We've discussed the differences and pros and cons between center lock and 6 bolt rotors at some length before (a post which is actually one of our most read ever), but why are there rotors at any price between $20 and $90?
As you see in the array of rotors in this photo (pretty freaking arty, too, huh?!?!?), there are both center lock and 6 bolt rotors, and there are one piece and 2 piece rotors. And there are solid rotors and rotors with all sorts of crazy cutouts.
6 bolt rotors can come in one or two piece types. One piece rotors are obviously the easiest and cheapest to make. You cut a flat plate into shape and you're done. A 2 piece rotor has that operation, plus you need to make the carrier core, and then you need to attach the two. So more expensive to make, and therefore more expensive to buy.
2 piece rotors have several benefits. Lighter weight is not among them - they're a bit heavier. The otherwise-the-same Avid one and two pice rotors from this photo have a 30g difference between them (I KNOW - criminal!!). So why would I choose for myself and recommend the two piece? Two piece rotors are stiffer and less likely to warp. The carrier is a stiffer structure than the simple plate and it provides better support to the business end of the rotor. I'm sure at some level there's also a detectable difference in braking power/modulation/things-that-don't-have-established-vocabulary-around-them aspects. Two piece are also better at shedding heat. The aluminum carrier core is a better heat sink than steel plate.
The Ultegra rotor in the photo (the one that looks unlike any of the others) is sort of a special beast. The large fins that you see between the carrier and rotor actually get sandwiched between the rotors two layers of steel. This is designed to be a high speed conduit for heat to get out of the rotor and onto the fins, where it will be dissipated quickly. Really good design, and if you are doing big technical descents, worth having.
Then there are different rotor materials. I'm no metallurgist, but when one rotor says "use with resin pads only" then I am sure that the steel alloy used in that rotor is different, and not as good as the one that allows you to use either resin (aka organic) or metallic (aka sintered) pads. I know I wrote a post about the difference between the two at one point but can't find it. Anyway, metallic pads have more bite, are less likely to suffer brake fade in hard braking, and are generally less prone to noise and last longer, but that comes at some expense to the longevity of your rotor. In these "use with resin pads only" rotors, I guess that their what must be significantly softer metal gets the heck beaten out of it by metallic pads. So despite the lower cost, unless you are just toodling around town on your bike in a way that I think few people are doing with our wheels, the "resin pad only" rotors are a bad look and a false economy.
And that's what I have to say about that.
5 comments
…but Dave,
https://xkcd.com/386/ !!!
Zach – good points generally, but welcome to the limitations of a ~600 word limit (where people check out and stop reading or don’t bother starting in the first place).
And yeah the Shimano cooling is an excellent design.
Trade offs in materials, design, and effective transfer of info exist everywhere. This isn’t stump the chump or the NEJM, it’s a service to efficiently and hopefully entertainingly get quite accurate and usable info to people of very broad knowledge levels. I think we do that every damn time out. Is someone who’s read this post likely to be a way more informed rotor consumer for having read it? 100% yes.
Thank you.
Rob and Brett – Thanks.
I don’t think the whole aluminum core thing is quite as clear cut as you’re thinking it is. First up, on the heat dissipation bit – sure, aluminum is a better heat sink material than steel, but that interface between the steel disc and aluminum carrier is a terrible conductor of heat. On some rotors, the way the two pieces are joined likely does a better job of preventing heat from reaching the carrier than it does of allowing heat to be pulled into the carrier.
Similarly, the AL carrier can certainly be nice & stiff, but due to the much different CTE’s of AL & Stainless, that stiffness is not necessarily an advantage. In fact, if you had a perfectly stiff interface between them and excellent conduction of heat between the Stainless rotor & AL carrier, the rotor would be more likely to warp, not less (AL carrier will grow more with temperature than the stainless rotor & something would have to give). Fortunately all the reasonably good rotor designs out there take this into account in how they attach the rotor to the carrier, and the really good ones result in floating rotors (aka, absolutely not firmly attached to each other). Unfortunately, the more the rotor design leans towards avoiding heat related warping, the worse the interface between the two materials becomes at conducting heat. Along the same lines, this is why the cooling fins on the ice tech & freeza rotors is part of the disc & not the carrier. If those fins were on the carrier, their effectiveness would be greatly diminished.
Great post. Shimano ice tech rotors are far better than anything else I have tried. Long life span and consistent powerful braking.
One other comment is that you should match your rotors to your calipers. All calipers are not created the same! I thought I’d pick up a set of Shimano Icetech rotors for my new Easton tubeless wheels (thanks, November!), but on doing some research, the pads on my Avid BB7s would be too wide for the rotor and would end up sweeping part of the carrier arm as well. Shimano apparently uses a narrower pad.