Compact double chainset with square taper and 46T chainring?

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OnYourRight
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Compact double chainset with square taper and 46T chainring?

Postby OnYourRight » 4 Jul 2013, 8:34pm

I have a 2012 Dawes Clubman which pleases me in many ways but is over-geared in the best road-bike tradition.

The current chainset is an FSA Tempo triple with 30T/42T/52T chainrings (not 30T/39T/50T as Dawes advertise). The cassette is an 8-speed Shimano HG50 12–25T with 12T, 13T, 15T, 17T, 19T, 21T, 23T, and 25T cogs. The bike has a Shimano FD-2303 front derailleur, RD-2300 rear derailleur, and ST-2303 shifters.

I weigh about 65 kg (145 lb) and climbing has always been my strongest point (not saying much, mind you!). So I’m thinking of converting to a simple compact-double chainset.

The Shimano FC-2350 is an obvious candidate: compatible, cheap, and cheerful. Heavy, certainly, but I’m no racer. However, it comes with 34T and 50T chainrings. I’d prefer something around 46T for the big ring, to optimise the cruising chainline. The 34T small ring is fine.

There is a forthcoming FC-2450 chainset (from the new 2400/Claris groupset) which looks interesting, in that it will be available in a 34T/46T version. But it uses an Octalink bottom bracket. I’d prefer to stick with square taper.

Question: could I buy the existing FC-2350 chainset and a 46T chainring for the forthcoming FC-2450 (PDF), and bolt them together even though this Shimano tech doc (PDF) doesn’t mention the possibility?

Alternatively, how close can I get to a chainset with these characteristics:
  • ~34T and ~46T chainrings
  • works with my current FD-2303 front derailleur or another cheap one
  • works with an indexed ST-2300 front shifter (hoping to find a cheap left shifter somewhere)
  • square taper
  • 170 mm crank length
  • perfectly compatible with an 8-speed chain
  • durability more important than weight
  • cheap!
This isn’t a pressing thing, but I’d like to do it sooner rather than later. Once done, it’ll stay that way for a long time. I’m not the type who “upgrades” things every year.

Thanks!

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cycleruk
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Re: Compact double chainset with square taper and 46T chainr

Postby cycleruk » 4 Jul 2013, 9:00pm

How cheap is cheap?
Spa has these with various chainrings.
http://www.spacycles.co.uk/products.php ... 0s109p2799
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It's either a headwind, or you're going well.
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OnYourRight
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Re: Compact double chainset with square taper and 46T chainr

Postby OnYourRight » 4 Jul 2013, 10:35pm

£60 is a good bit more than the very cheap Shimano FC-2350, but it’s not outside the bounds of possibility.

However, wouldn’t that be a 9/10-speed chainset? I’d like everything to be perfectly compatible with my 8-speed drivetrain if possible.

I like the look of that Stronglight though.

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cycleruk
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Re: Compact double chainset with square taper and 46T chainr

Postby cycleruk » 4 Jul 2013, 10:58pm

I don't know if it's 8/9/10 speed compatable. A call to Spa would confirm.
Here's a cheaper version:-
http://www.spacycles.co.uk/products.php ... 2b0s109p45

Another possible option would be to ditch one of the rings on you current triple and alter the others but the cost may be the same as a new chainset?
There's no such thing as a tailwind.
It's either a headwind, or you're going well.
https://www.youtube.com/watch?v=81gfs4sd76E

reohn2
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Re: Compact double chainset with square taper and 46T chainr

Postby reohn2 » 4 Jul 2013, 11:09pm

Stronglight Impact is 8sp compatible and is an excellent choice :)
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niggle
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Re: Compact double chainset with square taper and 46T chainr

Postby niggle » 5 Jul 2013, 12:23am

Why go through all the hassle to convert to a double, could you not just fit a smaller touring triple?
Eg: http://www.spacycles.co.uk/products.php ... 0s109p2000

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andrew_s
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Re: Compact double chainset with square taper and 46T chainr

Postby andrew_s » 5 Jul 2013, 12:43am

niggle wrote:Why go through all the hassle to convert to a double, could you not just fit a smaller touring triple?
Eg: http://www.spacycles.co.uk/products.php ... 0s109p2000

Agreed.
If you fit a 46/34 compact double, it means that if you later decide the bottom gear isn't low enough it's new chainset time (to say nothing of the cost of changing shifters again).

OnYourRight
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Re: Compact double chainset with square taper and 46T chainr

Postby OnYourRight » 5 Jul 2013, 1:21am

reohn2 wrote:Stronglight Impact is 8sp compatible and is an excellent choice :)

It worries me slightly that the Stronglight website says the Impact is for 9/10-speed chains, here and here.

I don’t know what that means, though. Maybe 8-speed chains work perfectly on 9/10-speed chainrings, or maybe they work pretty well but are more likely to rub. I’d really like everything to be perfectly compatible. Are the teeth the same width? You’d think Shimano would have a beautifully clear website explaining all of this and the reasons behind their constant creation of incompatible standards, but no.

niggle wrote:Why go through all the hassle to convert to a double, could you not just fit a smaller touring triple?
Eg: http://www.spacycles.co.uk/products.php ... 0s109p2000

It doesn’t seem like a huge hassle from where I’m sitting. I’d need a new shifter and derailleur to keep everything neat and tidy, but I was surprised to see Shimano officially supports (PDF) using my triple shifter and triple derailleur with the compact double FC-2350 chainset.

And I’d need a new chainset (or at least chainrings) whether I go double or keep the triple.

That Spa Cycles touring triple chainset is extraordinarily cheap, though, and a good 300 grams lighter than my FSA Tempo.

Getting the 28T/38T/48T chainrings to work with a road derailleur might be a job, though. My current derailleur wouldn’t work, according to Shimano (maybe they’re too pessimistic here?).

andrew_s wrote:If you fit a 46/34 compact double, it means that if you later decide the bottom gear isn't low enough it's new chainset time (to say nothing of the cost of changing shifters again).

True. On the other hand, I’m fairly sure 34T would be fine. My old bike had a 39T inner ring and I managed. I don’t plan to tour with more than 10 kg of gear, and the bike will more often be loaded with only a water bottle. I’m also a long way from the Alps.

Thanks for the ideas, everyone. I’ll puzzle about it some more.

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531colin
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Re: Compact double chainset with square taper and 46T chainr

Postby 531colin » 5 Jul 2013, 6:38am

You are worrying far too much. Look at the standard spec. of Spas own tourer here...http://www.spacycles.co.uk/products.php?plid=m1b17s21p2554
Road 9 speed STIs, therefore road F. mech. 28/38/48 XD2 (ie Stronglight Impact, its the same), it all works happily with Spas own 4 bolt 22-up chainset, too.
I have Impact chainsets on two 8 speed bikes

niggle
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Re: Compact double chainset with square taper and 46T chainr

Postby niggle » 5 Jul 2013, 7:50am

OnYourRight wrote:I was surprised to see Shimano officially supports (PDF) using my triple shifter and triple derailleur with the compact double FC-2350 chainset.

If that is how you read it then they also officially support using the ST-2300 double STI with a triple chainset :? I think I have heard of problems reported with broken shifters, or at least indexing issues due to the trim clicks on a left hand triple STI when using it with a double chainset.


OnYourRight wrote:That Spa Cycles touring triple chainset is extraordinarily cheap, though, and a good 300 grams lighter than my FSA Tempo.

Getting the 28T/38T/48T chainrings to work with a road derailleur might be a job, though. My current derailleur wouldn’t work, according to Shimano (maybe they’re too pessimistic here?).

Yes they are too pessimistic, plenty of touring bikes going around with 48T big ring and a road mech.

OnYourRight wrote:On the other hand, I’m fairly sure 34T would be fine. My old bike had a 39T inner ring and I managed. I don’t plan to tour with more than 10 kg of gear, and the bike will more often be loaded with only a water bottle. I’m also a long way from the Alps.

Maybe not going to the Alps this year.... but why limit yourself unnecessarily? For me a 28-38-48T with a 12-25T cassette would not have low enough gears for a tourer, even if I was only going to carry up to 10Kg. My current audax/road bike has a triple with 28-39-50T chainset and 12-27T 9 speed cassette and I use all gears regularly other than the top ratio. I am building a touring bike and planning to use 22-32-42T chainset and 11-32T cassette, though I do intend to camp and carry a fair bit more than 10Kg and to head for the hills on a regular basis.

Ayesha
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Re: Compact double chainset with square taper and 46T chainr

Postby Ayesha » 5 Jul 2013, 9:11am

Some advice about setting up small chainsets.

1/ Make sure the highest gear feels laboured when riding along the flat through calm air at your cruising speed.
2/ Arrange the ‘cruising’ gear to have the BEST chainline. The sprocket that is 46mm out.
3/ Arrange the ‘climbing’ gears to be using the sprockets that are riveted together.
4/ Use a rear wheel that has a Steel freehub body.
5/ If the rings are more than 12 teeth different, fit a Dog Fang.
6/ Have the chain 1 full link shorter than the Shimano recommendation.
7/ Fitting a MTB triple chainset to a road frame requires a Bottom Bracket 8mm narrower than the Std BB.
8/ Fitting a MTB triple chainset to a road frame and disregarding the large ring, requires a BB 6mm narrower than the Std BB.

"Cruising gear", is the one where you are using 50% of your FTP and your most efficient cadence.
Last edited by Ayesha on 5 Jul 2013, 9:26am, edited 1 time in total.

reohn2
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Re: Compact double chainset with square taper and 46T chainr

Postby reohn2 » 5 Jul 2013, 9:26am

OnYourRight wrote:
reohn2 wrote:Stronglight Impact is 8sp compatible and is an excellent choice :)

It worries me slightly that the Stronglight website says the Impact is for 9/10-speed chains, here and here.
.


I'm currently running four S/light Impact chainsets,two on 9sp(one of which is on a tandemand the timing chain is 8sp)and two on 8sp one is running an 8sp chain and the outher a 9sp chain,I also run the two 8sp with 7sp cassettes and chains(which are 8sp compatible) and even run a 9sp chain on one of the 7sp set ups :)
All Shimano and all run perfectly :D
BTW all with Sram chains but I'm confident that Shimano/Wippermann/KMC or even Campag chains would run just as good :) .
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andrew_s
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Re: Compact double chainset with square taper and 46T chainr

Postby andrew_s » 5 Jul 2013, 9:51am

niggle wrote:If that is how you read it then they also officially support using the ST-2300 double STI with a triple chainset :? I think I have heard of problems reported with broken shifters, or at least indexing issues due to the trim clicks on a left hand triple STI when using it with a double chainset.

What causes problems is when you use inner and middle shifter positions for your 2 chainrings.
If using a triple shifter on a double chainset, you should use outermost clicks with the lower limit screw blocking off what would be the granny position.

OnYourRight
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Re: Compact double chainset with square taper and 46T chainr

Postby OnYourRight » 5 Jul 2013, 10:02am

It’s reassuring that so many of you experienced people think the Stronglight chainset would work well with an 8-speed chain and indexed shifting. I presume you also think that for the Stronglight Impact double, not just the triple.

niggle wrote:Maybe not going to the Alps this year.... but why limit yourself unnecessarily?

For the sake of simplicity while riding, ease of setup, lower Q-factor, clarity of purpose, and all the other reasons some people prefer doubles to triples, and others prefer a single chainring, and some even prefer a fixed-gear bicycle!

You can turn this into a whole philosophy, but I just feel the compact double strikes a good compromise between my desire for simplicity and my desire for optimum cadence. It helps that I go up hills faster than most (or did, when I last had a bicycle) and my top speed is relatively low, so my range of needed speeds is moderate.

Thanks for your advice, Ayesha. Tip 1: a 100+ inch gear will definitely feel laboured at my cruising speed! What’s “FTP”, though? Tip 2: this is my main consideration. Tip 6: any particular reason for that?

OnYourRight
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Re: Compact double chainset with square taper and 46T chainr

Postby OnYourRight » 5 Jul 2013, 12:27pm

Eventually found this note on the Stronglight website, which says that the chainsets labelled 9/10-speed are also compatible with 8-speed systems.

Not that I didn’t trust you lot! You’re clearly immensely knowledgeable about this stuff.