Changing chain rings

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Changing chain rings

Postby Cicada » Tue Feb 19, 2013 2:13 pm

Hi all,

Firstly apologies if this is in the wrong section, mods please feel free to move it.

Secondly, I am pretty new to this, been commuting for about 18 months after having not ridden since I was a kid, so if what I am proposing is ridiculous or any info I have given seems incorrect, please feel free to suggest something else.

OK, so I have an old Giant road bike currently used as a commuter that I am about to upgrade. It is old and very ordinary, but I would still like to use this bike as a back-up, however my issue is the chain rings. I recently moved to a very hilly area in the Dandenongs, as such my commute now finishes with about 3km of fairly taxing (for me anyway) uphill climb.

The Giant has a 52/42T double, which from what I have been able to gather, is larger than what would be considered standard.(?)
What I am wondering is if I would be able to swap this out for say, a 50/34T or something similar with a view to getting up the hills easier? I would be happy to replace the whole crank set at at the same time as the existing one appears to be damaged and is sliping out of the bracket.

I don't really know what is involved, so I guess that is what I'm here for. Can I do this without changing the front derallieur? What components would I need to replace? Is it a relatively easy job or not so much? What indicators do I need to look for to know what parts will be compatible when looking to buy?

here are some photos for info...




I pass it over to the brains trust! Any info would be much appreciated, thanks guys!!
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by BNA » Tue Feb 19, 2013 2:25 pm


Re: Changing chain rings

Postby simonn » Tue Feb 19, 2013 2:25 pm

Yes. You can. You would need a new crankset, because the BCD (Bolt Circle Diameter) for a compact is 110 rather than 130 like you have. The smallest chainring you can get for a 130 is 38. However, a 38 might be small enough for you? Would almost definitely be cheaper - ... trochri300 . Probably would not shift as well...? Might be worth considering going 48/38 because the derailleur might be designed for a 10t difference.

If you do get a new crankset, you would probably need a new bottom bracket as well. If you also get an external bearing BB (all modern cranksets really, except OTTMH stronglight impact and FSA vero - check chain reaction cycles), you would probably need to get the BB shell faced and chased as well - visit to bike shop $20-30 or so.
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Re: Changing chain rings

Postby Graeme H » Thu Feb 21, 2013 2:54 am

Hi Cicada,

If you want to stick with older style parts to match your bike, you can still buy new compact cranksets for square taper bottom brackets like yours, eg ebay item 120984596818.
You might also be able to find something second hand.

The reasons you might need a new bottom bracket are:
(1) the alignment of chain rings might need a different length bottom bracket axle (the one mentioned above fits best with a 110mm axle), or
(2) if you get crank arms with a different type of mounting that's not compatible with your existing square taper bottom bracket axle, like simonn described.

You could buy just the axle in the length that you need (eg ebay 320947790705) or a complete bottom bracket with newer type bearings (eg ebay 150928140799).

If you significantly reduce the size of your chainwheel, then you might need to shorten your chain to match.
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Re: Changing chain rings

Postby Dan » Thu Feb 21, 2013 8:00 am

Cicada, I think I have a spare 38 or 39 inner ring if you're after a cheap tester. 52/39 is a good front range, you can work with cassette variation from there. PM me if you want.

EDIT: corrected user name, like how embarrassment.
Last edited by Dan on Thu Feb 21, 2013 8:19 am, edited 1 time in total.
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Re: Changing chain rings

Postby silentbutdeadly » Thu Feb 21, 2013 8:11 am

Cicada..if you can't source chain rings then I'd suggest something like this for you ... /??pr=1163 a cyclocross chainset in 46-38. The similar Shimano CX-50 chainset should be a bit cheaper...

Otherwise I'd go with the 48-38 chainrings but even a basic pair of FSA Pro Roads in 130 BCD will set you back the best part of $100
Ours is not to reason why...merely to point and giggle
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Re: Changing chain rings

Postby Cicada » Fri Mar 08, 2013 12:32 pm

Thanks for the info everyone, will have a think about what to do. Don't want to spend much on it, as it's not really worth much.
I am leaning towards GraemeH's suggestion of new BB or new axle.

I'll check back in when I decide what to do and no doubt need more advice.

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