Ok, you guys must be wondering why there’s even a review on front derailleurs. Front derailleurs are about the least sexy component on a mountain bike Most people probably never change their front derailleurs in the lifespan of their bikes unless its for upgrading to a higher end model. That’s because front derailleurs seldom fail or break, and with the least amount of care can last the life of most bikes it’s affixed upon.
However, mountain bike technologies are evolving faster by the day, and with long travel suspension bikes being more rideable on the ups rather than just the downs. The long travel bikes are also naturally heavier, and people are beginning to discover that there’s not much places where the big chainring comes into play, and it’s actually more of a hindrance as it reduces the ground clearances around the bottom bracket area. Hence there is a paradigm shift in front crankset philosophy as manufacturers begin to discard the triple ring setup for all-mountain and freeride, and increasing the big ring’s size slightly. With this setup there is not much loss in terms of top speed even when pedalling on the road, as a 36×11 gearing is almost the same as a 44×13. In essence you’ll only lose the highest gear when you change over from a 44/32/22 to a 36/22 crankset. With bikes in the 30lb+ range, that’s no disadvantage at all. Another advantage you’ll get is a cleaner look with less overlap of gear ratios.
Now with the introduction of smaller cranksets/ double ring cranksets, the usual triple ring front derailleur looks abit odd, abit similar to a road derailleur on a mountain bike crankset. The Shimano SLX front derailleur also has a more compact cage with a tighter cage radius to match 36t chainrings, designed to reduce chain drop in granny gear situations and improve clearances for today’s complex suspension system.
At first glance, this derailleur looks just like any other mountain bike front derailleur, albeit with a significantly smaller and curvier front cage. The clamp is for 34.9mm seat tubes, but it comes with shim adapters if your seat tube is of a narrower diameter. Despite it being smaller, it’s actually heavier than the XTR front derailleur I replaced it with at 163grams vs 148grams. But such weight is rather insignificant as the SLX is targeted at the all-mountain market as compared to the XTR’s cross-country crowd. Installation and tuning it is straight forward, no different from all Shimano front derailleurs.
I fitted it onto my bike but I did not use the Shimano SLX FC-M665 double ring crankset that it was meant for. Instead, I already have converted a XTR triple crankset into a bashguard/34t/22t chainring setup, so I tested the derailleur on that combination. Installing it onto my bike, I noticed that I had to clamp the front derailleur about 3mm lower than before, as my big chainring has 2 less teeth count. If you are swapping it with the FC-M665 crankset or using it with 36t chain rings, there should be no difference in the mounting position at all.
From the picture you can see how well it conforms to the curvature of the 34t bashguard, and compared to the original XTR front derailleur it looks far neater. The shorter front cage also improved cross-chaining clearances as there was no rubbing at all. All in all, the SLX front derailleur lends a more purposeful all-mountain look to the crankset and bike.
Up-shifting with the SLX front derailleur is crisp, but with slightly more effort required when compared to my old XTR front derailleur. I suspect it is probably attributed to a stronger spring mechanism in the derailleur. Down shifts are fast and accurate, and I did not experience chain drop or chain skip at all. Over the 3weeks of muddy weather we had, the SLX shifted flawlessly.
Whether you are running the new compact all-mountain cranksets or merely converting your old triple chainring setup to a dual ring, you should take a look at the dual-ring versions of the SLX. Not only they complete the look of the compact ring setup, they also improve clearances and reduce chances of chain drop without compromising on shifting speed or precision.
Shimano also produces the SLX dual-ring front derailleur in top-swing versions (FD-M665) and for freeride frames that utilize 83mm bottom brackets, Shimano offers the Saint versions (FD-M815 and FD-M817)