## Can't quite get chain right...

Discuss light weight issues concerning road bikes & parts.
sfo423
Posts: 574
Joined: Fri Dec 22, 2006 6:12 pm
Location: San Francisco
I set up my bike chain using the SRAM measurement per their spec for eTap (big/big, no der). I am running a 52/36 - 11-28. When riding and in 36 - 11 or up +2 (I know 36 - 11 and up 1 or 2 are not advisable) the chain is super slack and shifting is not so good. I went to resize the chain for sanity sake.

This is the Park method of big/big (no der.) join at front ring add 2.
This is the chain using the small/small (w/der) and just getting rear der to slightly tension.
I did pull out one inner link before taking images. I am sensing my setup is a 'tweener;" meaning I am in between links.

Is it better to be extra long or slightly short? Keep in mind from images the power link and ability to join (i.e. adding a inner link, which puts me back at droopy chain).

Any ideas? I hate to break chain more than needed.

PS; if using the measurement method, the chain is 53 1/2. Using L=2 (16.375)+(52/4+36/4+1); I get 53 as my chain stay is 40.8cm.
Last edited by sfo423 on Mon Jul 08, 2019 11:57 pm, edited 1 time in total.

TobinHatesYou
Posts: 3777
Joined: Mon Jul 24, 2017 12:02 pm
The photos youâ€™ve provided are useless. What would help are photos of your RD while shifted into big-big and small-small.

Your chain including the quick link on one side should be 53in long if your chainstay measurement is correct. Since you reported 53.5, that means you didnâ€™t account for the quick link and your chain is actually 54in long. In other words your chain is 108 links long, but should be 106. You need to remove one inner link and one outer link.

Also your formula values are messed up. 2(16.063)+(52/4)+(28/4)+1=53.126

That is close enough to 53 that I would round down.

sfo423
Posts: 574
Joined: Fri Dec 22, 2006 6:12 pm
Location: San Francisco
On the formula, I erred in putting numbers in post but spreadhsheet was correct; 53).

As far as rear der; here is the cage in big-big (you can see power link. Odd gearing yes but do I want more cage extension?)
Here is the cage in small-small. The cage is barely under tension.
Here is the cage in small-small but with two links out (didn't remove pin just lined up):

kdawg
Posts: 123
Joined: Wed Nov 20, 2013 9:10 pm
Looks about right to me - I wouldnâ€™t want to go any tighter in big big.
I'm left handed, if that matters.

Nefarious86
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Small small and whatever doesn't leave it loose... People make this so much harder than it needs to be...

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TobinHatesYou
Posts: 3777
Joined: Mon Jul 24, 2017 12:02 pm
kdawg wrote: â†‘
Mon Jul 08, 2019 11:07 pm
Looks about right to me - I wouldnâ€™t want to go any tighter in big big.

It does look borderline, but I think it's also "safe" to ditch one inner/outer pair. The math says so, but maybe his chainstays aren't actually 40.8cm...

My question to the OP is whether shifting is lazy beyond 11->12. If it's lazy beyond that, you have other problems like the b-gap is off, micro-adjust/indexing is off or the hanger isn't aligned well enough.

alcatraz
Posts: 2101
Joined: Mon Aug 29, 2016 11:19 am
Small-small sizing has been the easiest method for me.

The only exception is when I'm sizing a chain for an oversized cassette or chainring tooth difference. If I were running an 11-32t cassette and/or 52/34 chainrings on a short cage derailleur, then small-small sizing could be inadequate. Then I test both combinations before cutting.

Should the chain be too slack in small-small, it's easy to take another 2 links out, provided big-big doesn't overstretch the derailleur and that you're using a quicklink.

sfo423
Posts: 574
Joined: Fri Dec 22, 2006 6:12 pm
Location: San Francisco
40.8 was spec from geo chart on chain stay.

I had the derr hanger alligned recently so its straight.

If in big/big; how far forward would the cage extend until you said 'too far?" In my bib/big rear der picture, I have more to extend forward; but not much.

I agree; this should not be so complicated and I have never had an issue on other bikes. But, sometimes getting it right the first time is best (and I'd hate to rip the derr into the wheel and find myself on my face).

kdawg wrote: â†‘
Mon Jul 08, 2019 11:07 pm
Looks about right to me - I wouldnâ€™t want to go any tighter in big big.

It does look borderline, but I think it's also "safe" to ditch one inner/outer pair. The math says so, but maybe his chainstays aren't actually 40.8cm...

[/quote]

silvalis
Posts: 652
Joined: Mon Sep 07, 2015 1:02 am
Location: Aus
Yup small-small method

Is your top pulley a wee bit close to the largest cog on the fully tensioned pic?
Chasse patate

sfo423
Posts: 574
Joined: Fri Dec 22, 2006 6:12 pm
Location: San Francisco
I pulled a link and buttoned it up.

My gap is closer to 6mm than 8mm. I fit a 6mm allen in between and set it.
silvalis wrote: â†‘
Tue Jul 09, 2019 6:39 am
Yup small-small method

Is your top pulley a wee bit close to the largest cog on the fully tensioned pic?

silvalis
Posts: 652
Joined: Mon Sep 07, 2015 1:02 am
Location: Aus
righto. Wasn't sure on the pictures. Was thinking you could get a smidgeon more tension in small-small if you give the b screw/gap a bit more.
Chasse patate

NiFTY
Posts: 1304
Joined: Sat May 26, 2012 11:26 pm
How tight is the rd in big big now. I use big big often with my 53/39 11-28. But i never use 39-11. Or 39-12. Super rarely 39-13 (uphill flattenig sprint only.
If big big is too tight rd +/- rear wheel +/- chainstay explosion. If too loose small small, just noise or sluggish shifting in a combo rarely used. I err on side of caution
Evo 4.9kg SL3 6.64kg Slice RS 8.89kg viewtopic.php?f=10&t=110579" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

sfo423
Posts: 574
Joined: Fri Dec 22, 2006 6:12 pm
Location: San Francisco
good ride this AM: shifts better & quieter drivetrain.

Still not DA mechanical quiet but good enough.

Methodical
Posts: 91
Joined: Sat Mar 03, 2018 11:40 pm
On that first photo you would need to remove one more link. You are not on the correct link.

Big, Big for me works everytime using Park's method. 11-32 cassette and 50/34 crank.
"Never be afraid to try something new. Remember, amateurs built the Ark, professionals built the Titanic"

Trek Emonda SLR (Rage Red) - 6.27kg
'12 Trek Madone (Black) - 6.96kg
Fujee Espree (Maroon) - 11.02kg

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