I've seen conflicting methods for determining chain length, for example:


Small cog to small ring:

https://www.youtube.com/watch?v=WnRxNHkRh8Q



Small cog to big ring:

https://www.youtube.com/watch?v=erL6Y6JFfnA


Big cog to big ring:

https://www.youtube.com/watch?v=OBv97hqqd0o


On SheldonBrown.com he promotes the big to big technique:

"The best technique for setting chain length is to thread the chain onto the large/large combination, without running it through the rear derailer. Mesh the two ends on to the large chainwheel so that one complete link (one inch, -- one inner and one outer half-link) overlaps. In almost all cases, this will give the optimum length."

Derailer Adjustment

So....

Which is correct, or better, and why?

Thank you.


P.S. This is for my road bike, double rings up front, 11-25 cassette, DA short cage RD.

I usually use the small-small method, except when I use big-big, unless I just match the old chain.

I always use the small to small method .

I've said this so often it's like a Mantra.

There are 3 chain lengths.

1- the Minimum - found by the big/big +1" method (note: this is an absolute minimum method with no fudge room.
2- the Maximum - found by the small/small & take up slack method. This has some fudge room if wide range gearing exceeds RD take up capacity.
3- Correct length - anything between the minimum and maximum, according to RD cage orientation, or your preference.

I run chains near the maximum because it leaves me room to change to a larger cassette or remove damaged links if I ever need to. While some people run minimum length and carry spare links, my spares are already in the chain.

IMPORTANT -- the minimum is an absolute non-fudgeable length, so unless you're sure your gear combination is within RD capacity, measure the minimum and confirm that your length is longer. Or if confident, shift into big/big (slowly) after cutting to confirm.

BTW- if setting up a race bike always use the maximum method. The few grams of added weight are well worth it because it allows you to use a donated or neutral support wheel in a race without worry about the cassette size.

I once watched a rider with a corn cob cassette grab a donated wheel after flatting, and destroy his drivetrain at the first hill when he shifted to a sprocket too large and ran out of chain.

Using the big/big method will yield the shortest chain that is safe to use with your gear combinations.

Using the small/small will yield the longest chain that your derailleur can handle the slack.

Anything between those two extremes is OK by me.

Thank you! I usually, sometimes, use the small to medium if I'm using a mid compact crank, except on Tuesdays, or when it might rain, or if there are Seinfeld re-runs are on, then I just switch the bike to direct drive.

Great tip, that's so important. Especially keeping in mind that I'm going to pick up a 11-27 or 11-28 for mountain training to switch on when needed.

Thank you.

I've heard the clink-tink and felt the non-restiance of a broken chain. It's nice to know you can just take off links to be able to put it back together and continue your ride.

Thanks, will follow this and the previous post from FBinNY; sounds like you both are the same track and have serious experience with this.

New chains , err to the long side , you can shorten a chain, but the way they are made now

you cannot add links without using another Quick link.

Shimano and SRAM generally recommend threading the chain from the big ring to smallest cog going through the RD, then just join the chain exactly at the measurement that makes the line through the two RD jockey wheels as close to vertical as possible. This method is not much recommended by the knowledgeable folks here, and they cite good reasons for their rejection of this method such as little forgiveness for a bigger cassette. Nevertheless I have always used it successfully and do occasionally use my big-big combination (53/26). I tend to also check the chain length on the small front to big rear combination which in my case is one tooth larger 26 + 39 = 65 vs. 11 + 53 = 64. Different strokes for different folks.

Any of a number of methods will work fine when operating within the capacity of the RD, where there's a working range between the minimum and maximum length.

However issues can occur when running at or slightly over RD capacity, where chain length can become critical with little or no room for error. That's when checking the minimum length becomes important.

Fully agreed. I was really just saying how you get into a habit, in this case the manufacturer's recommendation for the parts I have always used, and it can be tough to switch. Even in the face of good advice. As I understand it, Campy has a different recommendation; isn't it more like your preferred method?

Thanks guys, very helpful.

I guess I was asking for a standard which really doesn't exist.

I'll follow conservative suggestions and can always take an extra link out if needed.

Yes, this is one of the cases that shows the difference between teaching and doing. When working on my own bikes, or bikes in my hands, I don't bother with minimum length. I confirm that the gear range is within capacity by mental arithmetic, and go straight to my longest chain method, or one similar to yours. I finish by checking my work (in case I couldn't add, or spaced out) by shifting to bib/big, then I'm done.

However, when teaching, I have to cover bases, and suggest confirming the minimum length, because I don't know if the person understands capacity, or has some super wide gearing, or even simply a super wide cassette where the small/small method can leave him short.

It's like giving driving directions. Folks often give the worst directions in areas they're most familiar with because they use subconscious landmarks, which they can't or simply forget to explain. For instance is the turn 5 or 6 lights down the road, do you know, or do you just recognize the right place when you get there.

That's a big qualifier. Many riders (me, for example) using triple road cranks will change the factory 30T granny chainring for a 26 or even 24T. That change will usually exceed the derailleur's published wrap capacity so using small-small may leave the chain too short to cover the absolutely essential big-big.

Good point.

There's also this: One generally only uses the granny chainring combined with the largest 2 or 3 rear cogs for grinding up steep hills. Consequently many riders never use their derailleurs full slack take up capability. Also, if the chain does go a little slack in the little/little, what's the worst that's likely to happen?

If I'm going to err, I want a chain that's a little too long rather than a little too short.

Which is why, I suggest double checking the big/big combination to ensure that you're cutting longer than the minimum. Read Post 4 which is my whole answer, especially the phrase following the bold face IMPORTANT..

Those aren't necessarily opposite- depending on the gearing, there can be small small situations that don't allow enough chain for big big. 52-42-24 triple to a 12-28 can happen easily enough (only one granny gear and a cassette swap away for most bikes), tough to know off the top of your head if the RD is up for the task.

Me? Big big, because a chain too short make for MUCH more serious problems than a chain whose slack can't entirely be taken up. I want to KNOW for sure that a being caught off guard by a hill doesn't have me risking my RD, wheel and frame.

E: basically what's already been said.

I think it's clearer if we separate the issues of method from the results.

We all agree that anything between the minimum and maximum (or a fudge version of the maximum) is OK.

As for method, the big/big method is safest because it ensures a chain above minimum. However, nothing says this is the best length. As posted, there are advantages to a longer chain, and the small/small method works fine AS LONG AS you're working within RD capacity.

So for newbies, they should start with big/big and note the maximum number of links they can cut, then use the small/small method to decide how many of those they'll actually cut.

As a rule, those running at or above RD capacity will use the minimum length. Those with capacity to spare, may prefer going longer.

I'm on board, but I think use of the word 'maximum' to define the length of a chain is dangerous. It's a method that works fine 99.9%, but when it doesn't, he results are disastrous (and expensive), and its most decidedly NOT a 'maximum' length. To me maximum implies that all the other bases are covered, not that there's still a risk of ripping the hanger off your frame.

I've noticed a lot of bicycle mechanics subforum users are recent purchasers of used bikes with unknown modifications to gearing, I fear the subtlety of your bolded caveat might be over the heads of members that actually need advice.

If it's a methodology we're chasing here, something on the order of a checklist/flowchart might be better. I feel the min/max terminology undermines the huge disparity in consequence. There needs to be a paramount priority on big big working as a gear choice, no matter what other criteria exist.

I.E.

do you have the old chain?
Y: match that length with new chain

N: see if big-big works

...

Try small small

...


If small small has flopping issues, take out as many links as you can, while keeping big big working.

There are many ways to skin a cat. I'm pretty consistent in reminding people that the minimum is an absolute minimum, while the maximum can be fudged if running systems over rated capacity.

OTOH, the manufacturers are clear about capacity ratings, so folks treading in the over cap. never-never land where the max, is less than the min. need to understand the real estate and act accordingly.

BTW- this doesn't even broach the question of those who diligently cut a chain to a safe minimum length, then swap wheels to one with a larger cassette and destroy the bike.

There's no way to ensure a best result for every situation, and folks need to know WTF they're doing, or accept that they're living in a minefield.

Seems that it might be a good idea to keep a spare, pre-sized longer chain with my larger cassette. Whenever I swap to the larger cassette, I'd swap chains at the same time. That way, I'd not be continually in a compromise situation.

Chains aren't that expensive, so no reason I can think of not to do this..

Sound like a decent approach?

Btw, if anyone has a standard Shimano crank setup (53-39) and runs a 11-25 cassette...out of curiosity, how many links are in the chain you're running now?

No, it's not a sensible approach because there's no reason to. The chain sized for the larger cassette can always be used with the smaller one, since both cassettes likely use a similar sized smallest sprocket. So, once you have the chain long enough for the larger cassette there's no reason to switch back.

As to what others use, it's not relevant because they may have longer or shorter chainstays. Here's some good advice about dangers of basing your bike on what others do.