I just got a new M5100 rear derailleur and when I mounted it on the bike it seems like the cage is not inline. Is this by design or did I got faulty unit?
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3 Answers
That is a normal looking cage for Shimano's 12 speed derailleurs. While the M5100 is marketed as 11 speeds, it's designed exclusively for the Shimano HG 11 to 51 toothed cassette. This is a common spread of gearing for 12 speed systems (M6100, M7100, M8100, M9100). These utilize the Hyperglide + system, which is a set of design and engineering tweaks to the derailleur parallelogram and cage, cassette shift ramps and tooth profile, chain design, and chainring tooth design. The largest 3 cassette cogs of the M5100 cassette is actually a Hyperglide + design as is the shape and slight offset of the M5100 rear derailleur cage. So, despite being an 11 speed derailleur, it utilizes the 12 speed tech so that it can smoothly climb up and down that wide range, 11 speed, 11-51 tooth cassette.
Here are somewhat poor photos of a 12 speed, XT derailleur (RD-M8100). The first two are the same photo, I've just added a reference line to maybe help see the offset. The third pic is the same derailleur but I've pinched the cable stop and pinch bolt together to move the parallelogram out of the way.
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1Good to know. It seems to work ok (some adjustments are still required). I guess I don't need to worry about it then.– jfoltynCommented Jun 2 at 10:44
This is by design. The tension pulley is twisted slightly out of the plane of the guide pulley. This helps the plane of the tension pulley point toward the chainwheel on the crank and accommodate the chain better in every gear.
With the chain on the largest sprocket the cage points downwards, making the plane of tension pulley tilt outwards, towards the chainring .
With the chain on the smallest sprocket the cage points backwards. This makes the plane of the tension pulley tilt inwards but again towards the chainring, just as can be seen on your photo.
Guide (G) pulley: the one closer to the sprocket
Tension (T) pulley: the "lower" pulley
(I wish I could make some nice sketches about this, can someone help?)
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2Excellent explanation. Makes the MoO very clear. (Mode of Operation) Commented Jun 2 at 13:15
According to this(*) thread it seems to be by design. So if it works perfectly I would not worry. You could also visit a store with bikes with said deraileur and see if those also look similarly bent.
