Shimano SLX M666 disc brake review

Top notch stoppers

Our rating 
4.5 out of 5 star rating 4.5
GBP £124.98 RRP | USD $198.25
Shimano SLX M666 disc brake

Our review

Great control and rock solid reliability at a remarkably affordable price
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Shimano’s SLX M666 brake packs all the best bits of the latest Japanese anchor generation into a remarkably affordable, top performance package.


The new double-barreled reservoir and master cylinder design has a subtle two-tone finish and the short deeply crooked lever gets tool-free reach adjust. There’s no Free Stroke bite point adjust but that’s a rather underwhelming and stiff feature anyway. 

The easy-fit hinged clamp with hidden safety catch is all present and correct, and syringe based bleeding is easy through the top cap. You get the same Ice Technologies finned heat dissipating pad technology of XTR too. 

This stops the mineral oil internals overheating, even when hammered relentlessly, and performance is superbly consistent. We’ve had no reliability issues with any of the new generation Shimano brakes, even in 18-month-old long-term or regularly crashed sets. You can even run them on cooking oil in an emergency.

Separate part selling means you can choose to run standard single piece steel rotors (£24.99), alloy centre spider rotors (£36.99) in conventional six-bolt or easy-to-fit/remove Center Lock splined versions, or trade up to the heat eating steel and alloy Ice Tech rotors (£44.99). Alternatively if you’re upgrading existing brakes you can buy the fully bled brake kit for just £89.99, making high weight the only potential gripe.


This article was originally published in Mountain Biking UK magazine, available on Apple Newsstand and Zinio.

Product Specifications


Name BR-M666 SLX Brakes (12)
Brand Shimano

Description Average power: 111Nm
Weight (g) 485
Brake Rotor Diameters 160mm 180mm 203mm