Are chainrings (5 bolt) universal

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Are chainrings (5 bolt) universal

Postby gururug » Sat Feb 17, 2007 11:51 pm

Hi all,

My Avanti Giro (XS) came with 170mm cranks. The rest of the running gear is the new 10speed 105 but the crankset is FSA gossamer. I am surprised that an XS sized bike is fitted with 170mm cranks but I am slowly learning that many cycling equipment manufacturers do not cater for small/tall riders very well !!!

Not keen on forking out 500$ for a whole set I have located some second hand Ultegra cranks (minus the chainrings).

What I want to know is;

a) will the chainrings off the gossamer crankset fit on the ultegra right crank.

b) is it/why is it mandatory to use an ultegra bottom bracket? or will the gossamer bottom bracket suffice. (from what I can see I should be able to just unscrew the five bolts, swap the chainrings and screw on the ultegra cranks).

Once again, thanks for all the help!

Oh yeah, if they won't fit, can anyone suggest a solid/cheap solution. i.e.

a) get 165mm gossamer compatible

b) order the 105 full crankset to bring up to speed with the rest of my running gear

c) bike shop/recycler in sydney that may have a few 165mm crankarms sitting around?
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by BNA » Sun Feb 18, 2007 8:53 am

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Postby europa » Sun Feb 18, 2007 8:53 am

Go ye to Sheldon Brown :D

Chainring Interchangeability

Basically, you may or may not be able to make the change but some simple measurements will tell the tale.

With the bottom bracket, the Ultegra cranks may not fit the Gossamer - again, there are various types and you'll have to have a look, though I reckon you'd be unlucky not to be able to bolt the cranks straight on.

Richard
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Postby heavymetal » Sun Feb 18, 2007 9:58 am

Some of the Shimano equipment has different sized fingers on the same cranks. It's mainly the triples that have this problem.

There is a measurement taken across the fingers, which measures the diameter of the bolt pattern.

I have found Shimano Australia have been very helpful when the LBS rings them regarding things like this. However regarding other things they say no when it does work.
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Postby mikesbytes » Sun Feb 18, 2007 10:19 am

The temology you are looking for is BCD, which stands for Bolt Centre Diameter. You probably have a BCD of 130mm and if so, you should be able to use your chain rings on another BCD 130mm crank.

If you are running 10 speed, then get one for 10 speed as the chain rings will be slightly closer together.

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Postby gururug » Sun Feb 18, 2007 10:46 am

There's writing on the outside of the large chainring that says;

BCD 110mm

So, I now have to find a manufacturer that makes;

-110mm-BCD
-165mm cranks/sets
-10speed compatible (thinner crank separation)

SO MUCH FOR STANDARDS! No wonder people recomment
purchasing a whole crankset. Well, if I can't easily source
some compatible arms, looks like i'm going to have to fork
out 400-500.

Thanks again dudes.
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Postby mikesbytes » Sun Feb 18, 2007 11:29 am

BCD 110mm is also known as a compact crank set

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Postby LuckyPierre » Sun Feb 18, 2007 11:41 am

It seems to me that you are up for both bottom bracket and crankset - mainly because most contemporary 10-speed cranks have an 'integrated bottom bracket'. The spindle is integrated with the chain ring spider and the 'bottom bracket' is really two external bearings.
Shimano cranks support a 130mm BCD (yours seems to be 110mm).
Haunt eBay for a while, they're sure to turn up!
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Postby LuckyPierre » Tue Feb 20, 2007 10:29 am

I've gone back over this thread and i think that there's a couple of things still to clarify.
Things that we know:
FSA Gossamer cranks
170mm
110 BCD
That suggests that is a compact crankset (as some-one, it was Mike, pointed out), but the clincher will be in the chain rings. Does it have 53 - 39 tooth rings or 50 - 36 or some other combination?
Something in the back of my head tells me that most crank length recommendations apply to normal (53 - 39 tooth) cranks, not compact ones. I'll do some searching and try to verify it, but has anyone got any ideas?
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Postby Mulger bill » Tue Feb 20, 2007 10:35 am

The FSA Gossamer runs an external BB, is there any compatibility with other makers?
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Postby mikesbytes » Tue Feb 20, 2007 10:53 am

As a rule of thumb, your crank lenght is 1/4 the length from the bottom bracket to the top of the seat, measured up the seat post.

This is a guideline, after that its personal preference.

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Postby gururug » Tue Feb 20, 2007 10:54 am

Website says its a 36-50T. MY crank to seat is 650mm so 1/4 this is 162.5, i think keeping the 170mm might do some damage in the long term.

This might help,

http://www.avantibikes.com/road-comp/giro.aspx?bid=7

Looks like shimano, truvativ, specia. TA all offer 165mm cranks.

http://www.specialites-ta.com/produits/ ... ls1_gb.htm
http://www.sram.com/_media/pdf/en/truva ... nksets.pdf

Although the specialities may offer even shorter than 165 I think these migh be difficult to source unless I order from o/seas or an LBS.


I assume a non-compact will fit in where my compact comes out?
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Re: Are chainrings (5 bolt) universal

Postby LuckyPierre » Tue Feb 20, 2007 11:34 am

gururug wrote: ... I have located some second hand Ultegra cranks (minus the chainrings) ...

If the Gossamer cranks are compact (which it seems like they are), then you won't be able to fit the Gossamer chainrings to an Ultegra crankset - the BCD's are different.
You could replace it with an Ultegra crank, but you would have to re-locate the front derailleur to accommodate the larger chain rings.
Shimano make a compact crank (FC R700) that come with 165 mm crank arms, but I haven't seen one in stock in any of the online shops I visited.
The Gossamer compact crank also comes with 165 mm arms, but the same availability applies.
The thought in the back of my head (about compact cranks and crank lengths) didn't rate a mention in any of the articles I looked at.
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