Chain length calculator?
 

In buying a new chain, but I cant remember how long it should be.

Bike has 415 mm chain stays, 50/34 crank and 12-28 cassette. Im guessing 116 links is enough, but am I right?

This calculator says 106 links, but is it trust worthy?

Chain length calculator

116 links is plenty. Never used a chain length calculator.

You do not say if you still have the have the old chain? Lay the two of them down flat fully extended make the length of the new same as the old. I have used the calculator on parktools.com/chainlength and have no problems with it.

That makes the assumption that the current chain is sized properly. There is no guarantee it is.

​​​​​​Your gearing is very conventional so you will have more than enough length with a standard 114 to 116 link new chain. You will want to remove the extra length and the recommended sizing technique is to wrap the chain around the large chainring and the largest cog simultaneously (don't route it through the rear derailleur) and add 1" (2 half-links) and cut it to that length. That will assure you can safely shift into big-big. Be sure to properly match the ends (one male and one female if using a joining pin or male at both ends if using a quick link) and round up if needed to get a match.

Parktool's formula
Simple Equation: L = 2 (C) + (F/4 + R/4 + 1)

L = Chain length in inches. Round the final result to closest whole inch figure. C = Chain stay length in inches, measure to closest 1/8". Use chart above to find decimal measurement. F= Number of teeth on largest front chainring. R= Number of teeth on largest rear cog.

Some things are done better using analogue methods.

1. Wrap your chain around the biggest chainring and biggest rear sprocket bypassing the derailleur.
2. Figure out the shortest place you would be able to rejoin the chain.
3. Add 1" of chain (1 wide link and 1 shirt link) to that amount.

This is the correct method. Big /big +1" of chain overlap. Super easy and no math work required.

this

easy peasy, and as already mentioned, avoids any problems if your old chain was too short and you never knew.

Obviously this system works and not disputing.. but why is it that in my head I'm imagining that after running the chain thru the RD, it would take up more than the extra 1" that was added at the end of this process?

I've puzzled over the same thing, and it's counter-intuitive, but that extra inch is actually a lot of chain droop, so it's plenty to accommodate the derailleur.

You forgot to factor the variable of a long or short cage DR
Javascript Bicycle Chain Length Calculator

I have to imagine there are some things though that could affect this formula -- GS vs standard RD? CeramicSpeed pulleys?

Big/big plus one inch is fine if you're using the biggest sprocket that you every plan to run. If you set the chain length with a 28T and later change to a 32 or 34, then the chain will be too short. The longer length will work with any of those sizes, unless you're deliberately exceeding the RD's wrap capacity.

To get that length, use the little/little and make the chain as long as possible without hanging loose. As long as the RD moves forward by a small amount when the ends are joined, you have the length needed for any cassette within the RD's wrap capacity.

If you're deliberately exceeding the RD's wrap capacity, then the big/big plus 1 inch will give a chain length that will hang loose in several of the smaller cogs.

FWIW, I've used the same chain length on all of my road bikes, with largest cogs from 25-32T and 53/39, 53/39/28 or 50/34 cranks. Of course, all setups are within the RD's wrap capacity.

If you look at the rear derailleur you will see it is stretched into a straight line when the chain is completely tight so it adds nothing to the required chain length. The extra 1" gives enough chain length for the chain to climb over the chainring and cog teeth during a shift. This is critical if you shift into big-big.

I test with the chain on the bike and a C bent piece of old spoke with chain on big big combo and running thru the RD.

then cut the chain and fit quick link ..

save the removed section and get a spare quick link for potential chain breaks..

Park Tools, the best and largest bike tool company, they make a whole slew of well made, reliable information videos on bike mechanic stuff--you can trust them

chain length video--hard and EASY way, go with the easy way, its easy.
Mr Parks video guy wouldnt tell you if it wasnt true folks.

I've never used calculations. I take the new, uncut chain and wrap it around the bib-big and through the RD pulleys. Not the link at which the chain isn't fully tight. move the chain to small-small and observe if that will be ridable. (On many newer bikes, small-small isn't ridable anyway; chain pickup by the large chainring.)

In my eyes, a ridable big-big is a necessity, not a luxury. Chain slack and/or chain dragging on itself in small-small is OK. I never plan to spend time in the big-big but the fiasco of that combination of being too tight and getting used by mistake by a very tired rider after a long climb - well I don't like ride enders, big money repairs, damaged frames or doing the call of shame. Noisy small-smalls have never caused me an issue and I've been setting up triples that way for 40 years.

Ben

Thanks guys. I know how to size it, if its long enough to begin with. Just couldnt remember how long it needs to be and if 116 links is enough. Seems 116 links is more than plenty. According to various calculators it should be 106-108 links, in line with your replys. Thanks again.

When the chain is on on the big/big the derailleur arm is pulled almost horizontal. Both runs of the chain are nearly a straight line.

and I would assume it helps cuz its less screwing around putting the chain through the pulleys only to be taken out again for you to remove links, thus saves time.

This method is what I had been told to use as well. Seems to be working out fine for me. Some of my chains were way too long / slacky.

Yes, but if you later change to a larger cog cassette it is very likely you will change the chain along with the new cassette so you will adjust the new chain to match. I suppose there are riders with multiple wheels with different cassettes for different riding conditions and they would have to size the chain for the largest one.

Staying within the derailleurs wrap capacity is the requirement for sizing small-small. I often exceed it by changing the granny chainring on triple cranks for a smaller one than OEM and I always size for big-big. Yes the chain will be slack in the smallest cog or two when in the granny chainring but that's easy to avoid and only a nuisance if you attempt to use it. Yes, I've heard the argument that the slack chain could fall off and mangle things but I've never heard of it actually happening and can't see it as a problem unless the chain is VERY slack. That doesn't happen.

exactly my experience, going back to 1991
changed my granny from 28t to 24t. Chain sized for 50/40/28 and 13-30.
with the change to a 24t, yes in the 24t-13cog position the chain touches the pulley a bit, but not a problem, just an audio reminder to not be in small-small, BUT the chain was at a safe length for big-big (both of which I really never do, probably only a handful of times over the years)

I have used the calculators twice, and they were spot on.

That's my philosophy too. I've only ever used my granny chainring for climbing steep hills in the biggest 2 or 3 rear cogs. As soon as I crest the hill, I shift back to the middle or big chainring. I wouldn't do it on a customer bike but I stopped worrying about chain slack take up for personal bikes.