Ultegra R8000 - Chain Length Woes

requiem

Hi All

I decided to build myself a second bike up, as I thought it would be both fun and educational - both of which have very much been the case so far!

I am now approx 95% of the way through the build, and I've hit my first real snag.. I cannot set a chain length which is long enough to allow for big/big, without there being slack in the system when in small/small.

My Kit:
R8000 RD ("GS" / Medium Cage)
R8000 Cassette (11-32 )
R8000 Crankset (52/36 / "Mid Compact")
KMC X11 EL chain (114 links as sold)
Trek Emonda ALR - Size 52 (410mm Chainstay Length)

The reason I selected these particular variants for the build, is because these ratios are precisely what I am running on my Canyon which has a 105 5800 groupset - and runs perfectly. I love the 52 big ring, with the flexibility to go as low as 36/32 on the hills.

Now, I am at a complete loss as to why there seems to be no way to accommodate this chainring/cassette combination with the R8000 group.

I have subsequently noticed that on the Canyon website for example, while all older 6800/5800 Ultimate models were specc'd with 52/36 and 11/32 - the newer R8000 models still ship with Mid Compact rings but with 11-28 cassettes. Similarly, on CRC in the R8000 groupset builder, the second one selects the 52/36 chainset, the 11-32 cassette option is greyed out. Both of these lead me to suspect that for some reason, the mid compact/11-32 combination is no longer compatible. I am yet to find confirmation of this written anywhere. This suspicion is at odds for however, with a youtube video where the chap is successfully running the same RD as me, Mid Compact rings (albeit Cannondale Spiderrings) with the whopping 11-34 cassette - which in theory should have the same setup issues as mine, though magnified!

Am is missing something very simple with the setup process here? The first method of determining chain length I tried was the classic Park Tool big/big (bypassing RD) plus two rivets. It's a no-go since that leaves me with a ton of slack in the small/small. However, when using the small/small measurement method (through RD) that leaves the chain so tight in big big that the RD pulley cage is almost horizontal. B-screw has also been experimented with, but to no avail. Are there other relevant factors which I may be missing?

Potential workarounds..
I have thought about purchasing an 11-28 cassette to try - however I'd like to take this bike abroad to the mountains, and the whole point of my buying the kit I bought was for the wide range of gear ratios on offer.
Another option I've pondered is sizing down to a Compact Crankset - however (please do correct me if I'm wrong here!) when looking at online gear ratio calculators, it seems that this would only exacerbate the problem, since there is a bigger difference in gear inches at the low/low end, than there is at the big/big? My logic on this one may be way off! I do hope so in fact..
but going from 36/11 to 34/11 is 3.27 to 3.09 (difference of -0.18) gear inches
and going from 52/32 to 50/32 is 1.63 to 1.56 (difference of -0.07) gear inches
Therefore I'd imagine that again, this would only worsen the disparity at the extremes of the scale, since at the low end the chain would need to be shorter to a greater degree than the top end?

Any input on this at all would be most appreciated!

Many thanks,

aberdeen_lune

What position are your jockey wheels when on big big? I would shorten the chain so that on big big the jockey wheels are at the 4 o clock position. That way the chain shouldn't be too slack on the little little gears. Well it works on my 6800 set up fine not sure what's changed on the 8000 rear mech.

requiem

Hi, thanks for your reply.

With a chain long enough to allow for a 4 o'clock (aka good/correct) jockey wheel position in big/big, there is a ton of slack when in small /small - hence my confusion

mercia_man

You are always going to get some slack in small/small when using a wide range cassette. It doesn't matter. You don't want to be using that gear (or big/big) unless by accident as the chain is so out of line.

I have always used the following Shimano-recommended method for adjusting chain length and it has always worked for me on Shimano and Campag systems, on triples, doubles and wide range cassettes. Put the chain through your rear mech as normal on smallest cassette cog and big ring. Adjust chain length until top jockey wheel is directly above the bottom jockey wheel, that is a straight line running through both jockey wheels perpendicular to the ground.

part time waster

I have always set up with small ring, smallest sprocket. Put chain on , then allowed 1cm , near enough , space between
The lower part of the chain and the higher jockey wheel as the rear mech wants to tuck itself under the cassette.
The 1cm gap allows the system to run with the odd jolt not able to let the higher jockey wheel come into contact with the lower part of the chain. You can't really get a longer chain set up than this.
If that doesn't work with your big , big combo I reckon it never will. Tinker with the B screw expected.

timothyw

You've written an awful lot - short answer, don't use small - small gears.

It's noisy, the chain droops and you look like a noob.

Set chain length so you can use big big by looping it around them both and trimming so you leave an extra pair of links, don't use small small and don't worry so much.

sungod

^^^

word up

lesfirth

TimothyW wrote:

You've written an awful lot - short answer, don't use small - small gears.

It's noisy, the chain droops and you look like a noob.

Set chain length so you can use big big by looping it around them both and trimming so you leave an extra pair of links, don't use small small and don't worry so much.

That is all the OP needs to know. Well put.

requiem

I would never find myself using this combination however the point is that it is possible to do so on my canyon with 105 5800 setup of same ratios, with no slack in the chain. It thus far, has proven not to be possible with the r8000 kit. Any worries about looking like a noob are not the point for me whatsoever, it's about the system being mechanically solid, and not having to worry about certain gear combinations (whether optimal or otherwise) which may break something

N0bodyOfTheGoat

https://play.google.com/store/apps/deta ... c&hl=en_GB says hi.

My Cube has 41.5cm chain stays, 50T front, 32T cassette... App says 55 links.
My Voodoo has 44.5cm chain stays, 38T front, 30T cassette... App says 54 links.

And don't use big-big or small-small by choice under load, use the latter with rear wheel in mid air to help remove and replace rear wheel for a puncture or using/removing bike from direct drive turbo.

StillGoing

Shimano specifically say use the big/big measurement for chain length. The R8000 RD is designed not to go small/small otherwise when you go big/big, you'll more than likely rip the RD off.

green_mark

Possibly B-screw is not tight enough.
Or the rear mech is not bolted correctly. refer to:
viewtopic.php?t=13084674#p20290149

sh3p

The 8050 di won't allow you to go small small, I presume this is down to the possibility of the problems your having.

requiem

Hi All,

Thanks for your input. Cracked it! I knew there had to be something wrong somewhere, and it was indeed due to the incorrect mounting of the RD.

@green_mark - thanks for posting the link to the other thread. The shimano tech document for the r8000 RD is one I'd looked through more than once before, but I had failed to note one (clearly critical) point. There are two 'stops' on the new style derailleurs, or more specifically on the 'bracket' which the derailleur is mounted on to - which is in turn to be mounted to the dropout. I had the incorrect (i.e. higher) 'stop' resting on the protruding stopper of the hanger, and as such the RD was mounted further forwards than it should have been. Where in fact using the lower stop ensures that the bracket is horizontal, moving the RD further back.

I now have flawless use of all 22 gears - zero slack in small/small, and big/big running perfectly, with jockey wheels at approx 4 o'clock.

@philthy3 - you're quite right that in the aforementioned manual shimano do specifically recommend that method of chain measurement, thank you. I had noted that before, but of course given my incorrect installation of the rear mech that method gave lots of slack in small/small. It has now worked a treat - so thanks again. However I don't believe that the r8000 RD is not designed to go small/small - hence my refusal to accept slack in said combination (again, not that I'd ever find myself in that gear - but having 'no-go' gears which could actually cause damage is for me - simply not acceptable, I'd sooner have bought a narrower range cassette than have the option to use such combinations.)

Thanks to everyone else also, your input is appreciated. The only real snag ended up being entirely down to an oversight on my part (however I would say the documentation on this in particular is somewhat sparse!) My first build is now complete, very excited to ride it in anger

Andymaxy

One simple check, are you using a short cage RD, but for your ratio your supposed to use a long cage.

requiem

To avoid any confusion in case anyone finds this thread to be of relevance to them, as stated in first post, I am using the 'GS' aka 'medium cage' R8000 rear derailleur. There are two sizes, small which has capacity for up to 28t cassette, and medium with capacity for 34t. Thanks

StillGoing

requiem wrote:

@philthy3 - you're quite right that in the aforementioned manual shimano do specifically recommend that method of chain measurement, thank you. I had noted that before, but of course given my incorrect installation of the rear mech that method gave lots of slack in small/small. It has now worked a treat - so thanks again. However I don't believe that the r8000 RD is not designed to go small/small - hence my refusal to accept slack in said combination (again, not that I'd ever find myself in that gear - but having 'no-go' gears which could actually cause damage is for me - simply not acceptable, I'd sooner have bought a narrower range cassette than have the option to use such combinations.)

I've got R8050 on the main bike with the GS RD and it simply won't allow you to go small/small. As said, Shimano have prevented it in the Di2 versions to stop you ripping the rear mech off if the chain length is set to accommodate small/small. I wouldn't want to do it whilst riding anyway, but its a pain when wanting to drop the rear wheel to fix punctures and can't get the chain in the slackest position possible. R8000 would be designed with the same rationale, but you obviously won't have the electrics preventing you from doing it. Be wary though when you go big/big.

Vino'sGhost

Attention muppetts.

1 use either the big big or small small method

if youve got slack cable, check the mech isnt binding at one of the pivots, apply lube to the mech to free if necessary.

Clean your bikes more often

OR

take it to your LBS who will be happy to extract money to accomodate your mechanical illiteracy as often as required.

StillGoing

Vino'sGhost wrote:

Attention muppetts.

1 use either the big big or small small method

if youve got slack cable, check the mech isnt binding at one of the pivots, apply lube to the mech to free if necessary.

Clean your bikes more often

OR

take it to your LBS who will be happy to extract money to accomodate your mechanical illiteracy as often as required.

If you bothered reading instead of just wading in with your insults, Shimano direct you not to use small/small with the r series rear derailleur. :roll: