Cycling UK Forum

Fascinating - thank you!

I shall report back when the lockdown is over and I have some free-time again to make some accurate measurements...

Brucey wrote:take a 'power ratchet' type shifter (which pulls cable in uniform small increments) and then measure the incremental and cumulative RD movement which results.

I will have to see if I can pick-up a cheap-y on eBay. But how do you accurately measure axial movement of the derailleur itself? I have unused Shimano 9spd,10spd and 11spd derailleurs and a Campag 10s to-hand that I could measure.

Brucey wrote:FWIW you shouldn't lump shimano 7s and 8s in the same boat; they don't have the same spacing.

Yup, understood. What I wrote was ambiguous: I have an RD-7700 derailleur on an 8spd Shimano block with Campag 10s ergos.

Brucey wrote: Campag 10s shifting doesn't have uniform cable pulls through the range so it will never be an exact match for a cassette that does,

The whole non-linearity bit is what I'm most curious about... struggling to see why it's more complex than a cos function that accounts for the slant. In the plane of the derailleurs slant it describes an arc about either of the fixed pivots, no? Although these pivots axes change their distance from the hub (as the upper knuckle rotates around the hanger bolt) I can't see why that would affect the rate of axial movement. I may be missing something though...

Brucey wrote:And I don't think there is any such thing as a SRAM 2:1 shifter for 9s either.

Yes, I'm talking cock. I couldn't find the original page(s) that declared an original 1:1-style 9-spd SRAM shifter worked perfectly with 9spd shimano block and 10spd shimano derailleur. But I see several forum posts elsewhere recommending this combination - the aim being to get a 9spd derailleur with clutch. I now see you can create a Frankenstein mech with the still available 9spd XT and punching-out the lower knuckle,clutch and cage from a donor mech which is my kind off hackery...
http://faqload.com/faqs/bicycle-components/drivetrain/derailleurs/9-speed-clutch-rear-derailleur-mash-up

Thanks,

Tom

cheers[/quote]

https://www.bikeradar.com/news/shimano-deore-m6100-12-speed/
...The RD-M4120-SGS and RD-M5120-SGS rear derailleurs are compatible with both 11- and 10-speed cassettes.
The cable pull ratio between 11- and 10-speed Shimano mountain bike groupsets is very similar, meaning that, according to Shimano either of these derailleurs will “work perfectly as an upgrade option for existing shifters on 10- and 11-speed bikes”.

...which is supported by Shimano's website:
https://productinfo.shimano.com/#/com?cid=C-432&acid=C-435

Over the years I've learnt - to my cost* - that measurements of cable-pull and unofficial compatibility charts between various brands and speeds of shifters and deraillers have been more often wrong than not.*

It appears that current wisdom has it that Shimano MTB 10spd and 11spd differ in terms of:
1. Sprocket pitch/thickness (duh),
2. Shifter cable-pull
3. Derailleur actuation ratios.**

It's not like Shimano to bless things that 'nearly' work, so my money is on the 10spd/11spd actuation ratios being identical after all.

Is there a good repeatable way to measure the end-to-end average-actuation ratio of a mech? Or has someone already done this and proven me wrong in advance

Ta,

Tom


* A 100% failure rate in my admittedly limited experience:
Shimano 9spd spacing doesn't work with a 10spd Shimano mech and SRAM 2:1. Not even close.
And nor do Campagnolo 10spd ergos quite work 7/8spd Shimano derailleur/cassette. It's out at one-end or t'other though I've been putting up with it for tens of thousands of miles...
https://www.cyclinguk.org/cyclists-library/components/transmission-gears/derailleur-gears/shimergo#Shimergo
**I appreciate the last two aren't linear...