Chainset configuration

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cavasta
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Chainset configuration

Postby cavasta » 29 Jun 2014, 9:09pm

I'm currently running a 10 speed Shimano 105 compact chainset (50/34) on my road bike with an 11-28 cassette and am thinking about changing the inner ring from a 34t to 36t. I've never quite got on with the 16t difference on the compact between 50t and 34t. I've tried a 52/39 chainset but that was a step up too far (though the 13t difference between 52t and 39t felt spot on). I've also tried an 11-26 cassette with the 50/34 chainset but didn't quite get on with that set-up either.

The 50/34 compact is an FC-5600 with 110 bcd/65mm centre to centre (5 bolts). Will there be any likely issues fitting a compatible 36t inner ring to the 50t outer? This will produce a slightly unconventional 50/36 chainset. It's been suggested that this inner will do the job:

http://www.sjscycles.co.uk/middleburn-1 ... prod31528/

All thoughts and advice most welcome.

Brucey
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Re: Chainset configuration

Postby Brucey » 29 Jun 2014, 9:44pm

I don't know if your specific setup will work perfectly but one thing to look out for is the minimum tooth difference that the front mech is designed for. The inner cage plate on compact double front mechs is very low and may very simply hit a larger inside chainring.

2T is unlikely to be show-stopper though; at worst it should be a case of raising the front mech a few mm. Is there likely to be a problem with this? No not really, although there may be an increased risk of unshipping the chain outwards off the big ring.

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Valbrona
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Re: Chainset configuration

Postby Valbrona » 30 Jun 2014, 1:36am

Can't see why a 36 inner won't work and can't see any 'unconventional' in this.

I don't speak Shimano but some cranksets need chainrings of a unique pattern, like with Dura-Ace. However, your 105 crankset looks to be to an orthodox design and will probably take regular 110BCD chainrings.
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cavasta
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Re: Chainset configuration

Postby cavasta » 30 Jun 2014, 1:30pm

Thanks for the replies. According to the technical document, the front mech will handle a chainset tooth difference of "15 teeth or less". It handles my compact chainset, with a tooth difference of 16, without problem and it did the same with the 13 tooth difference on the 52/39. So unless I'm missing something I'm assuming that it should work fine with the 14 tooth difference on my proposed 50/36 set-up.

I only referred to it as unconventional because 50/36 doesn't appear to be available as an option when buying off-the-peg cranksets. I can't for the life in me understand why as it makes perfect sense to me.

OnYourRight
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Re: Chainset configuration

Postby OnYourRight » 30 Jun 2014, 3:38pm

Another way to reduce the difference between the two chainrings is to make the large chainring smaller. That makes more sense to me. For example, my bike has a 46T/34T chainset.

robc02
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Re: Chainset configuration

Postby robc02 » 30 Jun 2014, 5:04pm

When "compact! chainsets were first marketed, 50/36 and 48/34 were standard offerings as I recall. %0/34 came a little later - at least with some brands.

I have a 50/36 on one bike and it works perfectly, although with a Campag front mech.

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[XAP]Bob
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Re: Chainset configuration

Postby [XAP]Bob » 30 Jun 2014, 7:59pm

Tech Doc wrote:"15 teeth or less"


Grr, 15 teeth or FEWER, not less.

Except in some very esoteric circumstances you can't get partial teeth.

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Brian73
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Re: Chainset configuration

Postby Brian73 » 30 Jun 2014, 8:30pm

I'm running a 36/50 Truvative Touro chainset using 9 speed Tiagra 4500 mechs and shifters. It was stock spec for the Halfords Carrera that it came off, works great

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CyberKnight
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Re: Chainset configuration

Postby CyberKnight » 30 Jun 2014, 9:42pm

I am considering the exact same change to my compacts as i just dont use the inner ring as the jump is so big i end up spinning away till my speed reduces enough to a usable gear so i normally end up just staying in the big ring and grinding up in 50x 19 or 50x21 .The 36 would make the jump a lot more usable and i believe you can get semi compacts that have 52/36 although as im not in training for races or fit enough anyway 50x12 does not get seen unless im going down hill !
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Valbrona
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Re: Chainset configuration

Postby Valbrona » 30 Jun 2014, 10:58pm

In terms of cadence, 34 can be a bit too small, but 36 can hit that cadence sweet spot for a lot of riders ... at the expense of losing ratios at the low end of your gearing. Give me a 36 inner or middle ring in preference to a 34 any day.
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cavasta
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Re: Chainset configuration

Postby cavasta » 1 Jul 2014, 10:19am

Thanks again for all the replies. 50/36 it is then :D

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hondated
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Re: Chainset configuration

Postby hondated » 1 Jul 2014, 10:30am

Thanks that's made me feel like a real wimp as I prefer a 30 to a 34 any day when it comes to climbing hills.

Ayesha
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Re: Chainset configuration

Postby Ayesha » 1 Jul 2014, 10:31am

A ‘Compact’ set is a touring set that is made to look like a road set so the casual onlooker thinks it’s a road set at first glance.

Ayesha
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Re: Chainset configuration

Postby Ayesha » 1 Jul 2014, 10:37am

I run a 22/44 double with a ‘dog fang’.
This gives me a 22” – 100” range over 15 unique ratios with a nine cassette.

Incidentally, if the number of teeth on the sprocket is the same as the wheel diameter in inches, the gear inches is the same number as the teeth on the chainring.

So I have a 27T sprocket and a 27” wheel. With the 22 chainring, that’s a 22” gear.

OnYourRight
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Re: Chainset configuration

Postby OnYourRight » 1 Jul 2014, 10:54am

CyberKnight wrote:I am considering the exact same change to my compacts as i just dont use the inner ring as the jump is so big i end up spinning away till my speed reduces enough to a usable gear so i normally end up just staying in the big ring and grinding up in 50x 19 or 50x21 .The 36 would make the jump a lot more usable and i believe you can get semi compacts that have 52/36 although as im not in training for races or fit enough anyway 50x12 does not get seen unless im going down hill !

If you don’t use 50T × 12T except downhill (where aerodynamics ensure you get very little return for your pedalling effort) then there isn’t much point keeping it around. That’s what motivated me to reduce the size of the big chainring to 46T.

This seems to me a good way to reduce the jump between the two chainrings while optimising the rest of the gear choices. For me, anything over 100 gear inches is pretty pointless to cart around. Better to optimise the large chainring for cruising.

Ideally my inner chainring would be smaller than 34T, but then I’d need an expensive touring chainset or a bodged triple of some sort.

Ayesha wrote:A ‘Compact’ set is a touring set that is made to look like a road set so the casual onlooker thinks it’s a road set at first glance.

I think my 46T big ring gives the game away!

Ayesha wrote:I run a 22/44 double with a ‘dog fang’.
This gives me a 22” – 100” range over 15 unique ratios with a nine cassette.

The 44T ring sounds lovely but the jump between chainrings must be enormous. I don’t mind a bit of a jump – I just shift at the back when I shift at the front – but a doubling of ratios seems excessive. Do you shift across most of the cassette each time you change the front?