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: 241101188

Details

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

🔧SGS Long cage for smooth chain management

⚙️9-Speed precision shifting

🛡️Shadow RD tech for impact protection

$84.27

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Description

🚴‍♂️ Shift into adventure mode with Shimano’s stealthy precision!

TRUSTED PERFORMANCE - Backed by Shimano’s 2-year warranty and a 4.6-star rating from over 600 riders worldwide.
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.
OPTIMIZED CHAIN CONTROL - SGS Long cage enhances chain tension and stability, reducing chain drops on rugged rides.
SEAMLESS 9 SPEED SHIFTING - HyperGlide system ensures crisp, reliable gear changes for every terrain.

The Shimano Alivio M3100 Rear Derailleur features advanced Shadow RD technology and a 9-speed HyperGlide system, delivering durable, smooth shifting for trail and trekking cyclists. Its SGS long cage design optimizes chain tension, while the steel and aluminum build ensures lightweight strength. Highly rated and backed by a 2-year warranty, it’s engineered to elevate your ride with reliable performance and protection against trail impacts.

Specifications

ASIN	B08CGYD213
Best Sellers Rank	#35,779 in Sports & Outdoors ( See Top 100 in Sports & Outdoors ) #11 in Rear Bike Derailleurs
Brand	SHIMANO
Brand Name	SHIMANO
Case Material Type	Steel & Aluminum
Color	Black
Customer Reviews	4.6 out of 5 stars 687 Reviews
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 Type Name	Rear derailleur.
Item Weight	0.2 Kilograms
Manufacturer	Shimano
Manufacturer Part Number	ERDM3100SGS
Material	other
Material Type	other
Model Number	C8C086
Mount Type	Braze-On Mount
Mounting Type	Braze-On Mount
Number of Teeth	36
Product Dimensions	6.69"L x 4.43"W x 3.94"H
UPC	192790621159
Unit Count	1.0 Count
Warranty Description	2 Year Manufacturer

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TrustScore 4.5 | 7,300+ reviews

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$84.27

Duties & taxes included

In stock

Sold byAmazon USADelivered 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 USA.

Secure transaction

Trustpilot

TrustScore 4.5 | 7,300+ reviews

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Fast shipping and excellent packaging. The Leatherman tool feels very premium and sturdy.

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The MOLLE sheath is of exceptional quality. Very happy with my purchase.

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