Rear derailleur replacement

[Nedrow]

My bike's rear derailleur has been damaged beyond repair. It's a Shimano 11 speed RD 6800. I cant find a replacement in stock so would like to know if an RD R8000 would be a like for like replacement please.

[Eyebrox]

No. Different ratios since Ultegra changed from 6800 to 8000. They are hard to source but Bike Inn in Spain has some stocks in its Shimano shop. You'll also find some used versions on eBay but no guarantee they work well or will last. A quick search on Google produced this: (short cage)

https://cyclein.co/components/gears-dri ... -28t__9121

[NickJP]

A 105 5800 derailleur would also be compatible.

[Nedrow]

Thanks for the info., I'm glad I didn't place the order. The cassette is a 32T and the cage measures 120mm so long cage needed. I'll investigate the 105 version.

[TheBomber]

No. Different ratios since Ultegra changed from 6800 to 8000.

Are you sure about that? I thought all road 11 speed was interchangeable. The change in pull ratio happening in the switch from 10 speed to 11 speed.

It's a Shimano 11 speed RD 6800. I cant find a replacement in stock so would like to know if an RD R8000 would be a like for like replacement please

They’re both in the same compatibility box here:
https://productinfo.shimano.com/#/com/? ... acid=C-450

[gxaustin]

I thought all road 11 speed was interchangeable.

I thought this was the case too

[Eyebrox]

Shimano changed the pull ratio in Tiagra (10sp), 105 and Ultegra (11sp) four years ago. You need the old style mechs for old style cassettes and new style mechs for new style cassettes. They almost work - but start to struggle on changes on the biggest three cogs. Problem is there are no new "old-style" Shimano kit out there. Bike shops are full of R7000 and R8000 bits but no 5800s or 6800s. You'll find loads of the new stuff on Gumtree and eBay - being sold by people who bought them in error instead of the old 105 and Ultegra equipment.

[Nedrow]

Thanks again for all advice so far. I was thinking that the shifters would simply move the derailleur to a certain position with each 'click' and that the derailleur played no active part in positioning once aligned etc. I'm now hoping I can now 'resurrect' the original part since buying a replacement seems unlikely.

[TheBomber]

Shimano changed the pull ratio in Tiagra (10sp), 105 and Ultegra (11sp) four years ago.

Are you saying that Shimano changed the pull ratio between 6800 and R8000 - which are both 11 speed groupsets? In which case why does the compatibility chart that I linked previously show them as being interchangeable?

I was thinking that the shifters would simply move the derailleur to a certain position with each 'click'

Each click moves the derailleur a certain number of millimetres to the side. Prior to 11 speed the derailleur used to move about twice as far as the lever had pulled (the 'pull ratio'). To improve accuracy this ratio was changed to about 1:1 with 11 speed. Eyebrox seems to be saying that this changed again since, but that doesn't seem to agree with Shimano's documentation - hence my question above.

[gxaustin]

Are you saying that Shimano changed the pull ratio between 6800 and R8000 - which are both 11 speed groupsets? In which case why does the compatibility chart that I linked previously show them as being interchangeable?

I think I'd go with Shimano's compatibility chart - the manufacturer should know his products.

[gxaustin]

You need the old style mechs for old style cassettes and new style mechs for new style cassettes.

And yet the spacing on all Shimano 11 speed cassettes is the same and they fit on the same freehubs. So that can't be true. How do I know - I have used both with my 6800 groupset.
Surely pull ratio is set by the shifter - after all that's what does the pulling.
My understanding is that the pull ratio was changed after the 6700 series because this (10speed) groupo had the gear cables running under the bar tape and the change wasn't as good as before. Increasing the pull ratio overcame the cable friction better.
The Tiagra 4700 series (10 sp) had the revised pull ratio because it too has gear cables running under the bar tape.

This is what Brucey wrote;
"9000, 6800, 5800 (11s) all use a different shift ratio -in both FD and RD- vs older groupsets and (with the right cables) shift OK. They use about 2.7mm cable pull per rear shift.

DA, Ultegra, 105 10s groupsets in hidden cable form (7900, 6700, 5700) use the 'old' shift ratios (~2.3mm cable pull per rear shift) and this combined with underbartape routing means that these groupsets tend to be very sensitive to cable condition.

Shimano had at least three goes at cable sets for these groupsets which used various forms of coated inner cable. These 'worked' in that they initially offered lower friction, but all too often the coating came off the inner cable and managed to clog the outer cable.

When Tiagra went 10s with 4700 (and GRX 10s arrived later on) they both used the 'new' shift ratios as per the 11s groupsets (about 2.8mm cable pull per rear shift, in 10s form, which happens to be near-identical to 8s cable pull per rear shift too).
When Sora went 9s, they stuck with the 'old' RD shift ratio (so about 2.5mm cable pull per rear shift) but used the new shift ratio for the FD. {edit; in doubles but not triples]

So all current shimano groupsets with hidden cables use at least 2.5mm cable pull per rear shift, and seem to work OK. But uniquely in the case of 9s, the same cable pull per shift is used in older washing line shifters too, which makes them more tolerant of cable condition."

[fredN4]

You need the old style mechs for old style cassettes and new style mechs for new style cassettes.

And yet the spacing on all Shimano 11 speed cassettes is the same and they fit on the same freehubs. So that can't be true. How do I know - I have used both with my 6800 groupset.
Surely pull ratio is set by the shifter - after all that's what does the pulling.
My understanding is that the pull ratio was changed after the 6700 series because this (10speed) groupo had the gear cables running under the bar tape and the change wasn't as good as before. Increasing the pull ratio overcame the cable friction better.
The Tiagra 4700 series (10 sp) had the revised pull ratio because it too has gear cables running under the bar tape.

This is what Brucey wrote;
"9000, 6800, 5800 (11s) all use a different shift ratio -in both FD and RD- vs older groupsets and (with the right cables) shift OK. They use about 2.7mm cable pull per rear shift.

DA, Ultegra, 105 10s groupsets in hidden cable form (7900, 6700, 5700) use the 'old' shift ratios (~2.3mm cable pull per rear shift) and this combined with underbartape routing means that these groupsets tend to be very sensitive to cable condition.

Shimano had at least three goes at cable sets for these groupsets which used various forms of coated inner cable. These 'worked' in that they initially offered lower friction, but all too often the coating came off the inner cable and managed to clog the outer cable.

When Tiagra went 10s with 4700 (and GRX 10s arrived later on) they both used the 'new' shift ratios as per the 11s groupsets (about 2.8mm cable pull per rear shift, in 10s form, which happens to be near-identical to 8s cable pull per rear shift too).
When Sora went 9s, they stuck with the 'old' RD shift ratio (so about 2.5mm cable pull per rear shift) but used the new shift ratio for the FD. {edit; in doubles but not triples]

So all current shimano groupsets with hidden cables use at least 2.5mm cable pull per rear shift, and seem to work OK. But uniquely in the case of 9s, the same cable pull per shift is used in older washing line shifters too, which makes them more tolerant of cable condition."

Interesting, the final paragraph. Recently fitted a 9 speed sora shifter with a deore 9 speed rd. Wasnt easy to index. Whereas an old washing line 9 speed ultegra indexed much easier, until the brake cable hook fell off! Spare part on its way from SJS.

[gxaustin]

Recently fitted a 9 speed sora shifter with a deore 9 speed rd. Wasnt easy to index. Whereas an old washing line 9 speed ultegra indexed much easier, until the brake cable hook fell off! Spare part on its way from SJS.

I've used an XT mech with Ultegra 10s without problem.
AFAIK all Shimano 9s whether mtb or road is compatible; and so is 6600.