alexk_il

Watched a few youtube videos explaining how to measure the correct chain link. Got it. Then found online chain length calculators. Makes sense too. But now I totally confused.

So, assuming I know my bike's chain stay...

• Do I measure the length on my bike or do I simply set the number of links exactly as recommended by calculators
• Also, this calculator sometimes comes up with odd number of links. Do I round up or down to make it even?

Thanks

smd4

No need to use a calculator. The chain should not be too tight on big chain ring/big cog (i.e, the rear derailleur should not be stretched so far that there's no room for it to move any further), nor sagging on small chainring, small cog.

Iride01 

I'm not sure why you would not follow the advice from the manufacturer of your rear derailleur. Shimano puts it in their DM's and other documents. https://si.shimano.com/#/

Even for the same DR, Shimano sometimes has different procedures to determine chain length depending on how many chainrings the front has.

However you are essentially wanting the chain to be long enough to go into the big/big combo without pulling the rear DR cage to it's forward limits or to the point of it tangling up with the cassette. AND, you don't want it so long that when in the small/small combo the rear DR cage can't take up the chain slack and is on it's rearward limits of travel.

Though it seems like with some old Shimano DR's with a 3x front they actually told you not to use the lowest gearing. This might be when the mantra and dogma of "Don't cross chain or bad stuff will happen" came into wide spread misunderstanding.

Normally I've found that running the chain over the big/big combo without going through the rear DR and adding a couple links works great for the bikes I've had. And seems to be the most universal way to size a chain.

pdlamb

Um, aren't you missing a "not" between "would" and "follow"?

Other than that, I agree with @smd4. This is one of those things where a few minutes with hands on hardware will give you results that are probably better than what your calculator gives you, and a lot quicker, too!

timdow

If you use an on the bike method, without running chain through rear derailleur, wrap chain around big ring and biggest cog, then add two links. I have not used mullet cassettes though.... I just read online that this method is only good for 36T and under.

If it is not exact, I personally err on the short side for the chain as I would never be in big ring big cog combo, or anywhere close to it. On the other hand, it is a lot easier to remove a link if the chain turns out to be too long than to add a link.

cxwrench

You should rethink giving advice on a mechanical forum. Please. Whether or not you think you'll 'never go big/big' it's stupid to cut a chain too short to do it. For the OP: Forget calculators. They're not the correct way to adjust chain length. Every manufacturer has instructions for how to size a chain for their numerous derailleurs. Find those instructions. Use those instructions. You will never go wrong doing this.

pdlamb

I would never shift into a big-big combo, either. Except that I have on multiple occasions. It's all too easy to lose concentration and shift into the big cog when you were sure you were in a small ring that turned out to be a big ring. Happens to me a couple times a year, when I'm tired, distracted, hot. Because I've sized for big-big, I've managed to avoid damaging anything when I do something stupid like that.

smd4

I just sized my chain using the Shimano instruction for my particular derailleur. Worked great!

alexk_il

Looks like you missed the word "dummies" in the Title of this post. Thank you for the tip though. Will read Shimano's guides too.

alexk_il

From Shimano instructions for MTBs:Seems to be aligned with the calculators and with the internet wisdom.

Thanks

smd4

Happily, I don’t own a mountain bike. The directions for sizing my chain are completely different.

SoSmellyAir

Since it does not seem to have been pointed out yet, the OP should recognize that, whichever proper method is used to size the chain, there is a narrow range of chain lengths -- rather than only a single chain length -- which works for a given drivetrain setup. So I would err on the side of slightly longer, and if there is enough slack in big/big and too much slack in small/small, remove a link.

alexk_il

​​​​​​You mean, remove two links, right?

SoSmellyAir

Yes, I meant a pair; otherwise you can no longer reconnect the chain.

alexk_il

Me neither. Just planning to install mtb gears on my hybrid bike. 🤦🏻😁

But, Shimano instructions are the same for road bikes with more than 28t on the back. No difference with MTB. I think.

mitchmellow62

So many people mistakenly call a half link a "link" that to avoid any confusion Park Tool says to add 2 rivets (or 1 inch) to the length of the chain when using the big-big method. A small point but I think it adds some clarity.

DaveSSS 

The terminology used by chain manufacturers lists 114 links for a 57 inch road bike chain, so a link is only 1/2 inch, but chain length can only be changed in 2-link or 1 inch increments. There is no half link. Chain length calculators work for road bikes, but suspended MTBs may require other procedures to account for suspension movement.

The calculation is not complicated. Add the total of the big/big chain ring and sprocket and divide by 4. Add twice the chain stay length. Add 1 inch extra to go through the RD. Round up unless the total is barely over an even inch value. That's the shortest possible chain. I can use that length, but I add another inch, as long as the chain doesn't hang loose or rub on itself in the little ring and smallest useable sprocket. With sram axs the RD won't shift into the little ring and 10T, only the 11T. I use a 55 inch chain for 415mm stays and 48/36 big/big.

cxwrench

Putting the chain on the bike and sizing it less complicated. Every time. And you don't want the shortest possible chain, you want the longest/safest/most smooth running.

mitchmellow62

I think we're demonstrating the confusion of terminology I was talking about. For some, such as https://www.supercrossbmx.com/blogs/...alf-link-chain and https://www.sheldonbrown.com/deraile...ent.html#chain a full link of a bicycle chain is 1 inch or 2 pins/rivets/rollers. I still like the way Park Tool counts pins/rivets/rollers when they describe sizing chain.

metalheart44

I can't find these instruction on the Shimano website for an Ultegra 8050 rear derailleur .... where did you find them?

smd4

Page 134. Out of a 169 page manual. That electronic crap is way too complicated for me...

Shimano Manual

metalheart44

Thanks, l

squirtdad

I use and like the small small sizing

urbanknight

Technically, one link is a set of inner AND outer plates. You're thinking of two "half links".

What matters most is that you all were talking about the same thing and understanding each other.

cyccommute 

I prefer the Park Tool method which is to use 2 rivets. It’s less ambiguous. Picture stolen from that article