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Please Help: Changing from compact 50/34 (12-25 cassette) to 53/39 and ???

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Please Help: Changing from compact 50/34 (12-25 cassette) to 53/39 and ???

Old 04-27-13, 09:52 AM
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Please Help: Changing from compact 50/34 (12-25 cassette) to 53/39 and ???

Hi Bike Experts-

I inadvertently bought a 53/39 crankset to replace my current rings/cranks which happen to be compact 50/34(old FSA junk to new Carbon Centaur), and currently have a 10-speed 12-25 cassette which also needs replacing.

I live in a relatively flat city (London, England), and use this bike as a commuter. I tend to ride in the big ring 90% of the time on my current set up. I'm not sure if I've ever had to go to the lowest (i.e., easiest) on the small ring. Sorry, my bike knowledge is limited to riding and changing tubes.

What cassette should I buy? I don't want to have to buy new derailleurs if possible, though they may need replacing soonish so that isn't an impossibility if necessary (I do realize I'll need a new chain; does which cassette/crankset dictate what length I need)?

Thanks so much in advance.
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Old 04-27-13, 10:17 AM
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You could stick with your current 12x25 gearing and the new crank will just increase both your highest and lowest gears. If you do have hills and sometimes use your lower gears, a 12x27 will give a bit lower low gear.

Chains typically come too long for most gear trains and have to be shortened a few links no matter what gearing you use. Get a new chain with the new cassette and crank and size it to fit. Sheldon Brown's web site gives a very good method for sixing chain length by wrapping the chain around the biggest chainring and biggest cog (bypassing the rear derailleur) and adding 1" (two links). That length guarantees you can shift into big-big without causing damage.
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Old 04-27-13, 10:39 AM
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I'd try the existing cassette and see if your lowest gear is low enough.
Your 9th gear would be very close to your existing 10th gear.
IF NOT low enough, consider a 12-27/28. Your lowest gear would be quite close to your current lowest gear. (just a bit higher)
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Old 04-27-13, 10:47 AM
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Originally Posted by HillRider
You could stick with your current 12x25 gearing and the new crank will just increase both your highest and lowest gears. If you do have hills and sometimes use your lower gears, a 12x27 will give a bit lower low gear.

Chains typically come too long for most gear trains and have to be shortened a few links no matter what gearing you use. Get a new chain with the new cassette and crank and size it to fit. Sheldon Brown's web site gives a very good method for sixing chain length by wrapping the chain around the biggest chainring and biggest cog (bypassing the rear derailleur) and adding 1" (two links). That length guarantees you can shift into big-big without causing damage.
Thanks for the reply.

Is keeping 12x25 ideal then? I'm really not fussed at all.
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Old 04-27-13, 10:48 AM
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Originally Posted by Bill Kapaun
I'd try the existing cassette and see if your lowest gear is low enough.
Your 9th gear would be very close to your existing 10th gear.
IF NOT low enough, consider a 12-27/28. Your lowest gear would be quite close to your current lowest gear. (just a bit higher)
Lowest meaning the biggest ring, right?

By moving up to a 27/28 it means it would be easier to peddle? Thanks.
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Old 04-27-13, 10:50 AM
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Originally Posted by brokentelephone
Lowest meaning the biggest ring, right?........
No
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Old 04-27-13, 12:47 PM
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You're asking a question that only you can answer.

None of us has to ride your bike through your neighborhood using your body so there's no way for us to know what gears you should have.
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Old 04-27-13, 01:19 PM
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Originally Posted by brokentelephone
I'm not sure if I've ever had to go to the lowest (i.e., easiest) on the small ring.
Hi,

Your big chainwheel has gone up about half a gear (6%) and the small chainwheel about a
gear (15%). Doesn't sound like that would be problem with your current rear gear cluster.

rgds, sreten.

Last edited by sreten; 04-27-13 at 01:23 PM.
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Old 04-27-13, 02:03 PM
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i agree. you could stay with a 12-25. if you have been riding mostly in the big ring, and you are staying mostly on flats, you probably don't need to get any bigger cogs on the back (for climbing).

for the chain, do you need a new one just to increase the length for the new chain rings? i'm not 100% sure that you need that, or is it b/c the chain is getting stretched and needs to be replaced?

normally, it is recommended that you change the cassette and chain together, but that is due to wear. if you are only thinking you need a new chain for added length, you MIGHT only need to add a few links. (other people may want to weigh on on this).

From what i can tell about chain length, it's mostly eye-balling the length once you get your chainrings and cassette settled. there are various videos on youtube that illustrate this.
if i'm only changing them out due to wear, i usually just count the number of links on my old chain and use that for my new chain. (if i'm not changing the number of teeth on my cogs).
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Old 04-27-13, 02:40 PM
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34:25 is like a 39:28.6 ... 1.36:1 about..

neither easier to pedal or harder , just about the same..
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Old 04-27-13, 02:47 PM
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You could try a 12/13-30T cassette - a 30t rear cassette should work w/ a road derailler.

The specs on your crank show the 5-Bolt Chainring's BCD is 110mm; so any compact rings should fit (and be the same as a cassette). If your crank is new, you could easily sell or trade your 53/39 rings to a racer.

I can't see why you would need a 53 ring, even with 12T rear cog (let alone 11), it is hard to keep up cadence with a 53 up front.

I run 48/38 up front with an 11t smallest in rear (but I have 130 bcd cranks and 38t is the smallest). My gravel/ cross/ MTB (Lemong Poprad) runs an 11-34t cassette w/ a MTB rear derailleur.


Originally Posted by sreten
Hi,

Your big chainwheel has gone up about half a gear (6%) and the small chainwheel about a
gear (15%). Doesn't sound like that would be problem with your current rear gear cluster.

rgds, sreten.

Last edited by Erik_A; 04-27-13 at 03:00 PM.
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Old 04-27-13, 03:09 PM
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Originally Posted by Erik_A
.......I can't see why you would need a 53 ring, even with 12T rear cog (let alone 11), it is hard to keep up cadence with a 53 up front........
If you read his post....
"I inadvertently bought a 53/39 crankset to replace my current rings/cranks which happen to be compact 50/34......."
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Old 04-27-13, 03:17 PM
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I know, I was speaking generally - there is no need for a 53 big ring at all in a standard crank now that 11T cassettes are the norm. You can always special order one if your legs are like tree trunks!

Originally Posted by Bill Kapaun
If you read his post....
"I inadvertently bought a 53/39 crankset to replace my current rings/cranks which happen to be compact 50/34......."
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Old 04-27-13, 04:26 PM
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You'd get pretty close to the old gearing with a 13-29T cassette. (Campy, right?)
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