Going from dual to triple crankset

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skylined
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Joined: 27 Dec 2020, 1:33am

Re: Going from dual to triple crankset

Post by skylined »

531colin wrote: 8 Aug 2022, 10:19am from the picture it looks to me like the chainstay cranks out immediately behind the existing 36T chainring.
Are you certain it doesn't?
Forgot to mention I will be buying the 2021 version of the same bike instead, identical specs, just different color. So regarding your observation you can see the clearance at 2:01 , 2:25 , 2:37 and 4:32 of this YT video, so it does look like the sales person (I dislike sales people but that's a different story) is right.
slowster
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Re: Going from dual to triple crankset

Post by slowster »

skylined wrote: 7 Aug 2022, 6:59pm maybe a wider bottom bracket to clear the chainstay
Not an option with Hollowtech II chainsets.

The fitted chainset is Boost standard with a 53mm chainline. Boost was introduced to allow chainstays to be widened to accommodate wider tyres by increasing the chainline and using only 1x or 2x chainsets. Triple chainsets are all non-Boost, and the inner ring in particular may be very likely to foul on the chainstay of a frame designed around the Boost standard. Even if the chainset can be fitted, the different designed front and rear chainlines may affect shifting performance.
skylined
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Re: Going from dual to triple crankset

Post by skylined »

slowster wrote: 8 Aug 2022, 12:02pm Not an option with Hollowtech II chainsets.

The fitted chainset is Boost standard with a 53mm chainline. Boost was introduced to allow chainstays to be widened to accommodate wider tyres by increasing the chainline and using only 1x or 2x chainsets. Triple chainsets are all non-Boost, and the inner ring in particular may be very likely to foul on the chainstay of a frame designed around the Boost standard. Even if the chainset can be fitted, the different designed front and rear chainlines may affect shifting performance.
Thanks for the reply. The new chainset I'm looking at (FC-T6010) is also Hollowtech II and the Q factor is +3mm (so maybe half of that on the drive side) and chainline +1.2mm which is a small difference so I don't know what effect that would have on shifting, probably not noticeable?
Regarding the inner ring touching on the boost frame issue, looking at Sehlon Brown's page there is an image that shows how the chainline is defined on a double and on a triple crankset. If that image is correct, the +1.2mm (i.e. bigger) chainline difference means the smaller chainring may just about fit in there? If the standard space between chainrings is 5mm (is that true?) then the smaller chainring will sit 1.3mm inwards on the new triple crank compared to the original (5mm halved, minus1.2mm)
slowster
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Re: Going from dual to triple crankset

Post by slowster »

I was mistaken about the fitted chainset being Boost standard (it is only the 1x version of FC-5100 that has a 52mm chainline, and as you note the chainline of the double is 48.8mm).

I *think* the chainring spacing could be more than 5mm, possibly nearer 8mm. If so, the 36t middle and 26t inner rings of the triple could be up to 3mm further inboard than the 36t outer and 26t inner rings respectively of the fitted double chainset*.

* 48.8mm chainline of the double chainset + 8mm/2 = ~53mm (vs. the 50mm chainline of the triple)
skylined
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Joined: 27 Dec 2020, 1:33am

Re: Going from dual to triple crankset

Post by skylined »

slowster wrote: 8 Aug 2022, 3:19pm..
So between ~3mm and ~1mm. 1mm is unlikely to cause an issue, 3mm might or might not. I will measure my current bike and post my findings.
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531colin
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Re: Going from dual to triple crankset

Post by 531colin »

FC T6010 https://bike.shimano.com/en-US/product/ ... T6010.html
....chainline is 50mm according to that....
ie middle ring 50mm from frame centreline.

FCM 5100 -2 https://bike.shimano.com/en-US/product/ ... 100-2.html....apparently for frames with 135, 142,OLN..
48.8mm chainline... from centre of gap between rings to frame centre

FCM 5100 B2...https://bike.shimano.com/en-US/product/ ... 00-B2.html....148 OLN
....chainline 51.8mm.....as above....frame centre to centre of gap between rings.

i need to lie down now!
skylined
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Joined: 27 Dec 2020, 1:33am

Re: Going from dual to triple crankset

Post by skylined »

I am now in possession of the bike and as you can see here there is plenty of clearance for the FC-T6010 crankset , I believe the inner chainring will move about 2mm inwards.

I have a question about the new front derailleur. The current deraileur is clamp on, high clamp/bottom swing, bottom pull, so I thought the new one should have the exact same specifications and this deraileur seems to tick all the boxes. Can you verify it will fit? I believe it is dual pull compatible. Many thanks
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531colin
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Re: Going from dual to triple crankset

Post by 531colin »

Specifications are here....https://bike.shimano.com/en-US/product/ ... 0-H-3.html

Mostly these need to agree with the chainset specifications**; the exception is "chainstay angle" which is a frame dimension

** number of chainrings....3....check
Chainline ....I think 50mm both?
tooth numbers of rings .....difference big ring to middle ring is important.
Number of "speeds"....both 10 I think?
skylined
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Re: Going from dual to triple crankset

Post by skylined »

531colin wrote: 19 Aug 2022, 4:01pm tooth numbers of rings .....difference big ring to middle ring is important.
Number of "speeds"....both 10 I think?
Yes, 10, top-mid tooth difference is 12T, also check. The only issue is here, the current distance between the derailleur and the bottle mount is 29mm (not 2.9mm) so not sure if I should get high clamp or low clamp aka bottom swing or top swing, the FD-T8000 comes in both versions. The high clamp may sit just above the bottle mount which would be fine, or maybe not?
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531colin
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Re: Going from dual to triple crankset

Post by 531colin »

46T chainring is about 195mm diameter....that might help your decision if you make some assumptions about the dimensions of the potential new front mech.
The low clamp mechs. don't seem to last as well as the traditional ones before the pivots go sloppy.
If you buy stuff on line, most people seem OK to take it back if it doesn't suit, always provided it looks new.
Matt.P
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Joined: 29 Mar 2024, 8:44am

Re: Going from dual to triple crankset

Post by Matt.P »

How did you get on with this conversation? I have the same bike and want to do the same as you, also noticed your thinking of changing your wheels ? If so I might be interested in buying your originals as spares if your going to part with them.
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