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 Alivio RD-M3100 Rear Derailleur - 9-Speed, Long Cage

Product ID: 351880891

Details

Brand
SHIMANO
Colour
Black
Item Weight
200 Grams
Case Material Type
Aluminium
Mounting Type
Clamp-On Mount

🔧45T chain wrap capacity

⚙️9-speed precision shifting

🛡️Shadow RD tech for derailleur protection

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COP 612647

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Description

⚡ Shift like a pro, conquer every trail.

LONG CAGE CAPACITY - Handles up to 45 teeth for versatile gearing on steep climbs and fast descents.
LIGHTWEIGHT COMPACT - At just 0.4 kg and a sleek 15 cm profile, it’s built for speed without bulk.
DIRECT MOUNT STABILITY - Shimano Rear Direct Mount ensures a secure fit and enhanced drivetrain performance.
TRAIL READY DURABILITY - Shadow RD tech keeps your derailleur safe from rocks and roots, so you never miss a beat on rugged trails.
SMOOTH 9 SPEED SHIFTING - Experience crisp, reliable gear changes that keep your ride fluid and efficient.

The Shimano Alivio RD-M3100 Rear Derailleur is a 9-speed, long cage component featuring Shadow RD technology for low-profile protection against trail obstacles. With a 45-tooth chain wrap capacity and Shimano’s direct mount system, it delivers reliable, smooth shifting and durability for serious mountain biking.

Specifications

ASIN	B08CGYD213
Best Sellers Rank	#54,828 in Sports, Fitness & Outdoors ( See Top 100 in Sports, Fitness & Outdoors ) #64 in Bike Derailleurs & Parts
Brand	SHIMANO
Brand Name	SHIMANO
Case Material Type	Aluminium
Colour	Black
Country Of Origin	USA
Customer Reviews	4.6 out of 5 stars 659 Reviews
Global Trade Identification Number	04550170621155
Item Weight	0.2 Kilograms
Manufacturer	Shimano
Manufacturer Part Number	ERDM3100SGS
Material	Aluminium
Material Type	Aluminium
Model Number	C8C086
Mount Type	Clamp-On Mount
Mounting Type	Clamp-On Mount
Number of Teeth	45
UPC	192790621159

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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COP 612647

Duties & taxes included

In stock

Sold byAmazon ColombiaDelivered 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 Colombia.

Secure transaction

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