105 triple to double - chainline advice

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jr970
Posts: 11
Joined: 28 Aug 2019, 6:16pm

105 triple to double - chainline advice

Postby jr970 » 2 Aug 2020, 11:18am

For various reasons I'm converting a 105 10 speed triple setup to a compact double (see viewtopic.php?f=5&t=131772&p=1381614&hilit=double#p1381614 for my original inspiration).

I have replaced the inner and middle chainrings on the existing 105-5703 triple with TA rings (28 and 42) and a plain protector in place of the old outer, and for the moment still using the old triple FD with stops suitably adjusted to stop any attempt to shift into the old big ring.

Shifts work fine up and down, but I get some rub where the chain hits the inner face of upper chainring when on the small ring but only in the smallest 4 cogs on the back. Not a major issue is that is not a combination I'd use much and it all works fine on the 6 biggest cogs.

My question is do I need to adjust the chainline? From what I understand a triple chainset puts the middle ring at 45mm, whereas in a double the outer ring is at 46 or 47mm, so to replicate this I could put a spacer on the drive side to move it out 1mm or 2mm (assuming I can find a suitable spacer).

My alternative is to use spacers on the inner chainring to widen the spacing between the two rings - 0.5mm or 1mm should be enough.

Any advice?

My ultimate goal will be to move to a GRX400 RD with 11-36 casette and Tiagra brake lever/shifters. Currently just experimenting with the chainset to see if a triple conversion does the job.

Also does anyone know a source of 24mm spacers that could be used to tune a hollowtech chainline?

Brucey
Posts: 39862
Joined: 4 Jan 2012, 6:25pm

Re: 105 triple to double - chainline advice

Postby Brucey » 2 Aug 2020, 12:43pm

shimano use spacers with some HT-II chainsets; these can be modified to suit. Likewise HT-II cups vary in width a little so can be used to adjust chainline too.

Spacers to avoid chain rub are easy enough to implement, but what is the ideal chainline anyway? Even with the same chainset it will vary between 130mm OLN and 135mm OLN.

Well in my book the ideal chainline gives the best alignment in the most used/most heavily loaded gears, whilst allowing the other gears to be accessed without problems.

So in a touring setup it often means that offsetting the small chainring further to the left than normal is no bad thing; the bottom gear ratio is set with the expectation that you might be using this gear (or the one next to it) for hours at a time on a long climb, and keeping a good chainline in these gears is not at all bad idea.

The ideal chainline in the larger chainrings is dependant on what your most favoured sprockets are. In practice this means that the best chainline might vary from ~45mm to ~50mm on the big ring, using typical parts.

You can do some calculations: For example 135mm OLN rear hub with 9s shimano; it is 67.5mm from the centreline to the RH dropout. The sprockets are on a 4.35mm pitch and are (approximately) ~2mm thickness. So the centreline of the cassette is approximately 5x4.35 + 1 = 22.75mm inset from the dropout, call it 23mm to allow for the clearance from the chain to the dropout in top gear. So 67.5 - 23 = 44.5mm. So a 'nominally perfect' chainline for a triple on 9s/135mm is 44.5mm, but it would be 42mm on a 130mm OLN setup.

If you favour the middle (#5) sprocket on your converted setup, I wouldn't bother adjusting the chainline. A double with normal chaining spacing and a 44.5mm chainline will position the two chainrings at ~40.5mm and 48.5mm, so the big ring lines up almost perfectly with sprocket #6 on 135/9s.

cheers
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Valbrona
Posts: 2311
Joined: 7 Feb 2011, 4:49pm

Re: 105 triple to double - chainline advice

Postby Valbrona » 2 Aug 2020, 1:38pm

Using spacers to widen the gap between the two chainrings is not the way to sort this. That be a botch.

Forget calculations and measurements. If you are getting the chainrub as you explain, your bike is telling you to increase chainline a little. One or two mm should do it - work on the basis of trial and error. I am assuming here that your cransket will allow you to do it.

When your chain rubs on the inner face of the big chainring like that there is some element of danger because it is possible for the big chainring to unintentionally pick up the chain. It helps to at least be aware of this.

I hope you enjoy all that silly cross-chaining and endless front shifts on a double.
I should coco.

jr970
Posts: 11
Joined: 28 Aug 2019, 6:16pm

Re: 105 triple to double - chainline advice

Postby jr970 » 2 Aug 2020, 2:04pm

Valbrona wrote:Using spacers to widen the gap between the two chainrings is not the way to sort this. That be a botch.

Forget calculations and measurements. If you are getting the chainrub as you explain, your bike is telling you to increase chainline a little. One or two mm should do it - work on the basis of trial and error. I am assuming here that your cransket will allow you to do it.

When your chain rubs on the inner face of the big chainring like that there is some element of danger because it is possible for the big chainring to unintentionally pick up the chain. It helps to at least be aware of this.

I hope you enjoy all that silly cross-chaining and endless front shifts on a double.


Thanks for the advice - I'll scrap the idea of widening the chainring gap and try a small spacer on the drive side.The current chainline appears pretty much ideal for the 42 tooth chainring, my concern is just as you say - forgetting which combination I'm in and having the ramps pick up the chain unintentionally.

As to whether this is all worth it - well I'm not committed, this is just an experiment! In an ideal world I'd fit a trekking triple with something like 26/36/46, but in the wonderful world of 2020 Shimano that's not easy to do without going to a 50mm chainline. Life was easier with old style BB, sugino triples and bar-end shifters.

Brucey
Posts: 39862
Joined: 4 Jan 2012, 6:25pm

Re: 105 triple to double - chainline advice

Postby Brucey » 2 Aug 2020, 2:10pm

Valbrona wrote:Using spacers to widen the gap between the two chainrings is not the way to sort this. That be a botch.


nope

Forget calculations and measurements.


nope x 100

Not a single part of your bike would work if it were not for calculations and measurements.... :roll:
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jr970
Posts: 11
Joined: 28 Aug 2019, 6:16pm

Re: 105 triple to double - chainline advice

Postby jr970 » 2 Aug 2020, 2:39pm

Brucey wrote:
Valbrona wrote:Using spacers to widen the gap between the two chainrings is not the way to sort this. That be a botch.


nope


Not a single part of your bike would work if it were not for calculations and measurements.... :roll:


Thanks - so I guess not a hard and fast rule. I'll do some measurements and see what chainline(s) I'm getting for the inner and outer rings currently. Do you know what the theoretical centre to centre spacing between chainrings should be (10 speed),?

Brucey
Posts: 39862
Joined: 4 Jan 2012, 6:25pm

Re: 105 triple to double - chainline advice

Postby Brucey » 2 Aug 2020, 4:11pm

jr970 wrote:
Brucey wrote:
Valbrona wrote:Using spacers to widen the gap between the two chainrings is not the way to sort this. That be a botch.


nope


Not a single part of your bike would work if it were not for calculations and measurements.... :roll:


Thanks - so I guess not a hard and fast rule. I'll do some measurements and see what chainline(s) I'm getting for the inner and outer rings currently. Do you know what the theoretical centre to centre spacing between chainrings should be (10 speed),?


it is around 8mm but it increases (and requires shaped chainrings to stop 'riding' on the small ring) when the chainring interval increases. So it is more for 34-50 than for 39-52 (say) and the offset is built into the chainrings accordingly. With non-standard setups you often have to do a bit of fiddling to make things work.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

jr970
Posts: 11
Joined: 28 Aug 2019, 6:16pm

Re: 105 triple to double - chainline advice

Postby jr970 » 2 Aug 2020, 4:35pm

Hi

Thanks to @brucey and and @valbrona for the help and advice.

I have 135mm drop-outs and the current setup seems to put the "new" top ring (i.e. the middle of the triple as-was) at 46mm (at least as near as I can measure it) so I guess that's pretty much in line with what you would expect.

Given I'm now on a double setup I think I can afford to go out by 1 or 2mm and still maintain good chainline for the big ring (which is sized to be the one I use most of the time). I've got some 24mm ID x 1mm spacers on order so will do some experimentation when they arrived and also some 0.5mm and 1mm chain bolt washers just in case it needs a combination of both - as I'm using TA chainrings they are generic 9/10 speed, rather than tailored to a set like some shimano rings, so may need a bit of fettling to get the spacing right - it looks a bit tight at the moment but I need to get the chainset off again to measure properly.

Thanks for the help..... when I get it working I'll post the solution in case anyone else has the same issue.

jr970
Posts: 11
Joined: 28 Aug 2019, 6:16pm

Re: 105 triple to double - chainline advice

Postby jr970 » 6 Aug 2020, 4:03pm

After a mix of measurements and trial and error I settled on the following:

    1mm x 24mm ID spacer (Wheels Manufacturing, sourced on Amazon) on the crankset to move the drive side chainline out.
    0.5mm x 8mm shim washer inside the smaller ring to increase the chainring to chainring spacing - I suspect needed as TA chainrings may have a slightly different offset to the shimano originals.

I now get no unintended chain pickup and 8/10 gears are working on the smaller ring with no chain-rub (although you would not want to use that many as I've deliberately set the small ring chainline to optimise the lowest 3 gears. Bigger chainwheel works fine across the range and chainline matches the middle cogs which is what I use most.

On the "triple vs sub-compact double" front the jury is out! One ride shows that on rolling flat-ish country it works fine, I can stick in the 42 tooth outer ring for 90% of the ride, so the number of "1 down, 2 up" changes is limited. Yes top speed is limited but given my age, fitness and riding style if I need more than 42x11 I'm freewheeling down hill anyway! A few more rides on more hilly terrain will see.......

Assuming all goes to plan then winter will see a move to 11-36 cassette, GRX-400 RD and Tiagra levers/FD which completes the conversion to gravel bike setup......

Thanks guys for the help and advice....