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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Shimano,Black,ERDM3100SGS Alivio Alivio M3100 Rear derailleur, 9-Speed, Shadow Design, SGS Long cage

Product ID: 241101188

Details

Brand
SHIMANO
Color
Black
Item Weight
0.2 kg
Material
other
Mounting Type
Braze-On Mount

🔧SGS long cage for smooth chain tension

⚙️9-speed precision shifting

🛡️Shadow RD tech for impact protection

334.03 DT

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Description

⚙️ Shift into adventure mode with Shimano Alivio – where precision meets durability!

LIGHTWEIGHT ROBUST - Crafted from steel and aluminum for a perfect balance of strength and weight at just 0.2 kg.
TRAIL READY DURABILITY - Shadow RD design minimizes damage from trail obstacles, keeping your ride smooth and worry-free.
EFFORTLESS INSTALLATION - Designed for quick setup with basic tools, so you can get back on the trail faster.
SEAMLESS 9 SPEED SHIFTING - HyperGlide system ensures crisp, reliable gear changes for every terrain.
OPTIMIZED CHAIN MANAGEMENT - SGS long cage maintains perfect chain tension, reducing wear and boosting drivetrain longevity.

The Shimano Alivio M3100 Rear Derailleur is a 9-speed, Shadow RD-equipped drivetrain component engineered for trail and trekking bikes. Featuring a flat, impact-resistant design and SGS long cage for optimal chain tension, it delivers smooth, reliable shifting with HyperGlide technology. Lightweight yet durable, it’s easy to install and built to withstand rugged outdoor conditions, making it a top choice for serious cyclists seeking performance and longevity.

Specifications

ASIN	B08CGYD213
Best Sellers Rank	#50,940 in Sports & Outdoors ( See Top 100 in Sports & Outdoors ) #16 in Rear Bike Derailleurs
Brand Name	SHIMANO
Case Material Type	Steel & Aluminum
Color	Black
Customer Reviews	4.6 4.6 out of 5 stars (718)
Global Trade Identification Number	04550170621155
Included Components	Bike Parts
Item Dimensions L x W x H	6.69"L x 4.43"W x 3.94"H
Item Highlight	Alivio RD-M3100 9-Speed Long Cage Rear Derailleur with Shadow RD Tech
Item Type Name	Rear derailleur.
Item Weight	0.2 kg
Manufacturer	Shimano
Manufacturer Part Number	ERDM3100SGS
Material Type	other
Model Number	C8C086
Mount Type	Braze-On Mount
Number of Items	1
Number of Teeth	36
UPC	192790621159
Unit Count	1 Count
Warranty Description	2 Year Manufacturer

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334.03 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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