fskywalker

Hi folks, I like a lot the idea of owning a cassette with an upper number over 27 (for heavy climbing) and recently came across the 2009 Shimano DA unit in 11-29 configuration. My bike has Shimano 7800 DA components and wonder whether that cassette will work with the existing system or would I be force to replace anything?

Thanks,

Francisco

BikeWNC

It's an 11-28 cassette not 11-29. I've been using a SRAM 11-28 cassette on my 7800 group and it works fine so I expect the Shimano one would work also.

BobLoblaw

Some say a 27 is as big as you can go with a short-cage (i.e. racing) derailer. A medium or long cage would work for sure.

BL

fskywalker

You are right, I meant 11-28. Is someone using the one from Shimano? Just want to make sure before I buy it.

Regards,

fskywalker

I think that my rear derallieur is short cage, not long (will check). I never hear about medium cage, is that available on 7800 series Dura Ace?

2cyl

you must have seen the pbk offer for a 7900 cassette with free chain!

fskywalker

Hi BikeWNC, is your setup double or triple? (So, is your rear derallieur short or long cage?)

Booger

They took a page out of the Performance book. The cassette was < $200 last week, so discount might be a better word than free. Blows my mind that prices are still that high.

merlinextraligh

Shimano says the 11-28 won't work with 7800, which means they won't warrant that it will work to their standards.

In actual practice it will work fine. Make sure you have enough chain that it will fit in the big big combination.

And you'll likely want to stay out of the small small (the amount of chain wrap from a short cage derailleur is the reason Shimano doesn't reccommend it )

ericm979

[QUOTE=BobLoblaw;9029236]Some say a 27 is as big as you can go with a short-cage (i.e. racing) derailer.
[\QUOTE]

27t is the max cog size for short and long cage shimano derailleurs, according to shimano. But their spec is conservative. You can go to a 28t cog on the short cage and 30t on the long cage unless the frame has an unusually short derailleur hanger.

Chain wrap is another issue. With 50/34 chainrings and a 12-27 cassette the wrap is already over Shimano's spec of 29t. An 11-28 paired with 50/34 chainrings may require a long cage rear derailleur to take up the wrap.

PanicDog

I have a DA 7800 short cage rear derailleur and I use a SRAM 11-28 cassette with a FSA 50-34 crankset. The shifting is fine.

I can get into the 50-28 just fine. I can also get into the 34-11, but I notice a lot of noise when in that gear combination. I think it is from the slack in the chain.

Everyone always says avoid the 50-28 and 34-11. Why is that though? In the 34-11, is it just because the chain is in danger of falling off? What about the 50-28? As long as you have the right chain length, what is the problem with riding in that gear combination?

AEO

you have it backwards, avoid large ring, large cog and small ring small cog.

if your derailer is road short, it only has about 30T of chainwrap capacity, with a 34/50 and 11-28 the total teeth difference becomes (50 - 34) + (28 - 11) = 33 and your chain will droop in the small-small combo. if you have a road medium cage it has a 37T chainwrap capacity so it's not a big problem.

in the big-big combo, the chain attains a very bad angle, especially with short chainstays. This is both noisy and inefficient if you made your chain the shortest possible length with the gearing you have.


it's not that bad to cross chain in big-big or small-small if:
your derailer has the chain wrap capacity, like a MTB long cage with 45T capacity
you have really long chainstays, single 114link chain is not enough to cover the length + teeth difference
you made your chain a bit longer than the shortest possible by doing big-big + 2~3 links instead of just 1.

PanicDog

Sorry, I meant 50-28 and 34-11.

So avoid the 50-28 because it is noisy and inefficient?

Avoid 34-11 because the chain droops. Who cares if the chain droops?

I can live with replacing my chain more often if it means I don't have to worry about not using some of my gear combinations.

As long as I keep everything clean and shifting smoothly, is there any reason other than premature wear not to use those gear combinations?

BikeWNC

AFAIK, it's a standard short cage rear 7800 der. on compact double 50/34 setup. Works just fine. I have two bikes with that gearing. My 7970 setup has the same gearing with the 11-28 Shimano cassette.

AEO

chain droop = dropped chain, chain suck and chain slap.

dropped chain, you can fall off your bike if you don't expect it.
chainsuck can destroy your chainstay and chainrings.

well, I don't care about you, since it's you and your bike.
but on my bikes, I like to avoid those problems.

uspspro

Uhh, because it will be banging on your chain stay with every little bump.

PanicDog

Hmmm, I'm not sure if my chain will hit my chainstays in the 34-11. I've never heard or felt it. I will test it out.

I don't see how a drooping chain would be any more likely to cause chain suck.

Can any damage be done in 50-28?

AEO

only if the chain is too short.
then you can destroy your RD and RD hanger.

you probably have a medium cage if there's no chain droop in small-small.

ericm979

That's because your short cage derailleur can't take that much slack. A slack chain is bad for all the reasons that the other posters have explained. Chain suck is not a good thing, it can destroy your frame.

On many 50/34 cranksets the chain will rub on the 50t ring when on the 34t ring and the smallest cog or two cogs. Shorter chainstays on the frame make this worse. There is nothing you can do about it. Don't use that combination.

If your chain is not slack in the 34x12, then you are ok. If it is, you need a long cage derailleur. I am assuming that your shop set up your chain length so it just makes it over the 50x28, which is correct. Even though you should not use that gear combo either, the chain should be long enough to handle it in case you shift into it by mistake. If it is not and you shift into the large ring/large cog then you'll destroy the derailleur, hanger or frame.