Triple to double - old-ish Shimano

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nickp
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Joined: 9 Oct 2007, 11:12am

Triple to double - old-ish Shimano

Postby nickp » 29 Jul 2020, 12:20pm

I wonder if I could beg some more help for my Synapse upgrade project?

The new (to me) 2016 alloy frame is now up and running pretty sweetly with this setup:
Shifters: STR700 (not 6500 as per my previous post!)
Front Derailleur: FD5603
Crank: SC5603 50-39-30
Rear Derailleur: RD5600 12-27 10 speed
Front Brake: 451 for the reach
Back Brake: 5600

However, of all things, a terminally bent B screw (currently eating its way through the hanger) is bringing forward the next stage of the project: the move from triple to double. Of course, I would like to change as little as I can possibly get away with but in the end I would like to have 50-34 on the front and 11-32 10-speed at the back, or something very similar. I have ordered an RD 5701 GS (and a new hanger) which would then have the required capacity once I have a double up front. But what to do at the front? I'm struggling to find compatibility information for the STR700 shifters. There is some in the usual Shimano places but it doesn't appear to be as complete as for the 5600/5700 class kit.

My preference would be install FC5750 50-34 and cross my fingers that it could be made to work with the FD5603 / STR700 combination.

I understand the STR700 can be configured to work with doubles or triples, but equally I read the 5750 crank has the chainrings 1mm further apart than the 5600, and I'm unsure how critical that could be. Feels like a rounding error ... I wouldn't object to replacing the front derailleur, but, as ever, any more than that probably means getting spendy.

Am I barking up the wrong tree with this or am I overthinking things and this is just all going to work because Shimano?

Thanks again!
Nick

Edited for completeness to correct the new rear derailleur - 5701 not 5750!
Last edited by nickp on 30 Jul 2020, 8:36am, edited 1 time in total.

Brucey
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Re: Triple to double - old-ish Shimano

Postby Brucey » 29 Jul 2020, 9:52pm

details of ST-R700 compatibility are given in the 2008-2009 compatibility chart in the shimano archives

https://productinfo.shimano.com/#/archive

if you want to 'change as little as possible' then my suggestion would be to leave well alone, stick with the triple. IME very many riders end up cross-chaining much of the time when they use a compact double, so worth checking this before you take the plunge, especially given that you will probably have to change more parts than you expect before you get it working properly.

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

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nickp
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Joined: 9 Oct 2007, 11:12am

Re: Triple to double - old-ish Shimano

Postby nickp » 30 Jul 2020, 8:35am

Thanks Brucey, that archive index is really useful. Eminently sensible advice too - keeping the triple does make it a more flexible proposition, and since it all works just now, why disrupt it all?

cheers
Nick

Jamesh
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Joined: 2 Jan 2017, 5:56pm

Re: Triple to double - old-ish Shimano

Postby Jamesh » 30 Jul 2020, 8:57am

The jump down from 50 to 34 is a bit annoying tbh.

A triple leaves you in better gears most if the time.

Cheers James

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Triple to double - old-ish Shimano

Postby Brucey » 30 Jul 2020, 9:00am

that's pretty much how I look at it. If you try and convert to a compact double using those shifters I expect you will find that the indexed FD will turn out awkward, with trim clicks in the wrong place etc. Often there are workarounds, but at best you are going to save what, about 100g tops?

Indexed front shifting is -IME- barely tolerable on road bikes even when everything is matched perfectly. If you are happy with the FD setup/function as it is, messing about with it wouldn't be my first choice.

cheers
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garygkn
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Re: Triple to double - old-ish Shimano

Postby garygkn » 30 Jul 2020, 6:15pm

Personally I would always opt for a triple if there's a choice.
The gearing on a triple is much less compromised to my mind.
I can't see any advantage myself to a compact drive over a triple.
The triple for my money has the best of three worlds.
The compact feels like a compromise of just two worlds already mentioned is the compromised jump on the two rings.
The other advantage to a triple is that it can be set up with close gearing.

Brucey
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Re: Triple to double - old-ish Shimano

Postby Brucey » 30 Jul 2020, 8:05pm

gearing is a very personal thing of course but with the extant triple setup (and my current state of fitness....ahem) I wouldn't get much use out of the big ring, unless I was being dragged along in a fast-ish group, going faster than I'd manage by myself.

Compact double 50-34 / 10s 11-32 is compared with triple 50-39-30 / 10s 12-27 here;

http://ritzelrechner.de/?GR=DERS&KB=34,50&RZ=11,12,14,16,18,20,22,25,28,32&UF=2150&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=30,39,50&RZ2=12,13,14,15,16,17,19,21,24,27&UF2=2150

and the 50T chainring does look more useful with the compact double. But that is due to the cassette change; The compact double is compared with the triple (using the same 11-32 cassette) here

http://ritzelrechner.de/?GR=DERS&KB=34,50&RZ=11,12,14,16,18,20,22,25,28,32&UF=2150&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=30,39,50&RZ2=11,12,14,16,18,20,22,25,28,32&UF2=2150

This looks like a much better set of gears for many types of riding using the triple, with smaller double-shifts, and I'd be using the big ring on the flat whenever the conditions were not unfavourable. The middle ring would get a lot of use on draggy climbs and into headwinds etc.

Also I note that using that cassette the 11T (as is so often the case) is pretty much redundant. I'd sooner have an extra sprocket somewhere else, or remove it completely and have a stronger, less dished rear wheel.

cheers
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nickp
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Re: Triple to double - old-ish Shimano

Postby nickp » 30 Jul 2020, 9:04pm

Those charts are very interesting - not seen them before. Just the analysis I need.

[quote]This looks like a much better set of gears for many types of riding using the triple, with smaller double-shifts, and I'd be using the big ring on the flat whenever the conditions were not unfavourable. The middle ring would get a lot of use on draggy climbs and into headwinds etc.[/quote]

and this sounds just like me.

In nice conditions (flat, no wind) I tend to use a 75 to 85 inch gear and try for a cadence of about 80. On that basis the double has maybe 1-2 usable gears one per big ring while the triple has several more, spread more evenly across the 50 and 39 rings. That makes a pretty conclusive case for the triple for my type of riding, even with the 12-27. If I want some lower gears I can always replace the cassette with the 11-32 on the triple (just, with a little jigerypokery). I might even have used that 11 last weekend, running downwind across the Borders.

And now I've got the new rear derailleur and a straight hanger on the frame and removed the spacer that made the old bent hanger work with the bent B screw, everything's running very nicely thank you. Even the much maligned front indexing and trimming is acceptable! So the triple stays for now anyway.

cheers
Nick

Brucey
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Re: Triple to double - old-ish Shimano

Postby Brucey » 30 Jul 2020, 9:08pm

the large cassette with the triple setup will most likely leave you with the chain running slack in small-small gear combinations. But this is not the end of the world, you won't be using those anyway....?

cheers
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nickp
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Joined: 9 Oct 2007, 11:12am

Re: Triple to double - old-ish Shimano

Postby nickp » 30 Jul 2020, 9:40pm

Yes the chain's already too slack for my liking in the small-small so rationing the use of the small chainring is no big deal.
cheers

iandusud
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Re: Triple to double - old-ish Shimano

Postby iandusud » 31 Jul 2020, 5:44am

All good advice. Stick with the triple for all the reasons stated.