Peter@vecchios said:
Nope. 8/9/10s rear derailleurs(only exception being DA 8s) all have the same dimension and are cross compatible with different 'speed' shifters. a shimano MTB rear derailleur, even tho '9s' will shift 10s spacing fine and dandy w/o any modification or gizmo.
Well, that isn't an accurate statement ...
The 8-/9-/10-speed Shimano rear derailleurs do
not have the same dimensions.
FWIW. The length of the parallelogram of the 8-/9-speed XTR is 45mm (hinge pin to hinge pin). I measure the anchor point for the rear derailleur cable as being 20mm from the rear hinge.
Since my recollection is that the 8-speed 105 rear derailleur
looks like the XTR's parallelogram, I would suppose that the 8-speed ROAD rear derailleurs also have 45mm parallelograms.
The 9-speed XTR rear derailleurs (e.g., 952) that I have are same as the 8-speed XTR rear derailleurs (950 & 951/[rapid rise]) except for the number of teeth on the pulley wheels + a cosmetic difference in the derailleur hanger bolt.
A 9-speed Ultegra 6503 rear derailleur's parallelogram is 43mm long, but the anchor point remains at 20mm from the rear hinge. Despite the difference in the length of the 9-speed ROAD parallelogram, the apparent reason that a Shimano MTB rear derailleur can be substituted for one of the 9-speed ROAD rear derailleurs is because the SLANT (the plane in the Z-axis) is at a steeper angle on the 9-speed rear ROAD derailleurs, thus both the 8- and 9-speed Shimano rear derailleurs apparenty have the same horizontal cage movement.
Now, the 10-speed Ultegra rear derailleur has an even shorter parallelogram (38mm) & steeper SLANT, but the anchor point is decidedly further from the rear hinge (22.5mm) -- approximately the same change in distance that using the
hubbub.com anchoring would achieve when applied to an 8-/9-speed Shimano rear derailleur.
Now, while one might suppose that the combination of changes might account for continued interchangeability, I will note anecdotally that a 'quick' non-road test of a 10-speed Ultegra rear derailleur with its "normal" rear derailleur cable anchoring + 10-speed Campagnolo Ergo shifter yielded the same shifting rate as with either a 9-speed XTR or Ultegra rear derailleur with the hubbub.com anchoring + 10-speed Campagnolo shifter --
that may only be a fortunate coincidence
for me since my preference is to use Shimano rear derailleurs/etc. (I
love Shimano EXCEPT for their shifters) mated to Campagnolo shifters!
The 10-speed Shimano rear derailleurs retain the double-bladed "molly" hook/(washer) that was originally introduced with the "regular" 8-speed Shimano rear derailleurs to allow them to be used with the original, 8-speed DA shifters (i.e., Shimano's ALTERNATE ANCHOR POSITION @ 9 o'clock).
To achieve BACKWARD compatibility when using a 10-speed Shimano rear derailleur with a 9-speed cassette & shifter you would more-than-likely use the ALTERNATE REAR DERAILLEUR CABLE ANCHORING POSITION (I don't remember the documentation indicating this, BTW, and I don't have a sheet handy), hence the legacy molly "washer."
Peter@vecchios said:
a shimano MTB rear derailleur, even tho '9s' will shift 10s spacing fine and dandy w/o any modification or gizmo.
I can neither refute nor confirm this statement through direct application ... but, I would be inclined to believe it is incorrect based on my successful substitution of a 10-speed Shimano rear derailleur for a 9-speed rear derailleur which was hubbub'd -- that suggests to me that a 9-speed Shimano MTB rear derailleur may
NOT be directly interchangeable "w/o
any modification or gizmo" (e.g., shiftmate) when used with a 10-speed Shimano shifter & cassette.
So, while I was grateful that Shimano's 8-/9-speed MTB & ROAD shifters & rear derailluers are indeed interchangeable despite what Shimano's marketing and/or tech people apparently indicated back at the turn of the Century, when my wife told me that the 12-27 cog wasn't giving her a low enough gear -- since I had a 12-32 & XTR rear derailleur -- it was only a question of a few minutes of parts swapping to determine that Shimano's folk were inaccurate with regard to the
mandate to only use components from a given group in a given drivetrain (i.e., only 105 with 105, Ultegra with Ultegra, DA with DA, XTR with XTR, etc.), otherwise who knows if-or-when I would have crossed the threshold of investigating possible component compatibility.
While I think my experience is reproduceable, if someone wants to adhere to whatever-or-whichever "conventional wisdom" they are familiar with with regard to the rear derailleurs & shifters, then that is their prerogative.
But, if anyone ends up with unsatisfactory results when trying to use their 8-/9-speed Shimano rear derailleur with a 10-speed Shimano drivetrain, or vice-versa, then I think it is worth trying the alternate anchoring positions.