Is this compatible for 8 speed?

Not perfectly - the m3100 model is really meant for 9 speed

Will this replace the stx rc on a Trek 7300 8 speed?

Shimano's Compatibility charts won't show this "9-speed" derailleur as compatible with 8-speed components, but it should work just fine. Shimano 8-speed shifters will work. This RD can handle larger cogs than were common in the 8-speed era, up to 36t largest cog, but assuming you have 11-32 it'll work. I have an stx rc RD on one of my bikes, and wouldn't hesitate to try this as a replacement.

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Black,ERDM3100SGS Alivio Alivio M3100 rear derailleur, 9-speed, Shadow design, SGS long cage

Product ID: 300020054

Details

Brand
SHIMANO
Colour
Black
Item weight
0.2 Kilograms
League
Canadian
Material
Aluminum

⚙️9-speed precision shifting

🛠️SGS long cage for wide-range gears

🚵‍♂️Durable Alivio-grade MTB trail ready

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Description

🚵‍♂️ Shift Like a Pro, Ride Like You Own the Trail!

EXTENDED SGS LONG CAGE - Maximize your gear range with a long cage design that handles wide-range 9-speed cassettes effortlessly in 1x or 2x setups.
TRAIL READY DURABILITY - Built with premium aluminum and steel materials, this derailleur withstands rugged MTB conditions for reliable everyday riding.
SMOOTH 9 SPEED SHIFTING - Experience flawless gear transitions with Shimano’s trusted Alivio technology, engineered for consistent trail performance.
PRECISION CABLE PULL GEOMETRY - Enjoy accurate, positive gear engagement across all sprockets, ensuring you never miss a beat on challenging terrain.
SEAMLESS SHIMANO COMPATIBILITY - Optimized for Alivio M3100 groupsets and compatible 9-speed drivetrains, making upgrades and replacements hassle-free.

The Shimano RD-M3100 Alivio SGS 9-Speed Rear Derailleur combines durable construction with precise cable pull geometry and an extended long cage to deliver smooth, reliable shifting across wide-range 9-speed MTB drivetrains. Designed for trail and recreational mountain biking, it ensures consistent performance and compatibility with Shimano Alivio M3100 groupsets.

Specifications

ASIN	B08CGYD213
Best Sellers Rank	#53,434 in Sporting Goods ( See Top 100 in Sporting Goods ) #34 in Bike Shifters & Parts
Brand Name	SHIMANO
Case Material Type	Steel & Aluminum
Color	Black
Country of Publication	Japan
Customer Reviews	4.6 4.6 out of 5 stars (696)
Global Trade Identification Number	04550170621155
Included Components	SHIMANO,Black,ERDM3100SGS Alivio Alivio M3100
Item Dimensions L x W x H	17L x 11.3W x 10H centimeters
Item Type Name	SHIMANO,Black,ERDM3100SGS Alivio Alivio M3100 rear derailleur, 9-speed, Shadow design, SGS long cage
Item Weight	0.2 Kilograms
League Name	Canadian Football League
Manufacturer	Shimano
Manufacturer Part Number	ERDM3100SGS
Material Type	Aluminum
Model Number	C8C086
Mount Type	Shimano Rear Direct Mount
Number of Items	1
Number of Teeth	36
UPC	192790621159
Unit Count	1 Count
Warranty Description	Shimano Standard Warranty

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399.13 DT

Duties & taxes included

In stock

Sold byAmazon TunisiaDelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

Buyer Protection · Full refund if your order doesn't arrive as described.

Desertcart purchases this item on your behalf and handles shipping, customs, and support to Tunisia.

Secure transaction

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TrustScore 4.5 | 7,300+ reviews

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