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: 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 MTB trail-ready design

€ 79.20

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Description

⚙️ Shift like a pro, ride like a legend.

EXTENDED SGS LONG CAGE - Maximize your gear range with a cage designed to handle wide-range 9-speed cassettes effortlessly.
SEAMLESS COMPATIBILITY - Optimized for Shimano Alivio M3100 groupsets and 9-speed MTB drivetrains for plug-and-play performance.
TRAIL READY DURABILITY - Built with Alivio-grade materials to withstand the rigors of everyday mountain biking adventures.
SMOOTH 9 SPEED SHIFTING - Experience flawless gear transitions tailored for trail and recreational MTB rides.
PRECISION CABLE PULL GEOMETRY - Shimano’s engineered design ensures accurate, positive engagement across all sprockets.

The Shimano RD-M3100 Alivio SGS 9-Speed Rear Derailleur combines precision engineering and durable construction to deliver smooth, reliable shifting for mountain bikers. Featuring an extended SGS long cage for wide-range gear compatibility and Shimano’s signature cable pull geometry, it ensures consistent performance on trails and recreational rides. Designed specifically for 9-speed MTB drivetrains, this derailleur offers dependable, high-quality shifting that keeps you ahead of the pack.

Specifications

ASIN	B08CGYD213
Best Sellers Rank	#15,469 in Sporting Goods ( See Top 100 in Sporting Goods ) #5 in Bike Shifters & Parts
Brand	SHIMANO
Brand Name	SHIMANO
Case Material Type	Steel & Aluminum
Color	Black
Colour	Black
Customer Reviews	4.6 out of 5 stars 672 Reviews
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
Item weight	0.2 Kilograms
League	Canadian Football League
League Name	Canadian Football League
Manufacturer	Shimano
Manufacturer Part Number	ERDM3100SGS
Material	Aluminum
Material Type	Aluminum
Model Number	C8C086
Mount Type	Shimano Rear Direct Mount
Mounting type	Shimano Rear Direct Mount
Number of Teeth	36
UPC	192790621159
Unit Count	1 Count
Warranty Description	Shimano Standard Warranty

Reviews

H**S

Shimano Alivio RD-M3100

En orginal Shimano bakväxel som funkar helt perfekt som utbytesväxel

25.11.2025

L**S

Bien

Muy bueno calidad precio, cambia los comicios muy suave

24.05.2025

A**L

Op tijd bezorgd

Prima

8.09.2025

R**O

Facile installazione

Cambio 9 V con vite di regolazione guaina , ottimo prodotto con spedizione ultraveloce , pacchetto un po’ anonimo ma completo x cui soddisfatto

23.07.2025

W**N

Good buy

Easy to use an install , good quality, way to adjust , and functions well

20.12.2025

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€ 79.20

Duties & taxes included

In stock

Sold byAmazon CroatiaDelivered 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 Croatia.

Secure transaction

Trustpilot

TrustScore 4.5 | 7,300+ reviews

Sneha T.

Received my product in pristine condition. Great service overall.

1 month ago

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

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