Shimano 105 triple chain ring sizes

[beetroot]

I'm a techno ignoramous. Shimano 105 triple is supplied with 52-42-30 chainrings. is it possible to vary this? Say 50-40-28 for e.g.

[thirdcrank]

Yes.

I reduced an Ultegra to 48-38-26 with TA rings. They do say that recent changes to the design of the 105 (and possibly others?) make that 38 impossible but your example will be OK.

[cycleruk]

Shimano tech' documents say the small chainring is 74mm BCD so yes it will take a 28 or smaller ring.
What you have to be careful of is if the front derailleur will operate at that small a circle.
If the chainring is too small then the chain will catch on the lowest back edge of the derailleur.
But Shimano also say that the difference between the big and smallest ring should be 20 teeth or less?

[thirdcrank]

I just preserved the steps and lowered the front mech a tad.

[beetroot]

Thanks for replies. Looks like it's possible. I'll investigate further

[Edwards]

On my wife's bike with a 105 splined triple I fitted a 28 inner ring after reading CJ's article about the front mech capacity.
Basically it was measure the clearance in the lowest gear you want, between the chain and the bottom of the front mech. For every 2mm clearance you can go one tooth smaller.
From what I can remember 38 is the smallest that the middle ring will take.

When I costed out the 3 replacement rings it worked out cheaper to purchase a 48-38-28 crankset.

[frank9755]

Yes, but...

You can fit a smaller inner ring but the outer / middle needs to have a minimum gap of 11T

I tried 26/40/50.
- The 40 / 50 didn't work satisfactorily. The inner plate on the mech is very deep so you either have to have it too high up above the outer ring, or else it fouls the middle ring.
- The 26 works ok. Shifting down onto the 26T small ring needs a bit more care than was required to go onto the 30 which it came with. A couple of times when I have rushed the downshift I have had the chain come off. Now it is fine, but I always take it easy going into that ring.

On my frame only the extreme cross-chained gear (small / small), which I would never use, leads to the chain fouling the front mech with the 26T.

[CJ]

I'm a techno ignoramous. Shimano 105 triple is supplied with 52-42-30 chainrings. is it possible to vary this? Say 50-40-28 for e.g.

Shimano 105 triple WAS supplied with 52-42-30 before 2006 (code FC-5505). The FC-5603 which replaced it, and the current FC-5703, are 50-39-30 and (unlike new Ultegra, which you can't do a darned thing to alter) they still have the usual 130/74mm bcd. So if you're buying new, the middle and outer rings will already be near enough what you want and the inner can be swapped for the 28 you'd rather have. A 26 will almost certainly shift okay too, but 24 might cause the chain to rub on the bottom of the cage.

Next question is what model year of front mech will you be shifting that with? If it's also a pre 2006 55etc. triple mech, it'll shift best with a 10 tooth outer-middle difference, but if it's more recent 5600 or 5700 series model, it'll want the 11T difference like frank9755 says above. Notwithstanding that a current Tiagra triple mech is also supposed to work with an 11T outer-middle difference, I have found that it'll shift a 46-36-24 Stronglight triple really well, provided you get the height spot on, so the inner cage just misses the very-close-to-it middle ring. (All these rings being quite a bit smaller than manufacturer's spec, they curve away from the cage, which undoubtedly helps to avoid the problem described by frank.)

[BBh]

Hello all,
Came to know about this great & useful forum.
I have a similar issue.
I have a old road-bike with FC-5505 where the front 52-42-30 are worn out.
Now, can I install ...
1. 30 teeth Shimano FC-6703
2. 39 teeth Shimano FC-6703
3. 53 teeth Shimano FC-5700 (52 works as well but I do not know)

can I fit(assemble) these all together, if I want to replace only the 3 front-chain wheels ?
Or are there any better suggestions ?

or, am I completely wrong ?
or, am I forgetting anything here ?

Any help/support is much appreciated.
Please let me know if any other information is needed.


Many thanks in advance.
BB.

[Brucey]

….or, am I forgetting anything here ?....

the middle to big interval was 10T and now you want 14T. I think this will result in a very poor front shift, amongst other things.

I would suggest that you stick with the standard ring sizes if possible, and if you do vary them (whilst using the same FD), keep the same middle-to-big interval and don't expect it all to work perfectly if you increase the total front interval too much.

If you use 39-52 chainrings then expect it only to shift properly if you use the appropriate FD, eg as per 5600, 6600 or 7800 series.

cheers

[peetee]

My Dura-Ace 7800 triple originally had a 53-39-30 which made for a ridiculously high gear for anyone who required such a low ratio so I changed the 53 to a 48. The steps between ratios are great now but the front mech is mounted higher than recommended relative to the big ring in order to clear the middle ring. The shift to 53t is still good though.

[MartinC]

I have a FC-6503 where I've replaced the original 52-42-30 chainrings with a TA 48-38-26 set. They work fine. I deliberately chose to keep the 10 tooth big/middle difference the same but it suited me anyway. I don't think the middle/small difference matters too much but I wanted the 26 anyway.

[CJ]

Or are there any better suggestions ?

Like Brucey says, increasing the outer-middle difference will make for rubbish shifting between middle and inner, in both directions but most vitally the downshift - that you always need when it's most difficult to ease pressure on the pedals on a suddenly steepening hill! So whatever you do, don't make that any more (or less) than 10 teeth.

And don't feel you have to fit Shimano branded chainrings, where it may now be very hard to find a nice quality 42T middle that's made of alloy rather than steel. TA and Stronglight are just as good and available in more different sizes. Spa Cycles is a good mail-order source and also have their own brand rings. TA is the prestige brand, but those described as 'Zicral' by Stronglight and Spa are equivalent quality and durability. You may find the shifting is not quite as slick as Shimano rings, which have more sophisticated shifting gates and shortened teeth to help the chain derail, but those features also reduce the life of the teeth and can cause the drive to feel rough in some gears, so I actually prefer the other brands.

Brucey cautions against increasing the overall range, but I throw caution to the winds and generally fit the smallest inner I can, in this case 24T. The longer drop from middle can make the chain more liable to miss the inner and fall onto the bottom-bracket: very inconvenient . But ALL triples are somewhat liable to do that and it's SO inconvenient I always fit a Jump-Stop just in case - and with that the problem is completely solved .

NOTE: other 'chain watchers' are available, but are not as reliable as the original N-Gear Jump-Stop.