# switch out 53/39 for compact crank?



## z3phrn (Mar 19, 2011)

I've got an FSA Gossamer bb30 crankset with 53/39 teeth, and was thinking of trying out a 50/34 setup to see the difference.

Is any crankset that uses bb30 going to work (SRAM Force, FSA Gossamer)? The rest of the bike is shimano 105. I'm not sure if I'm overlooking some sort of compatibility issues with the front derailleur.

If it does work, what are some good recommendations for solid bb30 34/50 compact cranks? The only two I've looked at are the SRAM Force and the FSA Gossamer. Thank you!


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## bigbill (Feb 15, 2005)

Do you need the lower bottom end (34)? If you don't and you're only interested in a smaller big ring, you can get a 50 for your current crankset. The thing to consider when swapping to a compact from a standard, 50/34 is a 16 tooth jump versus 14 for a standard. Unless you need the 34 for a bailout gear, switching between the big and small ring on the front will involve more shifting in the back. 38T is as small as it gets for a stardard 130 crankset. I remember a 37 years ago but you had to file the spider to make it work. 

BTW, you can get a Stronglight Zircal 50T chainring from Ribble for $34. I have them on my commuter and they're very durable and shift well.


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## durielk (Jan 8, 2011)

You got hills.... go for it. You want speed too, upgrade to an 11 on the rear and you'll have about every move covered. If your in a not so hilly area, it will mean less shifting in the front for you. You'll ride everywhere in the big ring, if you see a hill over 6%, one shift and your done.


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## rx-79g (Sep 14, 2010)

Compacts just change you gearing - nothing else. Cassettes are cheaper than cranks, so you usually only go to a compact when you are already using the largest spread your derailleur can handle (like a 12-28).

Cranks are pretty expensive ways of adjusting gear ratios.


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## Ventruck (Mar 9, 2009)

rx-79g said:


> Compacts just change you gearing - nothing else. Cassettes are cheaper than cranks, so you usually only go to a compact when you are already using the largest spread your derailleur can handle (like a 12-28).
> 
> Cranks are pretty expensive ways of adjusting gear ratios.


I would go by this. OP, sounds like you've got a case with getting the torque at the moment. Finding a lower gear is less effective (cost effective at that) via chainrings. Matching up to your old ratios on the cassette will mean you slide about 2 cogs over, but even then you're pushing a heavier gear which is the wrong direction. At some point when you develop, you might be cross chaining.

Finding the1st-3rd gears easier on the cassette is what you're hunting for at the moment and in "bailout" situations. No need to compromise the rest of the cassette's overall range.


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## z3phrn (Mar 19, 2011)

Oh, sorry for not providing more details. I want to switch to a 50/34 so I can more confidently hit the hills. I figured that I would need a whole new crank for that. I was just concerned with compatibility issues with the shifters, if there were any.



Edit: I did not realize the chainring comes off the crankset. So I should just go buy a 50 and a 34 chainring! One more question: do I have to buy a 50/34 chainring as a set, or can I buy each piece and screw them together? I'm not sure if they come welded together or if they come one by one.


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## AvantDale (Dec 26, 2008)

If your riding a 53x39, your BCD is probably 130mm. You will not be able to fit compact rings on there. You'll need a 110mm crank.


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## z3phrn (Mar 19, 2011)

AvantDale said:


> If your riding a 53x39, your BCD is probably 130mm. You will not be able to fit compact rings on there. You'll need a 110mm crank.


Blah, you're right! Guess I'll have to get a new crankset. I did notice that the front derailler can move along the piece that is screwed into the bike, so I there there should be no compatibility issues with the smaller compact crankset. Does anyone know of any compact cranks that use bb30 (besides sram force and the fsa ones)?


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## SystemShock (Jun 14, 2008)

For BB30, I think it's mostly SRAM, FSA, and Truvativ right now. There is (was?) also a Cannondale crank that you could hunt down on eBay pretty easily (if they're not still being sold new), and there's a few small boutique brands making 'em too.

There was an interesting (if somewhat old) thread about the subject over at Weight Weenies... six pages of silliness with some occasional good nuggets of info:

http://weightweenies.starbike.com/forum/viewtopic.php?f=3&t=61116


/ Btw, what cassette are you currently running, Z3? A switch to 12-27 wouldn't cut it against those South Bay hills, eh? 
Some of 'em are pretty steep. 
.


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## durielk (Jan 8, 2011)

You will need to adjust your chain lenght. Everything else should work. You will need to adj you FD down.


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## z3phrn (Mar 19, 2011)

SystemShock said:


> For BB30, I think it's mostly SRAM, FSA, and Truvativ right now. There is (was?) also a Cannondale crank that you could hunt down on eBay pretty easily (if they're not still being sold new), and there's a few small boutique brands making 'em too.
> 
> There was an interesting (if somewhat old) thread about the subject over at Weight Weenies... six pages of silliness with some occasional good nuggets of info:
> 
> ...


Thanks for the info, I've learned a ton! I've got a 11-25 cassette right now. Switching to 12-27 or 11-28 would be a interesting switch to try as well. To be totally honest, I'm not too worried about climbs; I'm just a bike parts noobie who wants to get an overall feel for different gearing combos. 

I guess that leads to a further question... would I just be able to change out the last ~2 (or however many so shifting doesn't become weird) cassette sprockets to a higher teeth count and call it a day ?


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## SystemShock (Jun 14, 2008)

z3phrn said:


> Thanks for the info, I've learned a ton! I've got a 11-25 cassette right now. Switching to 12-27 or 11-28 would be a interesting switch to try as well. To be totally honest, I'm not too worried about climbs; I'm just a bike parts noobie who wants to get an overall feel for different gearing combos.
> 
> I guess that leads to a further question... would I just be able to change out the last ~2 (or however many so shifting doesn't become weird) cassette sprockets to a higher teeth count and call it a day ?


IIRC, the last 3 sprockets on most cassettes (well Shimano anyway) are on the same spider/carrier/whatever... someone correct me if I'm off. So yeah, you likely could swap out the 21-23-25 you have now for the 21-24-28 on the tail end of an 11-28 cassette, giving you... the exact same cassette if you'd just bought an 11-28. 

Not sure if you can just buy that 3-sprocket assembly as a stand-alone... or if you can, if to do so is all that much cheaper than just buying a new cassette. 

Personally I don't even like 11-28 cassettes because of the big jumps in them, like from the 15 to the 17. 
I think 12-27 is a better cassette (if you hardly ever use the 11), but that's me.
.


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## durielk (Jan 8, 2011)

If you use the 53/39 & 11/28 cassette, your pushing the capacity of the RD, on a typical road bike. Or use a 12/28 and be on the borderline. Usually people change their bike for a reason, not just to see what it would be like. It only changes the top end or bottom end of the speed window, one usually selects the gears dependant on the ride topology. This post is making less & less sense.


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## SystemShock (Jun 14, 2008)

Btw, I'm assuming Z3 has a 10-spd cassette currently?
.


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## Len J (Jan 28, 2004)

Before you change.......run a gear chart at your normal cadence and speed and make sure your most used gearing doesn't have you either cross-chained or continually shifting back and forth be teen the rings.....it can be a PITA.

Len


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## z3phrn (Mar 19, 2011)

I changed to a 50/34 and it seems like I need to do the following (but I'm not totally sure):

-Lower the front derailleur a little bit. I think I will also need to add more tension to the derailleur cable, since its physically closer. 

-Remove chain links: going form a 53/39 to a 50/34 means that I should remove 53 - 50 = 3 chain links?

-Do I need to do anything with the rear derailleur?


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## rx-79g (Sep 14, 2010)

z3phrn said:


> I changed to a 50/34 and it seems like I need to do the following (but I'm not totally sure):
> 
> -Lower the front derailleur a little bit. I think I will also need to add more tension to the derailleur cable, since its physically closer.
> 
> ...


You'll need to lower and reset the front derailleur. Assume you are starting from scratch.

3 teeth is 3 half links, or 1.5 inches of chain. So remove 1 link pair (1 inch), if you want to make a change.

The rear derailleur is what ultimately determines chain length, and that length is all the adjustment needed. None of the other derailleur adjustments are affected by the crank or chain.


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## durielk (Jan 8, 2011)

rx-79g said:


> 3 teeth is 3 half links, or 1.5 inches of chain. So remove 1 link pair (1 inch), if you want to make a change.


The chain only sits on 1/2 the sprockets, so (53-50)/2 would be 1.5 teeth. I would guess you could get by removing 1 link pair, or maybe none at all.


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## z3phrn (Mar 19, 2011)

Thanks for the advice. What would happen if I didn't remove any links?


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## wim (Feb 28, 2005)

z3phrn said:


> Thanks for the advice. What would happen if I didn't remove any links?


Depends on how the chain was cut originally (shortest possible, longest possible or in-between). Shift into the small front-small rear combo (34 x 11) and see if there's still a bit of tension on the rear derailleur cage. If there is and the chain isn't rubbing on any part of the derailleur cage, no need to remove any links.


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