Chain Length for Two Different Cassettes
 

I currently have an 11-28 and am getting a new 11-23 and chain. I'm holding onto the 11-28 on a different set of wheels as a backup set or for when I ride hills I can't do on an 11-23.

If I size the new chain for the new 11-23 cassette (using the Park big-big +2 method) will it be too short for the 11-28? Is there a happy medium? Or do I have to size for the largest?

I would just size it for the 11-28 and then the 11-23 will be no problem.

It may end up a bit longer than you'd size for only the 11-23 but there shouldn't be any significant functional differences.

There is no reason to shorten the chain from the length required to use the 11-28. It will be too short for the 11-28, if resized for the 11-23, since 4 teeth of wrap is 1 inch. Five teeth smaller might suggest a 2 inch shorter chain.

Ther will be no change in performance, using the longer chain length.

Rather than using the big/big plus 1 inch method, try the little/little method. Shift to the little ring and smallest or next to smallest cog. The chain should be as long as possible without hanging loose. As long as the lower end of the cage moves forward and creates some tension on the chain, then it's not too long.

Are you kidding? Weight weenies will tell you all those extra links will make you spin up like you're riding in cold porridge! :eek:

OP, I swap 23 to 28 often, no problems. :thumb:

+1

With the same small-small combo your max chain length is the same. Unless your derailleur is not capable of handling the 11-28 and whatever chainring difference you have things will be fine.

I size all my chains this way. A longer chain may bounce a bit more when using the small chainring and smaller cogs but it has a lot less friction in the big chainring and bigger cogs.

Thanks for the feedback.

Will this result in a different length? Longer or shorter? If so, what's the theory? If it's not loose then the chain will be long enough up to the largest cog that will work with the derailleur?

Yes, it will be longer because you're providing the max length chain your RD can handle rather than the minimum length to allow a big/big combo. The small/small method allows you not to worry about chain length if you pop on a larger cassette.

I personally prefer the big/big method of sizing because you absolutely know the length is there plus you don't have more than you need. But if you use that method and don't use a different chain for each cassette, you must size for your largest cassette.

The little/little method makes the chain as long as possible and provides the maximum wrap capacity. If you were to install a cassette with a largest cog that exceeds the manufacturer's recommendation for the max. cog size and wrap capacity, it would not be long enough. In that case, the big/big method would be safer, but the chain would also hang loose when the chain's on the little ring and several of the smallest cogs.

With a Campy 11 drivetrain, there is one chain length that will handle any cassette that Campy offers. There's no need to make the chain any shorter.

Small/Small is by far my personal preference. It pretty much assures you that you can run anyone's wheel or cassette. Example - at yesterday's races I moved around near 10-15 different wheels between bikes. All with different cassettes, etc. No worries. Big-Big is fine if you're only ever using your own equipment and never plan on changing your gearing.

I've always used the large/large method...not running it through the derailleur and adding a few links before cutting.

Just so I'm clear, the small/small DOES run through the derailleur and you take out enough links so that the derailleur has tension, right?

Yes. As long as the lower end of the cage moves forward when the ends of the chain are brought together and the chain doesn't rub either on itself or an upper chain guide on the cage, then the chain is short enough.

When using the big/big method, two links (1 inch) are added, unless the ends that come together are the same. In that case, add three links to get one pair of inner plates and one pair of outer plates to join.

Depending on the chain stay length and the chainring/cog combination being used, there are times when an extra inch of chain is needed, just to gain 1/4 inch for one tooth of additional capacity. That's also why some combinations that exceed the manufacturer's maximum will work on some frames and not others. If you happen to have the perfect chainstay length it will work. Some other frame could have 3T less wrap capacity.

I think I'll try both methods and see how much difference there is. Will size the 28 cog so that I can use it, but curious if the small-small results in an even longer chain. I see no reason to have a chain longer than what's needed for a safe big-big combo.

My guess is that it will be the same. I've heard that the chain wrap capacity of the 6700 was increased specifically so people could run an 11-28 with a compact crank. The rated chain wrap of 6600 was less than the 33T of running an 11/28 with a 50/34 (but people did it successfully anyway)

Find a rider that uses the small-small set up. Find another rider with the same large chainring and large cog that uses the big-big method.

Put it in the big-big. Lift the rear wheel off the ground. Turn the pedals. There's a lot of friction in the big-big when using the shorter chain setup.

It also works if you do the small-small method on your own bike then the big-big, but then you'll want to go to the small-small and you'll have to lengthen the chain.

psimet also makes a good point. It's one of those safety habit things. You always wear a helmet or seatbelt when you ride or drive. You don't plan on crashing either vehicle when you start off (unless you're committing suicide, murder, or you are a stunt person), but you still do it. Using the small-small method is very safe and eliminates accidental wheel popping out (or worse) when you inadvertently use a wheel with a larger large cog (heck, the second cog may be bigger than your current big cog).

The extra chain wrap you get when you use the small-small method also gives you quicker and/or more precise shifting in the rear. The chain has less distance to span between the pulley and the rear cog. Before all derailleurs had similar geometry this was the way to get less-functional derailleurs to work well (or well enough).

The only disadvantage to the small-small method is that the chain bounces more in the small ring and smaller cogs due to lower chain tension (a result of longer chain and a relatively light spring in the rear derailleur). If it's a big issue you can just put it in the big ring - that's an acknowledged way of dealing with rough terrain, using the big chainring to increase chain tension.

This method is only safe if you're sure that the rear derailleur you're using has a wrap capacity that's sufficient for your rings and cassettes. That's true on most bikes, but on one of mine the crankset was changed to one with wider spacing and the derailleur wrap capacity is no longer sufficient.

If I put on a chain using the small-small method it'll end up too short if the bike is shifted to the large-large combination. There would be the danger of the chain jamming and damaging the bike or possibly causing a crash. Using the large-large method of sizing the chain on this bike results in a longer chain but one that will have significant slack if the bike is ever shifted to one of the smallest cogs when on the small inner chain ring. Not ideal but not something that causes any harm. Since the inner chain ring on this bike is only used as a bail-out granny gear on very steep climbs it is only used in combination with the larger cogs on the cassette and in that case there's plenty of chain tension.

So on that bike the small-small method is not at all a safe one to use and I always size the chain using the large-large combination instead.

My current setup was done that way (big-big). Never noticed any extra friction but then I guess I don't have anything to compare too. However, using big-big resulted in the exact same length as the stock chain. I just checked though and in small-small the two pulleys are "nearly" horizontal with just a bit of tension. Pretty much what I would have expected had I used the small-small method. Probably because with a 28 the chain will be close to max length for the derailleur as that's the biggest recommended cog.

I currently have an 11-28 on the bike. Moving to 11-23 would result in a shorter chain using the big-big method but probably the same length using the small-small since both use an 11. Obviously the big-bib method won't work if I size it for the 23 when I try to put in a wheel with a 28. However, I wasn't planning to do that. Sounds like I'm going to end up with the same length chain again.

that's so incorrect that it's sad. You either don't know what youre doing or you are completely running incompatible setups. Small small results in the absolute LONGEST chain that you can run on that bike. If it results in a chain that is too short in the big big then you are running a combo that is outside of feasible wrap. Period. If you then size it big big then you're going to throw your chain when nailing it after the top of a climb and can't see straight.

Just put the chain tool down and step back from the bike. Just because it's a simple machine doesn't mean that everyone has common sense.

Then I suggest that you take an elementary school reading course since I clearly stated that on that bike the rear derailleur has insufficient chain wrap capacity for the current rings and cogs - so yes, it's obviously 'outside of feasible wrap'. [Getting the gear range I wanted for the wheel size on that bike required going outside the wrap capacity of available derailleurs.]

Given that condition then there will either be a loose chain in the small-small combination (if the chain is sized using large-large) or a chain that's too short to go into the large-large combination (if the chain is sized small-small). The latter is far more likely to cause serious problems so on that bike it's better to use large-large for sizing the chain and live with the fact that the chain will be loose if I ever accidentally shift into the smallest cogs while still on the 'granny' smallest chain ring.

So, as I said before, chain sizing using small-small is safe if (and only if) one is sure that the rear derailleur has sufficient chain wrap capacity for the rings and cogs that will be used.

I think you missed the fundamental point - riding a setup with more gear range than chain wrap capacity is not only extremely dangerous but reeks of shade tree, amateurish mechanical work. Not only is it just a poor execution but should never be done in any way shape or form. Providing advice on this forum that recommends how to attempt to use such a setup is irresponsible at best and a liability for sure.

Just because you do it doesn't mean anyone else should ever follow your advice.

Interesting information in this thread.

I've just always done big/big. When I get a new cassette, I size and marry a chain to it. When I swap cassettes, it's dedicated chain goes on the bike with it.

Is there any other advantage to small/small besides being able to use different cassettes?

It will tend to run and shift better. Also it's not just "I can swap cassettes" It's more - "hey if I accidentally put a cassette on that is larger than my current one I won't detonate my rear derail."

This would be a bizarre accident...

I used to run long chains, but now I run short ones. Friction may be an issue in big ring big cog combos, but if you're up against sufficient wind or hills to put you there, you've selected the wrong ring. I also like to keep cassettes and chains together.

Yes - for a person running only their own gear and with only say - 1 set of wheels and limited cassettes. With lots of riders and lots of wheels - it's actually really easy to do. I have had racers who sized their setups for 11-23 cassettes who made their chains as short as they could with those setups - only to grab a wheel from someone with a 12-27 cassette. Derail go boom.

They don't stop and ask questions about gearing in a race...

And you clearly missed mine. The advice given before was that using the small-small method is *always* the safe way to go - and this was made without any qualifications. That's fine *as long as* the person using it is sure that the rear derailleur has sufficient wrap capacity for the chain rings and cogs that will be used.

Someone reading the previous advice that this method is always safe and therefore using it on a bike where there is insufficient wrap capacity could be in for a very unpleasant surprise if there's an attempt to shift into the large-large combination.

My advice was not to deliberately design a drive train with insufficient wrap capacity, but that one should be sure it is sufficient before relying on the small-small method of chain sizing.

I'd note that this is consistent with Sheldon Brown's advice in:
http://sheldonbrown.com/derailer-adjustment.html#chain
"If the chain is too short, it will be at risk for jamming and possibly ruining the rear derailer if you accidentally shift into the large-large combination. Never run with a chain that is too short, except in an emergency.
If the chain is too long, it will hang slack in the small-small combinations. You should never use those combinations anyway, so this is not a serious problem. If you exceed the recommended gear range for a particular rear derailer, you may have to accept droop in these gears.
The best technique for setting chain length is to thread the chain onto the large/large combination ..."

Of course if one will be using a variety of cassettes then the large-large method needs to be applied with the cassette having the largest cog.

I think that counts as a qualification. You repeat it, and you're right.