tj90

I currently running 39-26 combo for climbing >10% grades during double centuries. Its killing me. I want to get a bigger cassette to fit my 9 speed campagnolo system. What is the max teeth I can get away with without having to buy a new derailleur or compact cranks? I think I remember seeing veloce 28 teeth cassettes. Miche has a 28 tooth cassette too. Wonder if a 29 tooth exists. Any option has to work with short cage derailleur?

DaveSSS 

A Campy 13-28 may work, but it depends on the RD hanger length and the chainstay length. Chainstays that are the perfect length can gain up to 3T of wrap compared to the worst case.

Use the "rigorous" formula for chain length at the Park website. If your chainstay length suggest a length that is close to a whole number, (52,53,54) then you have the best case.

HillRider

Neglecting wrap capacity for the moment, will the jockey pulley clear a 29T cog? If so, then all you will sacrifice is a couple of the small-small gear combination if you exceed the wrap capacity.

tj90

Dave - I appreciate the response. I used the chain calculator and found that with a 41cm stay, 53/28 combo, I need 53.77in of chain or 54in. Im currently running 53in with my 26 tooth (probably too long so chain length shouldnt be a problem. My concern is the top pulley bottoming out on the cassette.

fietsbob

Look into a compact crank then the front can be a 34t, 50x12 should be high enough for mortals.

think 29 in the 10 speed cassette may work .. need mind the chain length
IRD campy compatible cassettes go larger , though would compel long cage ..

tj90

Definitely looks like compact is a sure bet. However I did find this info from Branford below. If I was to run a 53/39 and 13/28 miche I would have a CW of 29. Just 2 points higher than campy recommended 27 on a short cage. Branford confirms that campy short cage will shift into a 29 just performance may not be optimum.... Only $41 for the miche may be worth it for science sake.
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Chain Capacity and Cage Length
Campagnolo officially recommends various rear derailleur cage lengths for use with specific cassette and double or triple chain ring combinations. However, it is important to understand that any 1999 to current, Campagnolo 10 speed rear derailleur, will shift up to a 29 tooth cog and down to an 11 tooth cog. The problem you will run into is that the derailleur cage may not be long enough to take up all the slack in the chain for a wide range. Thus Campagnolo recommends using a short cage derailleur with a maximum cassette cog size of 26 teeth even though it will shift to a 29 tooth cog. Chain wrap or CW is a helpful concept to understand when you need to determine proper derailleur cage length.

Current Record, Chorus, Centaur and Veloce 9 and 10 speed rear derailleurs use the same three cage lengths; 55, 72.5 and 89 mm measured from the center of the upper jockey wheel to the center of the lower jockey wheel. 55 mm cages have a chain wrap value of 27; 72.5 cages have a CW of 36 while 89mm long cages have a chain wrap value of 39.

Chain Wrap is a simple calculation that will help you determine whether the rear derailleur you choose has a long enough cage to take up the chain slack in your drive train. The shorter the cage, the lighter and stiffer the derailleur and the quicker it will shift. Calculate Chain Wrap to get the greatest shifting performance.
To calculate Chain Wrap Capacity determine the difference between your largest and smallest chain ring. Then determine the difference between your largest and smallest cog. Add the differences and you have Chain Wrap Capacity.

Example: 42/52 chain rings and a 12/21 cassette yields a CW of 19. 52 - 42 = 10. 21 - 12 = 9. 10 + 9 = 19. So, with a 42/52 chain ring and a 12-21 cassette you would need a rear derailleur that has a Chain Wrap Capacity of at least 19.
For a 39/53 and a 13/26 combo you will need a minimum CW of 27. 53-39 = 14. 26 - 13 = 13. 14 + 13 = 27. In practice the CW numbers are flexible by one or two points. You could use a 39/53 with a 12-26 cassette with a CW of 27 even though the calculation calls for 28.

tj90

Well I ordered the miche 13-28 cassette and it works perfectly. The short cage works no problem. The 28 tooth gets me close to compact crank with my old 26 tooth cassette without readjusting FD and or crankset swaps.... Cant wait to hit the sierras!

FBinNY 

yes the jockey wheel height on short and medium cage Campy RDs is the same, so clearing a 28t isn't the issue in any way.

The real issue is chain wrap capacity which is 27t on a short cage RD. With very careful chain measurement it might be stretched a bit to 28 or 29t but that's a matter of luck.

The OP can reduce his chainring differential by a few teeth, or live with inadequate chain take up for the small ring and smaller cassette sprocket combinations. If he goes that route he shouldn't try to fudge shorter than enough for the big/biggest combination because the consequences of accidentally shifting to are too severe.

rm -rf

A Campagnolo 13-29 on a 10 speed short cage with my 50-34 chainrings is fine on my bike. The small-small combination is pretty close to the limit, though. The big-big combination is fine, it isn't near being stretched out. It probably does depend on the exact bike chainstay lengths, etc.

The 34-29 low gear is really nice on long 7% or higher grades. To recover, I can slow down, with a low cadence, and not have to push really hard on the pedals. I'd be standing up on a 34-25 at those low speeds.

Thanks, tj90, for the clear explanation of chain wrap. I have the 55mm short cage, and am able to do a chain wrap of 32, where the "official" limit is 27.

Woj75

Hello,
I am building a 9 speed Record setup and saw that you were running that on your bike at the time of the post. Are you still running that setup and do you have any advice for me in regards to that configuration?
Thanks,
Woj75

cplager

Another option (that will likely require a new rear derailleur) is going for a triple. 39 -> 30 is a 30% drop in gear inches and definitely noticeable.