How did you really setup your R8000/9000 Rear Derailleur B-GAP?

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MagicShite
Posts: 55
Joined: Sun Jun 26, 2016 3:33 pm

by MagicShite

According to the si.shimano.com manual, the B Gap is set when you are on the little ring and at your biggest sprocket (30T in my case with short cage). It should be set in such a way that there is little to no rubbing/noise when you backpedal. This method will now make sure the top jockey wheel is as close as possible to the largest sprocket. Take note that this is the exact method I used for 6800 RD and it works excellently.

The problem with R8000 is that if you do the above method, you will now have shifting noise (crunching) when shifting from the previous cog to the largest (downshifting). It seems like something is impeding the shift. Now to solve this you will have to increase the B-Gap. At this point it seems like you're setting it like MTB 11-50 wide range cassettes.

The B-Gap at this point seems to be quite large than usual. What's the actual method for setting B-GAP?

by Weenie


wingguy
Posts: 4321
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

Tbh the key part is the 4th paragraph in the manual end bolt section, after you’ve set it super close, shift into the inner chainring and the 11t and then use the end bolt to eliminate any chain slack. It’ll naturally end up a fair bit further out than the initial position.

MaxPower
Posts: 123
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

wingguy wrote:
Thu Oct 03, 2019 4:47 pm
Tbh the key part is the 4th paragraph in the manual end bolt section, after you’ve set it super close, shift into the inner chainring and the 11t and then use the end bolt to eliminate any chain slack. It’ll naturally end up a fair bit further out than the initial position.
this - i run 11-30, short cage, 34/50 front. If you size the chain according to the manual (big/big + 2 links) the cage will be at its most rear/slack position when in small/small and the B-tension skrue has to be adjusted to take the last slag.

Shifting is a bit noisy with the R8000. I found that correct setup will result that you can JUST change into the 11T and JUST rid in the 30T without it grinding like mad. This is because of cable tension and not affected by both H/L limit screws (as even if the H/L screws are adjusted to not touch the RD in outer positions, the cable tension keeps the RD in this tight range - at least on my bike).
The FD tolerances for rub are also VERY tight in my opinion.

I think i end up with about 4-5mm of gap between upper pulley and the 30T cog - If this shift has i grinding noise, i found that the gap is too small and need another 1mm or 2 to become noisy but with no "grinding" (and i don´t meen grinding noise like bad indexing - its different på grinding, more like the upper pulley hitting the cog type of sound)

MaxPower
Posts: 123
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

BTW - i have seen people set the shadow RD´s up like the old range (b-tension) and it looks terrible - but seems to shift fine enough, so don´t go OCD over it... I try at least not too (after spending like 10 hours of adjusting the hell out of FD/RD and cable tension - I find the r8000 at least to need very precise adjustment to work properly and at its best - but i don´t like electronic shifting, so its just how it is)

MagicShite
Posts: 55
Joined: Sun Jun 26, 2016 3:33 pm

by MagicShite

wingguy wrote: Tbh the key part is the 4th paragraph in the manual end bolt section, after you’ve set it super close, shift into the inner chainring and the 11t and then use the end bolt to eliminate any chain slack. It’ll naturally end up a fair bit further out than the initial position.
Funny enough, this doesn't work. My chain is sized correctly.
MaxPower wrote: this - i run 11-30, short cage, 34/50 front. If you size the chain according to the manual (big/big + 2 links) the cage will be at its most rear/slack position when in small/small and the B-tension skrue has to be adjusted to take the last slag.

Shifting is a bit noisy with the R8000. I found that correct setup will result that you can JUST change into the 11T and JUST rid in the 30T without it grinding like mad. This is because of cable tension and not affected by both H/L limit screws (as even if the H/L screws are adjusted to not touch the RD in outer positions, the cable tension keeps the RD in this tight range - at least on my bike).
The FD tolerances for rub are also VERY tight in my opinion.

I think i end up with about 4-5mm of gap between upper pulley and the 30T cog - If this shift has i grinding noise, i found that the gap is too small and need another 1mm or 2 to become noisy but with no "grinding" (and i don´t meen grinding noise like bad indexing - its different på grinding, more like the upper pulley hitting the cog type of sound)
So considering your gap at 4-5mm, basically on your setup your gap isn't "as near as possible" to the 30T right? My gap is even less than yours at this point but it's impossible to get it set as per shimano instruction. My Chain again is sized correctly.
MaxPower wrote: BTW - i have seen people set the shadow RD´s up like the old range (b-tension) and it looks terrible - but seems to shift fine enough, so don´t go OCD over it... I try at least not too (after spending like 10 hours of adjusting the hell out of FD/RD and cable tension - I find the r8000 at least to need very precise adjustment to work properly and at its best - but i don´t like electronic shifting, so its just how it is)
haha, I see. I wonder if the si.shimano.com manual is actually missing something important. They could be doing the good old "all manuals are written by interns" sorta of thing.

I have my share of experience from the 1x11/1x12 era, so I would tend to set the R8000 a bit differently than the manual considering the grinding noise I get from shifting to the 1st cog (largest) from the 2nd cog (2nd largest)

wingguy
Posts: 4321
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

MagicShite wrote:
Fri Oct 04, 2019 9:17 am
wingguy wrote: Tbh the key part is the 4th paragraph in the manual end bolt section, after you’ve set it super close, shift into the inner chainring and the 11t and then use the end bolt to eliminate any chain slack. It’ll naturally end up a fair bit further out than the initial position.
Funny enough, this doesn't work. My chain is sized correctly.
It honestly does work. How have you sized your chain?

I guess if you had a short range cassette you could size it properly for big-big and still have no initial slack to dial out for small-small, but screw it, just dial a bit out anyway to get the gap that makes it quiet. That’s how it’s supposed to be set up, so no need to overthink it.

MagicShite
Posts: 55
Joined: Sun Jun 26, 2016 3:33 pm

by MagicShite

wingguy wrote: It honestly does work. How have you sized your chain?

I guess if you had a short range cassette you could size it properly for big-big and still have no initial slack to dial out for small-small, but screw it, just dial a bit out anyway to get the gap that makes it quiet. That’s how it’s supposed to be set up, so no need to overthink it.
Sized exactly using Shimano's Guide, BIG-BIG plus a 2 links.

No slack on small small using this config. It's running quite close to the chainstay but there's no slack at all. The pulley is in fact quite far from the 11T when at the smaller chainring.

hlvd
Posts: 325
Joined: Sat Mar 05, 2016 4:54 pm

by hlvd

Have you read this?


Optimal Chainlength - It's A New Day
https://r.tapatalk.com/shareLink/topic? ... source=app


Sent from my iPhone using Tapatalk

wingguy
Posts: 4321
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

MagicShite wrote:
Fri Oct 04, 2019 12:20 pm
Sized exactly using Shimano's Guide, BIG-BIG plus a 2 links.

No slack on small small using this config. It's running quite close to the chainstay but there's no slack at all. The pulley is in fact quite far from the 11T when at the smaller chainring.
Sounds surprisingly tight. What does it look like on big big now?

MagicShite
Posts: 55
Joined: Sun Jun 26, 2016 3:33 pm

by MagicShite

hlvd wrote:
Fri Oct 04, 2019 12:50 pm
Have you read this?


Optimal Chainlength - It's A New Day
https://r.tapatalk.com/shareLink/topic? ... source=app


Sent from my iPhone using Tapatalk
Thanks for the link! It really helped me out on understanding the new derailleurs.

I used a slightly different method now. I added another 2 links as per +3 links method instead of +1, the derailleur angle looks much better.

Now to set the B-Gap I simply shift to small small and set the B-Gap in such a way that i get the chain tensioned properly (as close as possible). This way when I shift up to the largest cog I also have zero noise.

The derailleur don't feel so much different from before, but the angle looks much less extreme when in BIG-BIG now.

by Weenie


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