avid hsxcl 180mm brake rotor centerlock avid logo

Avid (Sram) HSX Centerlock (that is, HSXCL) rotor, new addition to Merida

I’m no huge fan of disc brakes, and the front disc on Merida is annoying me. It’s a Deore series, SM-RT64, 180mm. Advertised as 164 grams, never bothered weighing it myself.

There are lots of problems about this particular model, but even with my rear, XTR rotor, too. The obvious one is, its too flexy and bent very easily. I true it quite frequently, and it gets bent after applying brakes for the first name, no matter how soft and gentle I treat it. Problem looks to be the rotor material itself; which almost acts like a spring steel, but obviously not. Second problem, no proper aluminium spider: XT’ s and XTR’s does not bend. At least, that much: and yes, even my XTR rotor at back bends, albeit at a negligible amount.

I was looking out for a proper rotor some time, and this Avid rotor was a steal: 10 years ago, Avid HSX models were as expensive as, and sometimes more expensive then Shimano XTR’s. The last price I remember was 60$. I bought this one for just 21$! If I were to buy a RT54 Deore, I’d pay just 1 or 2$ less. And at least 3x for XTR.

Obviously, as you can see from the packaging, this is new-old stock. Avid started making HSX and HSXCL rotors in mid-2013, and this is 2013 model.

I’m not a fan of Shimano rotors for various reasons:

  • Braking surface material is weak, prone to bend very easily, and warps too much under heat.
  •  XTRs, and XTs to some degree are fine because they have large aluminium spiders. These serve 2 purposes: reinforce the flexy braking surface and cool the disc effectively. Problem is, they seem to be priced based on the radius of the spider! Especially, even the new SLX spiders are miniscule. That’s a shame because in every other component, even the Deore line is perfect. But for rotors, XT is the absolute bare minimum – not even SLX!
  •  Shimano rotors are not brake pad friendly. I’ve all sorts of exotic discs and pads on my cars, and even the most aggressive Wilwood rotors I had were much more friendlier to pads. Shimano design not just shaves pads like butter, but also have very few braking surfaces in the wrong place.
  •  The steel they use is probably fit for knive manufacturing better. Under heat and pressure, the braking surface becomes a shiny and slippery surface. This is called “glazing”, but should not be considered as a daily fact, with such “civilised” braking.

Design-wise, Avid, now Sram, HSX looks perfect: hole sizes are ideal, placed just right, and there are no slots to shave pads that already don’t have much life in them. Spider is huge, on XTR level or better. But the real advantage of it is the material: it is exceptionally solid. I really mean it. It is solid as a cast iron car brake rotor. Yeah, I’m exaggerating, but it is SOLID.

The braking surface looks almost identical to SM-RT10’s, which I believe is a Tourney or maybe even lower end. My wife’s bike has those, which fades terribly with even the best genuine Shimano resin pads, unlike rotors, which perform admirably well. While high-end IceTech rotors like XT  and XTR, have aluminium “carrier” sandwiched between 2 solid steel braking surfaces, they are all one piece of ..solid metal. Avid or now Sram, never resorted to such level of “sophistication”, maybe because sophistication not just work sometimes.

A small word on floating rotors

I’ ve seen such kind of rotors with aluminium spiders advertised as “floating rotors” many times. This is based on motorcycle design, and SOMEWHAT works for them – but never seen one working on an MTB: an ordinary motorbike with a floating rotor probably have more then 10x more piston pressure compared to MTB brakes, and (maybe) can deflect braking area a little bit. It’s a floating rotor or not, for MTB’s. In fact, what they call “floating rotor” these days is actually permit MUCH LESS lateral movement then an ordinary rotor made out of stamped steel!

Two different parts riveted together doesn’t make a floating rotor, its a very different thing. It solves a huge problem about not just MTB brakes, but motorcycle brakes, too: pistons on each side of caliper does not press the braking surface at the same time, so in theory, and in practice too, this tends to bend discs, and it does. In cars, we have floating calipers to tackle the issue. Since bikes cannot have such bulky calipers, and braking force is probably too weak it to make it work properly, we have floating discs…or not. Floating discs extends out of spider, or carrier (correct term) because rivets permit some degree of lateral movement. This is also the tell-tale manifestation of the fact that caliper pistons do not effectively position themselves to compensate for brake pad wear. I’m not too familiar with motorcycle brakes, but refurbished quite a lot of car calipers. When you see car calipers and bike calipers together, you’ll get it why they wouldn’t work, at least, how they should. To be perfectly honest though, even the calipers in cars are far from perfect, at least most of them. Most people won’t notice, services don’t care; but crazy amount of cars are running with sticky, rubbing brakes to some degree.

I think the whole thing started with 2-piece rotors on racing cars, which serves a purpose and solves some problems instead of creating new ones. These are called 2-piece rotors for some time, then called floating rotors. They do not float, too. The problem they solve is, weight and heat. They weigh much less, because the carrier is almost always aluminium, and they dissipate heat much better, while single piece, cast iron rotors tend to keep themselves hot very well. That’s why humanity used cast iron as radiators in the past, now replaced by aluminium because its cheaper to make and fits better to individual heating solutions such as gas boilers. Later, I think they realised there is a “potential” amongst performance motorbike owners, because some motorbikes suffered from the same issues, too.

I’ve seen Hope discs advertised as fully floating, but didn’t see how they work in real life..just in pictures. Galfer, which makes racing motorbike rotors (they are pretty serious about that) seem to have a proper floating rotor, but didn’t see one, try one – and probably never will, unless it cost me an arm and a leg.

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