for the small. The small has 24 teeth; the large has 52; the middle has 36 (close to the geometric mean of 24 and 52). I use the middle most of the time.

I don't remember when it happened, but I can no longer shift from the small to the middle without shifting to the large first then down, and I have to do that carefully so as not to shift back onto the small. This has persisted over changes of chain. Is this a sign of wear in the middle chainring? It's not so worn that it doesn't work with a new chain.

I have lots of choices in styles for a new chainring: road, bmx, mtb, compact, touring. Is there a reason to choose one over the other? Will any with the correct specs not work? What makes a chainring 'compact' - is it thinner?

The 'manual' that has come with some of my chainrings instructs me to install them in a certain way. The middle chainring now installed is a bit thicker on one side than the other; according to the instructions I installed the thicker side towards the small chainring. I suspect that installing it the other way would make shifting easier. Would that make it work improperly somehow?

Some chainrings are 'outer', some 'inner'; none are 'middle'. Should I treat a middle as an inner or an outer?

Al1943

A middle is a middle, not an outer or an inner. The better middle rings have shifting assists, ramps and pins, for shifting from the inner to the middle.

FBinNY 

It's hard to mess up mounting chainrings if you just stop to think. Look at the mounting holes, and both 110bcd rings will have counterbores for the heads of the chainring bolts. So both rings are mounted with the plain side to the crank spider, and the counterbores opposite each other.

Now, there's the small possibility that your middle ring was made to be the inside of a double, vs the middle of a triple. The difference is whether it has shift ramps and gates (cut down teeth) to help the chain climb up from the smaller neighbor. The inner of a double lacks those because it doesn't have a smaller neighbor.

You can also improve shifting by "timing" your rings. Many will have a mark, which can be a stamped in diamond or triangle, or a bit of a tit on the inside. This mark is aligned either with a corresponding ark on the outer or the crank arm. Timing the rings ensures that the chain shifts from the smaller timed so the teeth can slide straight in rather than bumping against the rollers.

Take your rings off, check for timing marks, flip so the C-bores are where they belong and remount, and that should go a long way to solving the problems.

RandomTroll

I've done a lot of shopping but have yet to find a chainring identified as a middle. Every 36 I have seen has called itself an inner; would that be because everybody else uses a 36 as an inner? I've found some that claim to be 'ramped': would that fill the bill?

I take that back. I expanded my search criteria to look outside Shimano & SRAM and find some middle chainrings. One of them calls itself a middle but lacks ramps: is that a scam?

That's the way I mount them

There's a very large possibility this is the case.

The instructions mention this. I installed them with the mark in the proper place.

Chris_W

Stronglight and TA should make middle 36 tooth, 110mm BCD rings.

With a setup like yours (24/36/52), I doubt that the rings are optimized to function together, and so the timing is not necessarily optimized when you have all of the marks on the chainrings aligned. The timing is important to allow the chain to be engaged on the two chainrings at the same time during the middle of the shift. I would therefore try rotating the inner ring one step at a time to see if any of the other 4 positions provide better shifting than what you currently have.

I've not seen a 105 triple crank with 110/74 BCDs, and I'm quite obsessive about my road triple cranks. I think you may either have the BCD and middle ring size wrong (because 105 triples, even the old 1057 model, had a 130 mm outer BCD that can only take down to a 38 tooth) or the crank model wrong. You should double-check this before ordering any new chainrings.

FBinNY 

A ramped chainring would be a middle since the ramps only help to shift from the smaller neighbor. Most mtb 36t chainrings would be middles since mtb doubles aren't that common.

LesterOfPuppets

I'd guess the problem is not enough tension in FD cable. Try unscrewing the barrel adjuster at the cable stop a bit to see if you can hit the mid on the way up.

Can you take good pics of mid ring teeth profiles? One can usually visually verify worn rings.

As to replacement rings, Universal carries Dimension 110mm 36t mid rings, but $54, ouch. Could probably find a like new 105 triple crankset on eBay for that.

Couple of other notes about things mentioned:

36T small rings are common on CX cranks.


Doubles are actually fairly common on MTBs these days. XTR, XT and plain ol' Deore doubles are available.

Al1943

Here is a link to a reputable business, Peter White Cycles, that sells a lot of chainrings and offer a lot of associated information. There are 36 tooth 110 BCD middle chainrings listed. If you order here be sure you are buying Shimano compatible ring(s).
Chainrings

fietsbob

I use a 24,40,50 triple and a 26,42,52.. 16t and 10t gaps, My shifters are friction bar end . so its a hand skill,

and being practical as to when to do the big up shift, noting the terrain.

Clem von Jones

FD cable tension can be very finicky, and the shape and orientation (left-right swivel, except for a fixed mount) of the cage has as huge impact on smooth shifting, than as already mentioned above unless you have compatible Shimano Hyperglide rings they might not play well together. Hyperglide rings have sculpted teeth to facilitate smooth shifting so if you mix different manufacturer's rings it can cause problems. There are sometimes differences between 8, 9, and 10 speed chainrings, and according to Sheldon Brown the space between some of them are different. I think if you put the bike up on stand and fiddle with the cable tension a bit you'll likely solve the problem, otherwise check ring compatibility and dérailleur cage shape and orientation. Sometimes the shape of a cage will bend if the bike has fallen over, for example, and sometimes the left-right orientation of the cage isn't quite right so that it isn't exactly parallel to the rings. It's also possible that you've gone too extreme on the size range. I tried to do the same thing on my touring bike and also had a lot of difficultly shifting between rings and dropping the chain. I finally gave up and went back to normal 30-42-52 but I'm going to compensate for it by putting a greater range cassette on the back. It would be slick if a manufacturer would design a huge-range crankset for touring; there's something we need but can't buy, or perhaps TA sells one for a small fortune. I also think someone should manufacturer a mountain bike style front dérailleur that works on huge rings as a match for this theoretical touring triple. The road style cages aren't quite right for this.

Now someone will chime in about their TA crankset that works like a dream but costs $500. I bet fietsbob built his own from Sugino parts but I wonder how it would work with STI.

RandomTroll

I lowered the front derailleur 4mm and solved this problem. I don't remember raising it: could it have worn in such a way to make shifting from the small to the middle difficult?

HillRider

That was exactly my first thought, I've also never seen a 105 triple crank of any kind with a 110 mm BCD. All of them, are 130/74. The only 110 mm 105's are "compact doubles" AFAIK. If it's really a 105, I wonder if the middle chainring is a 39T.

hueyhoolihan

i think i would look at the FD's mount and from that determine whether or not it is reasonable to assume that an unfortunate combination of a loose clamping bolt (assuming it doesn't screw directly into the frame) and direction of cable pull could conspire to raise the FD. because IIRC, some pull from the bottom, some from the top, and some use a clamp and others bolt, directly or indirectly, to a fixed place on the frame.

anyway, glad to hear it's fixed. i was worried there for a while.

ThermionicScott 

Aha! If the FD is too high (Shimano's recommendation is that the outer part of the cage be 1-3mm away from the big ring when it is right over it), you can have similar problems to RDs with too much "chain gap" (jockey pulley a long ways away from the cogs) -- control isn't as good, so you need to overshift to make the shift happen.

RandomTroll

The cable pulls down.


Now you tell me.