If you are looking for a new rear derailleur for your 9-speed mountain bike, you might be wondering about Shimano Deore RD-M591 and RD-M592 models.
Both are part of the Deore M590 groupset, which is designed for all mountain and cross country riding. They are compatible with Shimano 9-speed MTB shifters and derailleurs, and have a long cage (SGS) version for triple chainrings.
However, there are some key differences that you should know before making your choice.
Similarities: RD-M591 vs. M592
The RD-M591 and the RD-M592 have a lot in common.
They both have a 9-speed compatible design, a wide link structure for increased rigidity and precise shifting, a direct cable routing to reduce cable friction, and a low profile design to avoid damage from rocks.
They also have similar dimensions and weight, with the RD-M591 being slightly heavier at 299 grams versus 292 grams for the RD-M592.
Both rear derailleurs have similar specs, such as a total capacity of 45T, a max front difference of 22T, and a low sprocket max of 36T.
They have similar features, such as a wide link design for increased rigidity and durability, and a top normal return spring for intuitive operation.
Also Read: Shimano RT66 vs. RT86: Compared
Differences: RD-M591 vs. M592
There are some important differences between these two models.
Derailleur Design
The main difference is that the RD-M591 has a conventional spring design, while the RD-M592 has a Shadow technology.
Shadow technology means that the derailleur has a single tension spring that keeps the cage close to the cassette, reducing chain bounce and noise. This also makes the derailleur more stable and less prone to hitting the chainstay.
Shadow technology is especially useful for riding on rough and bumpy trails, where conventional derailleurs might lose chain tension and cause shifting problems.
Mounting Options
The RD-M591 has a normal mount, while the RD-M592 has a direct mount.
A normal mount means that the derailleur is attached to the frame with a hanger bolt, while a direct mount means that the derailleur is attached directly to the frame without a hanger.
A direct mount has some advantages over a normal mount, such as better alignment, easier installation and removal, and less weight.
However, not all frames are compatible with direct mount derailleurs, so you need to check your frame specifications before choosing this option.
Related: Can you Mix Shimano Groupsets?
Shadow and Standard Rear Derailleurs
The RD-M592 is a shadow rear derailleur, while the RD-M591 is a standard rear derailleur.
A shadow rear derailleur has a low profile design that reduces the risk of being hit or damaged by rocks, branches or other obstacles on the trail. It also has a stronger spring tension that reduces chain slap and improves shifting performance.
A standard rear derailleur has a more conventional design that sticks out more from the bike frame, but it may be more durable and easier to adjust.
Pulley Cage
The RD-M592 has an alloy outer plate and a steel inner plate, while the RD-M591 has both plates made of steel. This makes the RD-M592 slightly lighter (235 g vs. 299 g) and more resistant to corrosion, but also more expensive.
Also Read: Why Shimano is Expensive?
Which one should you choose?
It depends on your personal preference and riding style.
If you want a sleeker, quieter and smoother rear derailleur that can handle rough terrain better; you might prefer the rd-m592 shadow model.
If you want a cheaper, simpler and more robust rear derailleur that is easier to maintain and adjust, you might prefer the rd-m591 standard model.
