50/34 + 11-28 + short cage

[PaMtbRider]

The thread on chain length got me wondering if anybody has tried the new shimano 11-28 cassette with 50/34 chain rings and a shimano short cage derrailleur. I am currently using a 12-27 50/34 combo which exceeds the wrap capacity of a short cage derrailleur, but works fine. Am I asking for trouble by pushing it to an 11-28 cassette and further exceeding suggested capacity?

[Tobias]

That combination would exceed the capacity of the older rear derailleurs, but the newer derailleurs in DA and Ultegra are rated for exactly that. I'll look it up again to double check but I'm pretty sure it's 33T for the short cage.

[Dave]

All you can do is try it. You should never use the 34/11. If the chain has some tension in the 34/12 now, it still will. An accidental shift to the 34/11 won't hurt anything.

One tooth is only 1/4 inch of chain. If you're not overextending in the big/big now, another tooth is not likely to break anything. Shift to that combo and see if there's some slack left in the chain. There's probably not much, but you don't need much. You shouldn't be using the big/big combo either.

The other issue is if the upper RD pulley will clear the the largest cog. Some folks have installed a longer B screw to fix that problem.

Remember the part of the discussion about all frames not being equal when it comes to chain wrap? Some can have up to 2T more than others. The wrap specs are always worst case.

[NRRider]

DA 7800 RD with SRAM 11-28. Just make sure your chain is long enough to handle the 28T. Otherwise works fine.

[dave thompson]

The thread on chain length got me wondering if anybody has tried the new shimano 11-28 cassette with 50/34 chain rings and a shimano short cage derrailleur. I am currently using a 12-27 50/34 combo which exceeds the wrap capacity of a short cage derrailleur, but works fine. Am I asking for trouble by pushing it to an 11-28 cassette and further exceeding suggested capacity?
The answer is: it depends. Depends on chainstay length. derailleur hanger position and careful attention to chain length. I've run an 11-28 and an 11-30 cassette using a short cage derailleur, both with no issues. With the 11-30 I had to screw the B-screw in quite a bit.

Most likely you won't have a problem with the 11-28 but with the 11-30 you won't know until you try it.

[Waldo]

I've run 50x34 and 11x28 on SRAM derailleurs with a Shimano chain. Complicating matters further, I use Rotor chainrings. Works perfectly... on my bike.

[PaMtbRider]

Thanks for all the feedback. The der. is a 7800 and I will be replacing the chain with the cassette. Since I am not an engineer, never worked as a pro mechanic, and don't have a particularly huge penis, I won't divulge how I will obtain the proper chain length. Besides, it's actually for my wife's bike because a guy with my skills and experience would never admit to needing a 34/28 low gear. :banana:

[RPS]

The thread on chain length got me wondering if anybody has tried the new shimano 11-28 cassette with 50/34 chain rings and a shimano short cage derrailleur. I am currently using a 12-27 50/34 combo which exceeds the wrap capacity of a short cage derrailleur, but works fine. Am I asking for trouble by pushing it to an 11-28 cassette and further exceeding suggested capacity?
The previous generation of Dura-Ace and Ultegra had a capacity of 29T which your present setup exceeds since you need 31 teeth of total capacity. As others have stated and you confirmed if the chainstays are just the right length it's fine to exceed the capacity by a little amount.

The newest DA and Ultegra short cage derailleurs are now rated at 33T for the short cage and 39T for the long cage meant for triple applications. The new Ultegra and DA derailleurs with 33 teeth of capacity are meant to handle your 50-34 along with a 28-11 cassette (16+17=33).

Do you know which model rear derailleur you have?

[RPS]

The der. is a 7800 That one has a listed 29 teeth of capacity.

[AndrewS]

You can exceed your derailleur capacity without the world ending. But you need to choose where you're going to have the limit be - low end slack or high end overtension (or a little of both).

Low end is obviously the safer choice, but if you trust yourself not to shift willy-nilly, you may get better performance making the Big/Big crossover off limits.


I don't really see how the chainstay length is particularly relevant, aside from being one of several factors determining if the sweet spot for chain length falls right on or a half link off. Neither should prevent this set up from working.

My mountain bike has a 12-28 with a 42x32x22 triple and a 28t capacity Ultegra RD that has been going fine for 14 years. I think you'll be just fine.

[AndrewS]

Also, if you are having a problem with the 28 tooth cog rubbing, a slightly shorter chain with a Shimano derailleur can sometimes help create more clearance than just using the B tension by itself. YMMV

[RPS]

I don't really see how the chainstay length is particularly relevant, aside from being one of several factors determining if the sweet spot for chain length falls right on or a half link off. Neither should prevent this set up from working.

It’s only relevant as it affects total rear derailleur capacity. Whether it works or not depends on your definition of “work” and I’m not going to argue that with you. I already know your view on that so there is no point discussing it further.

Regarding capacity: I trust that when Shimano rates a rear derailleur capacity they do so without assuming the owner will use a chain half link to get maximum capacity based on variations in chainstay lengths. That being the case, it is reasonable to assume their rear derailleurs are rated based on the chain sometimes being “just” barely a little longer than it could be and still work without rubbing. That requires an additional entire inch of chain to be cut off.

If I work those numbers backwards I conclude that the RD capacity can vary up to 3 teeth greater than specified based on the chainstay length if one is lucky. That’s why it is very shortsighted for anyone to follow someone else’s recommendation when they say that they have used a certain combination and it works great. It may work great on bike “A” but may not work the same on bike “B”.

Again, my assumption is based on the fact that if they rate a rear derailleur at 33 teeth of capacity that they mean it will have at least 33 teeth of capacity on “ANY” bike. By my way of looking at this issue sometimes it will be possible to obtain up to 36 teeth of capacity based on being lucky with chainstay length.

I could be wrong and Shimano may rate them on average or some other criteria, but it is interesting that I’ve never seen a single person say they couldn’t at least get the rating out of a derailleur. If there is a reported deviation in capacity it’s always to the upside. That being the case my assumption seems reasonable.

[RPS]

P.S. – To be clear and avoid fireworks, I’m not suggesting that’s the only factor that affects total rear capacity. Even if we compare two identical frames with identical derailleurs there can still be a difference in actual total capacity based on sizes of chainrings and cogs. The sizes of the rings and cogs selected (and thus compared) can have the same effect as chainstay length differences.

[oldpotatoe]

The thread on chain length got me wondering if anybody has tried the new shimano 11-28 cassette with 50/34 chain rings and a shimano short cage derrailleur. I am currently using a 12-27 50/34 combo which exceeds the wrap capacity of a short cage derrailleur, but works fine. Am I asking for trouble by pushing it to an 11-28 cassette and further exceeding suggested capacity?

No. I just installed this on a Ultegra group and shimano's 11-28 10s cogset..works just fine. ''Limits' of shimano's RD are VERY conservative. I have used a 12-30/9s w/o problem as well.

[AndrewS]

RPS,

That seems entirely reasonable to me. I would also like to think that the stated capacity is a minimum rather than best case. I imagine hanger location would have as much or more effect, but simply calling the problem "chainstay length" does get the point across, so there's nothing to quibble about.

Thanks for clarifying.

[Dave]

You can exceed your derailleur capacity without the world ending. But you need to choose where you're going to have the limit be - low end slack or high end overtension (or a little of both).

Low end is obviously the safer choice, but if you trust yourself not to shift willy-nilly, you may get better performance making the Big/Big crossover off limits.


I don't really see how the chainstay length is particularly relevant, aside from being one of several factors determining if the sweet spot for chain length falls right on or a half link off. Neither should prevent this set up from working.

My mountain bike has a 12-28 with a 42x32x22 triple and a 28t capacity Ultegra RD that has been going fine for 14 years. I think you'll be just fine.


Nothing personal, but your ignorance is showing again. The minimum chain length change is 1 inch and that equals 4 cog teeth. If you change from a 12-27 to a 11-28 it will increase the chain tension slightly in the big/big and reduce it in the little/little with no change to the chain length. You can't just decide to have a little bit of a problem at either end of the cassette. It might work out that way in some cases, but not all. If the chain length is increased by 1 inch, you get enough length to handle another 4T and the chain will almost certainly be too loose in the little/little.

If you can't see how chain stay length is relevant, you're not well versed in this subject. The worst case chainstay length will create 2T less wrap capacity than the best case. That's why different bikes with the same cog and chainring setup won't have the same tension at both extremes.

You can find examples of the "rigorous" chain length formula at several websites. Park Tool has the formula shown on their website. You MUST have the chainstay length to use the formula. What you want is a chainstay length that requires a chain length that is as close as possible to a length in even inches, like 52, 53, 54. A chainstay length that requires a chain length ending with .5 inch is the worst case.

All RDs should have at least 2T more wrap capacity than officially stated amount, to handle the worst case chainstay length. Those who have the perfect length just get a little more wrap, 2T maximum.

[AndrewS]

Dave, nothing personal, but you can drop the insulting tone that accompanies your every post. Why don't you take a look at the forum rules and stop acting like a teenager. It was tiresome the first time, and it only continues to be a juvenile diversion from having nice discussions about bicycles. There is simply no reason for you to insult me or any other forum members - especially just to stroke your own ego.

If you can't make a salient point without undercutting the opposing viewpoint with irrelevant distracters, your point is probably not worth making.

As I stated in the post that you quoted, it didn't seem "particularly relevant". In English, this means that it is relevant, but probably of little consequence or overall effect.

Why? Because the OP already has a 12-27 that's working fine. 11-28 is also likely to work.

I have never, never seen an instance where selecting a chain length caused the problems you seem to be hinting at. Even at slightly overcapacity, you still have a choice of 1 inch increments between slightly too little and too much, which is more than sufficient. You can choose to center the capacity closer to the Big/Big side or, as you gave an example of with short cage triples for ATBs, small/small. Or, as I said, split the difference.

There's nothing magical about this. Worrying about the effect of chainstay length and referencing formulas just distracts from the simple fact that you hook up the chain and see how it fits in a couple different gear combinations. It doesn't require any more planning than knowing where you might encounter problems and having a general idea of the overall results of adding or subtracting an inch of chain will do. Stop complicating something so simple.

[Dave]

I just posted the fact that chainstay length is why certain extreme combinations work on some bikes and not on others. It also makes a bike have the perfect chainstay length with some combinations and not others, so you can change to a setup that reduces your maxium wrap capacity. Your post seemd to claim that not to be true or not worth consideration.

When people post that a certain combination that shouldn't work does, there is a reason for it most often, it's that 2T of extra wrap capacity that some frames have and others don't. This can mislead people into thinking that if it works on one bike, it should work on all.

[Tobias]

All RDs should have at least 2T more wrap capacity than officially stated amount, to handle the worst case chainstay length. Those who have the perfect length just get a little more wrap, 2T maximum.
When people post that a certain combination that shouldn't work does, there is a reason for it most often, it's that 2T of extra wrap capacity that some frames have and others don't. This can mislead people into thinking that if it works on one bike, it should work on all.
Why do you differ from Rick who stated that "up to" 3T is possible in some cases?

I can follow his logic, but don't know where you get 2T?

Not trying to start a pissing contest, just want to know the basis of 2 versus 3. :confused:

[Dave]

I thinks that RPS is correct. For example, if the formula suggests a minimum length of 53.25 inches, you should have to use a 54 inch length to wrap the big/big and that is 3T more length than needed. That also means that RDs must have at least 3T more wrap capacity than stated to handle this worst case. I have no idea if manufacturers really design it this close, or throw in another 1T just to be safe.

http://www.machinehead-software.co.uk/bike/chain_length/bicycle_derailleur_alowances.html

http://www.pvdwiki.com/index.php?title=Chain_Length_Calculation

You never know for sure what the true maximum wrap of a RD really is until you try it - I agree with Andrew about that. Campy used to rate their RDs to have a maximum wrap that equalled whatever range of cogs and chainrings they sold. When compacts first came out, that max wrap went up by 2T, but the cage length did not get any longer. That means there was at least 5T more wrap available than advertised.

A current short cage Campy 11 RD has a cage length of 55mm (center to center between the pulleys). I think that's been the same for a long time, but I don't have an old one to measure. All I've got is a medium cage (72mm). The wrap keeps increasing so now it's up to 33T (50/34 with a 12-29). That did require a change to the B-screw mechanism to clear the 29T cog, so 2009 RDs are not the the same as 2010.

The wrap used to be advertised as 27T when it was recommended for use with a 53/39 and up to a 13-26. The fact that it was not recommended for a 13-29 may have been strictly due to large cog clearance and not the lack of wrap.

[AndrewS]

Dave,

I understand what you are saying about the chainstay length, but in the real world there is no application for that knowledge. That's because chain stay length is only one of several factors that ultimately impact on usable capacity. The others are cog diameter, derailleur hanger location, b tension adjustment and geometry of the derailleur. That's ignoring horizontal dropouts.

RD capacity is likely a minimum the consumer can count on. The above factors can certainly help or hinder, but they can't all be accounted for on paper without extensive testing, which no one has done. And it still would be halphazard.

In the real world, you set the chain up properly for the gearing, and try it. You may get all the capacity you were hoping for (I get 30 out of my 28 Ultegra on my ATB), or you might only get the stated capacity.

But even if you are technically over capacity, the drivetrain is still totally serviceable, as long as the rider understands its limitations (which are usually just the crossover gears no one should be using anyway). Which is why I suggest they make their own choices when it comes to going overcapacity. In this case, I would set things up around the center of capacity and avoid the two crossovers. But the OP may have different shifting tendencies than I do, so he needs to center the capacity where he'll use it.

You can analyze this kind of thing until the cows come home, but the correct answer takes 5 minutes and a chain tool. No tape measures or slide rules necessary.

[Dave]

Andrew,

Glad you understand the chainstay thing. Apparently you didn't before.

What it points out is that a setup may work fine on one bike, but that same setup will not work on another, entirely due to chainstay length differences and nothing else. You can't rely on someone posting that a setup works fine on their bike unless you know what chainstay length they have. If you know that, then the information may truly be of value.

One of these setups that pushes the limits can't always be swapped over to another frame that a user purchases. You might get unlucky and lose 3T of wrap. I can see it now. "Gee it worked fine on my other frame, why not this one? Everything is the same."

A chain length calculator would at least predict such a problem.

[AndrewS]

No, I "apparently" did understand the chainstay thing. I felt it was a non-problem, and still do, because it is not the only factor.

Even with identical chainstays, it still might not work because of the other factors I listed.

Using a chainstay calculator can certainly help talk yourself out of something, but if you're already pushing capacity you should be prepared for limitations on the drivetrain; not disappointed when it functions as advertised by the RD maker.

The technical, correct answer to the OPs question is "No, Shimano says it won't work". The real answer is "It depends on a number of factors and your willingness to not use certain combinations". Anything else is fooey. And if I heard a mechanic telling a customer that he was going to "measure their chainstays" before a build I'd find a different mechanic to deal with.

You can get a result from the chainstay formula that will tell you that it won't work by 2 teeth. Then you can build it and find that the derailleur, cogs, hangar and whatever else make it work BETTER than the bike with the ideal chainstay length. That is what you don't seem to be getting from my posts.

[Dave]

What part of "same setup" don't you understand? Same setup means all the other factors you listed are the same. That leaves only the chainstay length as far as wrap capacity is concerned. The RD hanger geometry can affect largest cog clearance.

I agree though, that putting the thing together is the way to prove that something works. That's what I do, but the most I've ever exceeded wrap capacity is 2T, using a 53/39/28 crank with a Campy medium cage RD having a rated 36T wrap capacity.

[AndrewS]

"Same setup" means different things to different people. It might mean the same total capacity gearing, it might mean the exact same gearing but using a different brand or model derailleur of the same capacity, or it might mean the same everything down to the frame. I don't know.

But even if it's every component down to the lockring and cable end, the hanger length and location is more than enough to screw with any sort of tabulation based on chainstays.

I measured the chainstays of 3 quality 51 cm road bicycles from 3 different brands. They all have "race" geometry, but are definitely different. Yet the chainstays were all within 8mm. I measured the hangers on 5 different bicycles and got a variance of 5mms. I didn't bother to measure the hanger angle, but those looked like they varied by 5 to 10 degrees.

Please tell me how you plan to get accurate information given the variances I've stated above? Each hanger may add or subtract from the chainstay length issue, but you won't know it until you try it. Garbage in, garbage out.


I really wish that the people at Park Tool would be a little more circumspect about what they put on their site. Last time someone referenced Park they wanted to Loctite their BB cups because Park said to.

[dave thompson]

Much simpler explanation here: http://forums.thepaceline.net/showpost.php?p=756952&postcount=5 :)

[AndrewS]

Mr. Thompson, it's a wonder no one called you ignorant.

[Dave]

http://i47.tinypic.com/2d0anas.jpg